Journal Logo

Original Article

Comparison of Contractile Responses in Isolated Mouse Aorta and Pulmonary Artery

Influence of Strain and Sex

Knapp, Jörg MD*‡; Aleth, Susanne PhD*‡; Balzer, Felix PhD*; Gergs, Ulrich PhD; Schmitz, Wilhelm MD*; Neumann, Joachim MD†‡

Author Information
Journal of Cardiovascular Pharmacology: July 2006 - Volume 48 - Issue 1 - p 820-826
doi: 10.1097/01.fjc.0000232062.80084.4f
  • Free

Abstract

In recent years, the mouse has gained tremendous interest for biomedical research because transgenic and gene targeting experiments can be performed with relative ease in mice and because the mouse genome is sequenced. Because of the increasing experimental use of genetically manipulated mice in cardiovascular research (for review see Refs.1,2) it is imperative to expand our knowledge on mouse physiology including the effects of strain and sex, 2 hitherto somewhat neglected aspects.

There are some reports on functional differences between inbred mouse strains in the literature. Platelet function (as measured by the bleeding time after injury) is different between strains of inbred mice.3 Insulin signaling, analyzed by gene expression of insulin receptor and its substrates, is strain dependent.4 Even ventricular cardiomyocyte nuclear number differed greatly between independent, inbred strains of mice.5 The hemodynamic parameters in isolated mouse hearts exhibited strain differences.6 Differences between strains in heart rate and blood pressure were reported.7,8 The transcriptional overexpression of a transgene can be influenced by the genetic background. For instance, DBA/2 mice and C57BL/6 mice exhibited low- and high-level expression, respectively, of a transgene (manganese superoxide dismutase) which was accompanied by a different phenotype.9 Moreover, the genetic background may be important for knock out studies. The severity of the phenotype (early death vs. more normal life span) of a superoxide dismutase was dependent on which strain was used for the gene ablation (129Sv vs. C57BL/6). Strain differences in mice can be regarded as models for polymorphisms or mutation that exist in human populations. These genetic differences between human groups and/or individuals are gaining interest (because of technical progress in automated sequencing reveals more differences that alter gene function) and are expected to change the practice of drug therapy in the years to come.

Sex differences in mice could also be observed. For instance, sex differences in the behavior of mouse lines commonly used in transgenic studies exist.10 Insulin signaling and blood pressure are not only strain dependent as mentioned above, but also sex dependent.8,4 Even in cardiovascular parameters sex differences have been noted. For example, the genetically induced increased expression of the Na+/Ca2+-exchanger resulted in a more marked rise in [Ca2+]i during metabolic inhibition of myocytes from male than from female mice.11

Sex differences are also of clinical relevance. In the last decade, many reports have noted the influence of sex on cardiovascular disease in humans. These include hypertension, coronary heart disease, atrial fibrillation, and cardiomyocyte apoptosis.12-15

However, data are currently lacking whether strain differences or sex differences are relevant for the study of arterial smooth muscle function in mice.

Initially, we hypothesized that no difference due to strain and sex would exist in isolated vascular preparations. Therefore, we investigated the contractile response in isolated arterial vessels (aorta and pulmonary artery) of mice from different strains (CD1, BL6, and DBA) often used in the generation of transgenic mice. We studied both aorta (as typical conductance vessel) and pulmonary artery (as a model of resistance vessel). We tested several pathways of vasoconstriction16 because they might be differently affected by sex and strain. Therefore, the contractile response in isolated vessels due to depolarization by KCl, α1-adrenoceptor stimulation by phenylephrine (PE) and protein phosphatase inhibition by cantharidin (Cant),17 was investigated. The main conclusions of our work are that strain and sex do have an influence on the contractile behavior in isolated vessels from mice.

METHODS

Vessel Preparation

CD1, C57BL/6 (BL6), and DBA/2 (DBA) mice were purchased from Harlan Winkelmann (Borchen, Germany). Six to 7-month old mice were killed by CO2 gas inhalation. Thoracic aortae and pulmonary arteries were dissected and rinsed in cold phosphate-buffered salt solution (mM: NaCl 137, KCl 13.4, Na2HPO4 8.1, KH2PO4, pH 7.45, 4°C), and loose fat and connective tissue were removed under a light microscope. Size and morphology of the vessel preparations were not different between mouse strains and sex.

Force Measurement-Aorta

Aortic rings, about 2 mm in length, were individually mounted in a dual wire myograph (Model A 410, Danish Myo Technogy A/S, Aarhus, Danmark). Two wires were pulled through the lumen of the aortic segments and mounted according to Mulvany and Halpern.18 Aortic rings were equilibrated in oxygenated physiologic salt solution (PSS) containing (mM) NaCl 118, NaHCO3 25, CaCl2 2.5, KCl 4.7, KH2PO4 1.2, MgSO4 1.2, glucose 5.5, ethylene diamine tetraacetate 0.026 for about 30 minutes at 37°C and subsequently stretched to their optimal lumen diameter for active tension development. This basal tension was determined on the basis of internal circumference-wall tension ratio of the rings by setting their internal circumference to 90% to 100% of what the circumference of the vessels would have been if they were exposed to a passive tension equivalent to a transmural pressure of 100 mm Hg,18 that is, 30 to 35 mN.19,20

Force Measurement-Pulmonary Artery

The experiments were performed with vessels approximately 1.3 mm long when measured between the heart and its first branching point. The passive tension was set to 4 to 7 mN, which is equivalent to a transmural pressure of 25 mm Hg (right ventricular systolic pressure was reported to be ∼15 mm Hg21 or rather ∼31 mm Hg22; transmural pressure 30 mm Hg).23

Experimental Protocol

Vessels were washed with PSS and contracted 3 times by exposure to a high potassium solution (K-PSS) composed of (mM): NaHCO3 25, CaCl2 2.5, KCl 122.7, KH2PO4 1.2, MgSO4 1.2, glucose 5.5 mM, ethylene diamine tetraacetate 0.026 mM. Thus, K-PSS was the same as PSS except that KCl was substituted by NaCl. After washout (PSS) rings were first exposed to increasing concentrations of PE (1 nM to 100 μM; 10 min for each concentration). Subsequently, for relaxation carbachol (1 μM) was added. After washout (PSS) rings were exposed to Cant (dissolved in dimethyl sulfoxide and diluted in PSS; 10 μM for 60min and 100 μM for further 120 min) and changes in force of contraction were recorded for at least 180 minutes. Force was calculated as active wall tension (=increase in vessel wall force about basal tension divided by twice the vessel segment length), that is, mN/mm.18

Chemicals

Cant, PE, and carbachol were obtained from Sigma (Taufkirchen, Germany). All other chemicals used were of analytical or best grade commercially available.

Statistics

Results are expressed as mean ± standard error of the mean (SEM). Students t test (comparison between sexes of a given strain) or analysis of variance (for multiple comparison) with Bonferroni post-hoc test was used for the statistical analysis of the data. A P value smaller than 0.05 was deemed to be statistically significant. In addition logistic regression analysis and χ2 tests used where indicated.

RESULTS

Effects of KCl, PE, and Cant on Force of Contraction in Intact Vessel Rings of Aorta

We investigated the effects of KCl, PE, and Cant on force of contraction in aorta from male and female DBA, CD1, and BL6 mice. Isolated rings were contracted 3 times by high potassium solution (123 mM KCl: K-PSS). After reaching resting tension again, isolated rings were exposed to increasing concentrations of PE (1 nM to 100 μM). Rings were subsequently relaxed until the basal tension was reached again. Then, rings were challenged with 10 μM Cant for 60 minute and 100 μM Cant for additional 120 minutes. A typical recording is given in Figure 1.

FIGURE 1
FIGURE 1:
Representative original recordings of contraction experiments with aortic preparations. A, Original recording demonstrating the effect of KCl (123 mM) and PE (1 nM to 100 μM) on force of contraction in an isolated arterial vessel ring of mouse aorta (DBA male). B, Original recording demonstrating the effect of Cant (10 μM and 100 μM) on force of contraction in an isolated arterial vessel ring of mouse aorta (DBA male). Scales for time in minutes (min) and force of contraction in mN are given.

The effect of increasing concentrations of PE in aortic rings from male and female mice are depicted in Figure 2 (A, DBA mice; B, CD1 mice; C, BL6 mice). Data of maximum effects of all experiments with aortae from male and female mice of each strain are summarized in Table 1.

Table 1
Table 1:
Force of contraction of aortic preparations from different mouse strains.
FIGURE 2
FIGURE 2:
Effects of PE on force of contraction in intact aortic preparations. Isolated intact aortic rings from DBA (A), CD1 (B), and BL6 (C) mice were challenged by KCl (123 mM). After washout and reaching basal tension (PD) again, rings were incubated with increasing concentrations of the α1-adrenoceptor agonist PE (1 nM to 100 μM). Data are presented as means ± SEM of n mice (n = 6 for DBA male and female and CD1 male; n = 12 for CD1 female; n = 4 for BL6 male; n = 11 for BL6 female). Abscissa: concentration of PE (−log M). Ordinate: force of contraction expressed as active wall tension (mN per mm wall length, ie, mN/mm). *Indicates the first significant (P < 0.05) difference versus PD. †P < 0.05 male versus female.

Effects of KCl

In aorta segments from CD1 mice, force induced by KCl was significantly higher in CD1 male compared with BL6 male, DBA male, and DBA female mice. In addition, force was greater in CD1 female and BL6 female compared with DBA male. Thus, great differences in the contractile response due to KCl between different strains exist. For instance, maximum force due to treatment with KCl was about 3 times higher in aortic preparations from CD1 male mice compared with DBA male mice (Table 1). In direct statistical comparison, sex-specific difference in the contractile response due to depolarization by KCl could be observed in CD1 and DBA mice (Table 1).

Effects of PE

The maximum effect of PE was greater in CD1 male compared with CD1 female, BL6 male, BL6 female and DBA female mice. In direct statistical comparison there was a sex difference in CD1 and DBA but not in BL6 mice. Thus, we observed sex and strain-specific differences after α1-adrenoceptor stimulation (Table 1 and Fig. 2).

Effects of Cant

After 60 minutes of exposure to 10 μM Cant, force of contraction was significantly higher in CD1 male compared with DBA male. In addition, force was higher in CD1 female compared with DBA female. Thus, strain-specific differences exists (Table 1). The maximum effect of Cant (100 μM) was significantly greater in CD1 male mice compared with DBA male mice. In addition, force was greater in BL6 female mice compared with DBA female mice. Moreover, in direct comparison more force was generated in CD1 males compared with CD1 females. No difference in sex was observed in BL6 and DBA mice. Thus, we observed strain and sex-specific differences (Table 1).

Effects of KCl, PE, and Cant on Force of Contraction in Intact Vessel Rings of Pulmonary Artery

For comparison, we investigated the effects of KCl, PE, and Cant on force of contraction in pulmonary arteries from male and female DBA, CD1, and BL6 mice. Isolated rings were contracted by high potassium solution (123 mM KCl: K-PSS). After washout and reaching resting tension again isolated rings were exposed to increasing concentrations of PE (PE; 1 nM to 100 μM). Rings were subsequently relaxed until basal tension was reached again. Then, rings were challenged with 10 μM Cant for 60 minutes and 100 μM Cant for additional 120 minutes. The effects of KCl, PE, and Cant in pulmonary arteries from male and female mice of each strain are summarized in Table 2.

Table 2
Table 2:
Force of contraction of pulmonary artery preparations from different mouse strains.

Effects of KCl

In pulmonary arteries from CD1 mice, force induced by KCl was significantly higher in CD1 male compared with CD1 female, BL6 male, BL6 female, DBA male, and DBA female mice. In direct statistical comparison, no differences could be found between sexes in BL6 and DBA mice. As in aorta, great differences in the contractile response due to KCl between different strains exist. In addition, a sex-specific difference in the contractile response due to depolarization by KCl could be observed between CD1 male and CD1 female (Table 2).

Effects of PE and Cant

No differences between strains (of same sex) and sex (same strain) could be observed even in direct statistical comparison in preparations of isolated pulmonary arteries (Table 2 and Fig. 3).

FIGURE 3
FIGURE 3:
Effects of PE on force of contraction in intact preparations of pulmonary arteries. Isolated intact rings of pulmonary arteries from DBA (A), CD1 (B), and BL6 (C) mice were challenged by KCl (123 mM). After washout and reaching basal tension (PD) again, rings were incubated with increasing concentrations of PE (1 nM to 100 μM). Data are presented as means ± SEM of n mice (n = 6 for CD1 male and DBA male; n = 4 for CD1 female, BL6 male, and DBA female; n = 5 for BL6 female). Abscissa: concentration of PE (−log M). Ordinate: force of contraction expressed as active wall tension (mN per mm wall length, ie, mN/mm). *Indicates the first significant (P < 0.05) difference versus PD.

Half-maximal Stimulation by PE

We compared the concentration of PE necessary to induce half-maximal contraction (EC50) of aorta and pulmonary artery. In direct comparison, aortic EC50-values were lower for BL6 and DBA female mice than for their male counterparts. In vessel segments of aorta and pulmonary artery from DBA male mice significant differences could be observed as compared with CD1 male mice (Fig. 4). Hence differences between sexes and between strains exist (Fig. 4).

FIGURE 4
FIGURE 4:
Half maximal concentration (EC50) of PE for aortic and pulmonary artery preparations. EC50 values for PE determined in aortae (A) and pulmonary arteries (B) from different mouse strains as indicated. Data are means of EC50 (nM) ± SEM of n mice (aorta: n = 6 for CD1 and DBA male, n = 12 for CD1 female, n = 4 for BL6 male, n = 11 for BL6 female, n = 5 for DBA female; pulmonary artery: n = 6 for CD1 and DBA male, n = 4 for CD1 and DBA female and BL6 male, n = 5 for BL6 female). *P < 0.05 versus female, + P < 0.05 versus CD1 male.

Phasic Contractions

Stimulation of tonic smooth muscle with, for example, α1-adrenoceptor-agonists is often accompanied by phasic contractions making analysis of measurements difficult. Thus, we compared the occurrence of phasic contractions between all groups tested (Table 3). For BL6 male mice, 10 of 11 aorta segments tested showed phasic contractions after stimulation by PE. In contrast, none of the 6 aortae from DBA male mice tested exhibited phasic contractions. Representative original recordings for BL6 male and DBA male mice are depicted in Figure 5. In pulmonary arteries, neither in DBA male nor in BL6 male, phasic contractions occurred. Data on phasic contractions observed during stimulation by 10 μM PE are summarized in Table 3 and were statistically evaluated. Aortae from BL6 and CD1 mice were more likely to exhibit phasic contractions than from DBA mice (according to logistic regression analysis). The same holds true for pulmonary arteries. χ2 values between P = 0.05 and 0.1 were found when sex differences between the incidences in phasic contraction of DBA (aorta), CD1 (pulmonary artery), and BL6 (pulmonary artery) were compared. P values larger than 0.1 were found in comparison between all the other groups studied.

Table 3
Table 3:
Occurrence of phasic contractions observed in aortic and pulmonary artery preparations from different mouse strains.
FIGURE 5
FIGURE 5:
Occurrence of phasic contractions in aorta segments. Representative original recordings are shown, demonstrating the occurrence of phasic contractions during PE application (1 nM to 100 μM) in isolated aorta segments from BL6 male mice (lower panel). In aortic preparations from DBA male mice (upper panel) no phasic contractions were observed. Scales for time in minutes (min) and force of contraction in mN are given.

DISCUSSION

Molecular genetics has an increasing impact on cardiovascular research. The relatively easy manipulation of the mouse genome make the mouse a very attractive model to analyze genetic modifications and their phenotype, for instance, in cardiovascular research. However, the role of sex and strain differences has not yet been thoroughly considered when generating mice which overexpress a gene of interest in arterial smooth muscle or when gene ablation studies are reported.

Human Sex Differences

Sex differences are also clinically relevant, because these differences exist also in the cardiovascular system of humans. To better understand their causes, there will be an increased search for appropriate transgenic mouse model. Examples for sex differences in humans include: the peripheral blood pressure is higher in men than in premenopausal women. This may be due, in part, to the high estrogen levels in premenopausal women (for review see Ref.12). Indeed, estrogen can relax isolated arteries from rabbits and can attenuate KCl dependent vasoconstriction. The mechanism of the relaxation may involve an estrogen-mediated inhibition of currents through L-type Ca2+-channels in smooth muscle cells by estrogen.24 Moreover, not only the mean blood pressure but also plasma norepinephrine and epinephrine levels are higher in men than in women.25 This might indicate that α-adrenoceptor-meditated vasoconstriction in the arteries is higher in men than women. An additional involvement of the vagus in sex differences of the circulatory function is likely. For instance, vagal stimulation in the heart rate is larger in women and indices of ventricular ectopy are less in women compared with men.12 Hence, a number of hypotheses are conceivable which need to be rigorously tested, not only in human subjects but also in more closely controlled transgenic mouse models.

Mouse Sex Difference

Some examples of sex differences in the cardiovascular system of mice have hitherto been reported. For instance, electrical differences between female and male transgenic mice like inducibility of VT was observed.26 Also the remodeling of the ventricles shows sex differences. Male mice but not female mice developed cardiac dilatation in a mouse model of familial hypertrophic cardiomyopathy, that overexpressed a missense mutation of the α myosin heavy chain gene in the heart.27 Here we found sex-specific differences in aorta of CD1 and DBA mice and pulmonary artery of CD1 mice. CD1 male mice always generated more force compared with all other mice preparations studied. The possible histologic and/or biochemical reasons for these findings need to be addressed. Acute effects like different local levels of vasodilatation by estrogens cannot be an explanation, as the vessels were well washed by exchanges of the buffer, before constriction studies were begun. Chronic effects of sexual hormones or estrous cycle dependent protein expression are more likely to be involved. Otherwise, no sex differences were detected in BL6 mice. Therefore, estrogen effects may either be strain dependent or other additional mechanisms are involved.

Mouse Strain Differences

Differences in smooth muscle function have been noted before, such as interstrain differences in the bronchial responsiveness among inbred mouse strains.28 Some inbred mouse strains were more susceptible to airways constriction to methacholine but the myosin content in the trachealis was not different.28 Considerable differences in physiologic cardiovascular parameters, between mouse strains exist. Differences in ECG between mouse strains were noted early on.29 Finally, in intact mice mean heart rate and heart rate variability exhibited strain differences.30 Mouse strain differences in blood pressure (invasively measured) during anesthesia were described. This was explained by interstrain differences in sensitivity toward anesthetic agents and to opioid agents, not intrinsic properties of the vessels.31

The present study was undertaken to compare the contractile response in various mouse strains often used for the generation of transgenic mice or often cross bred into knock mouse strains. For vasoconstriction we used KCl, PE, and Cant which are representative of different, but important, contractile mechanisms, that is, depolarization, α1-adrenoceptor stimulation and protein phosphatase inhibition.17,32

In aorta, force induced by KCl, PE, and Cant was not different within the groups except for DBA male. Strain differences, in the histology of the adventitia (more smooth muscle cell layers in mouse strains that contract more severely) probably do not account for these differences based on work by others.23 Differences in proteins mediating contraction (actin, myosin, kinases, and phosphatases) are a more plausible explanation for the observed differences but were beyond the scope of the present study, which was intentionally functional.

In addition, phasic contractions of aorta due to stimulation with PE were present in all strains and both sexes studied with the notable exception of aorta from DBA male. This phenomenon was accompanied by the finding that only in aortic segments from DBA male mice the EC50 for PE was higher than in the other vessels studied. Thus, DBA male mice seem to be the most useful to study α1-adrenoceptor stimulation of aortic vessels because phasic contraction will not interfere with the interpretation of the data. The mechanism of tonic versus phasic contraction in smooth muscle preparations and isolated cells (intestine preparations, isolated veins and arteries, isolated smooth muscle cells) are still not completely understood. However, intracellular free Ca2+ levels are involved.16 The phasic component of contraction has been attributed to an inositol trisphosphate-mediated release of Ca2+ from the sarcoplasmic reticulum; the tonic component is explained by Ca2+ entry via the sarcolemma or by inhibition of phosphatase activity.17,33 The elevation of cytosolic Ca2+ leads to activation of myosin light chain kinase and phosphorylation of the myosin light chains which finally triggers the interaction of myosin and actin leading to smooth muscle contraction.16 Myosin is dephosphorylated by a phosphatase, which inhibition (for instance, by phosphorylation of a regulatory subunit) can also lead to contraction.34 In addition, differences in the coupling of smooth muscle cells by connexins may contribute to spontaneous and agonist-induced oscillatory activity. This was demonstrated in a rat model with increased gap junction expression in vascular smooth muscle cells.35 It has also been reported that the probability of triggered cytosolic Ca2+ oscillations increased with the coupling of smooth muscle cells.36 Which pathway actually leads to increased phasic contractions in isolated aortae in strain and sex-specific way still needs to be elucidated.

In summary, our data demonstrate strain and sex-dependent differences in the contractile response of aorta and pulmonary artery of various mouse strains. Thus, when generating new transgenic mouse models in smooth muscle research, the genetic background of mice should be considered.

ACKNOWLEDGMENTS

The skillful technical assistance of Barbara Prystaj and Maria Schulik is gratefully acknowledged.

REFERENCES

1. Doevendans PA, Daemen MJ, de Muinck ED, et al. Cardiovascular phenotyping in mice. Cardiovasc Res. 1998;39:34-49.
2. Hoit BD. Murine physiology: measuring the phenotype. J Mol Cell Cardiol. 2004;37:377-387.
3. Zumbach A, Marbet GA, Tsakiris DA. Influence of the genetic background on platelet function, microparticle and thrombin generation in the common laboratory mouse. Platelets. 2001;12:496-502.
4. Goren HJ, Kulkarni RN, Kahn CR. Glucose homeostasis and tissue transcript content of insulin signaling intermediates in four inbred strains of mice: C57BL/6, C57BLKS/6, DBA/2, and 129×1. Endocrinology. 2004;145:3307-3323.
5. Soonpaa MH, Field LJ. Assessment of cardiomyocyte DNA synthesis during hypertrophy in adult mice. Am J Physiol. 1994;266:H1439-H1445.
6. Grupp IL, Subramaniam A, Hewett TE, et al. Comparison of normal, hypodynamic, and hyperdynamic mouse hearts using isolated work-performing heart preparations. Am J Physiol. 1993;265:H1401-H1410.
7. Desai KH, Sato R, Schauble E, et al. Cardiovascular indexes in the mouse at rest and with exercise: new tools to study models of cardiac disease. Am J Physiol. 1997;272:H1053-H1061.
8. Deschepper CF, Olson JL, Otis M, et al. Characterization of blood pressure and morphological traits in cardiovascular-related organs in 13 different inbred mouse strains. J Appl Physiol. 2004;97:369-376.
9. Raineri I, Carlson EJ, Gacayan R, et al. Strain-dependent high-level expression of a transgene for manganese superoxide dismutase is associated with growth retardation and decreased fertility. Free Radic Biol Med. 2001;31:1018-1030.
10. Voikar V, Koks S, Vasar E, et al. Strain and gender differences in the behavior of mouse lines commonly used in transgenic studies. Physiol Behav. 2001;72:271-281.
11. Sugishita K, Su Z, Li F, et al. Gender influences [Ca(2+)](i) during metabolic inhibition in myocytes overexpressing the Na(+)-Ca(2+) exchanger. Circulation. 2001;104:2101-2106.
12. Reckelhoff JF. Gender differences in the regulation of blood pressure. Hypertension. 2001;37:1199-1208.
13. Price JF, Fowkes FG. Risk factors and the sex differential in coronary artery disease. Epidemiology. 1997;8:584-591.
14. Wolbrette D, Patel H. Arrhythmias and women. Curr Opin Cardiol. 1999;14:36-43.
15. Mallat Z, Fornes P, Costagliola R, et al. Age and gender effects on cardiomyocyte apoptosis in the normal human heart. J Gerontol A Biol Sci Med Sci. 2001;56:M719-M723.
16. Horowitz A, Menice CB, Laporte R, et al. Mechanisms of smooth muscle contraction. Physiol Rev. 1996;76:967-1003.
17. Knapp J, Bokník P, Deng MC, et al. On the contractile function of protein phosphatases in isolated human coronary arteries. Naunyn-Schmiedeberg's Arch Pharmacol. 1999;360:464-472.
18. Mulvany MJ, Halpern W. Contractile properties of small arterial resistance vessels in spontaneously hypertensive and normotensive rats. Circ Res. 1977;41:19-26.
19. Lalli J, Harrer JM, Luo W, et al. Targeted ablation of the phospholamban gene is associated with a marked decrease in sensitivity in aortic smooth muscle. Circ Res. 1997;80:506-513.
20. Liu LH, Paul RJ, Sutliff RL, et al. Defective endothelium-dependent relaxation of vascular smooth muscle and endothelial cell Ca2+ signaling in mice lacking sarco(endo)plasmic reticulum Ca2+-ATPase isoform 3. J Biol Chem. 1997;272:30538-30545.
21. Champion HC, Villnave DJ, Tower A, et al. A novel right-heart catheterization technique for in vivo measurement of vascular responses in lungs of intact mice. Am J Physiol Heart Circ Physiol. 2000;278:H8-H15.
22. Geraci MW, Gao B, Shepherd DC, et al. Pulmonary prostacyclin synthase overexpression in transgenic mice protects against development of hypoxic pulmonary hypertension. J Clin Invest. 1999;103:1509-1515.
23. Chruscinski A, Brede ME, Meinel L, et al. Differential distribution of beta-adrenergic receptor subtypes in blood vessels of knockout mice lacking beta(1)- or beta(2)-adrenergic receptors. Mol Pharmacol. 2001;60:955-962.
24. Kitazawa T, Hamada E, Kitazawa K, et al. Non-genomic mechanism of 17 beta-oestradiol-induced inhibition of contraction in mammalian vascular smooth muscle. J Physiol. 1997;499:497-511.
25. Evans JM, Ziegler MG, Patwardhan AR, et al. Gender differences in autonomic cardiovascular regulation: spectral, hormonal, and hemodynamic indexes. J Appl Physiol. 2001;91:2611-2618.
26. Gehrmann J, Berul CI. Cardiac electrophysiology in genetically engineered mice. J Cardiovasc Electrophysiol. 2000;11:354-368.
27. Olsson MC, Palmer BM, Leinwand LA, et al. Gender and aging in a transgenic mouse model of hypertrophic cardiomyopathy. Am J Physiol Heart Circ Physiol. 2001;280:H1136-H1144.
28. Duguet A, Biyah K, Minshall E, et al. Bronchial responsiveness among inbred mouse strains. Role of airway smooth-muscle shortening velocity. Am J Respir Crit Care Med. 2000;161:839-848.
29. Goldbarg AN, Hellerstein HK, Bruell JH, et al. Electrocardiogram of the normal mouse, Mus musculus: general considerations and genetic aspects. Cardiovasc Res. 1968;2:93-99.
30. Shusterman V, Usiene I, Harrigal C, et al. Strain-specific patterns of autonomic nervous system activity and heart failure susceptibility in mice. Am J Physiol Heart Circ Physiol. 2002;282:H2076-H2083.
31. Zuurbier CJ, Emons VM, Ince C. Hemodynamics of anesthetized ventilated mouse models: aspects of anesthetics, fluid support, and strain. Am J Physiol Heart Circ Physiol. 2002;282:H2099-H2105.
32. Knapp J, Boknik P, Linck B, et al. Cantharidin enhances norepinephrine-induced vasoconstriction in an endothelium-dependent fashion. J Pharmacol Exp Ther. 2000;294:620-626.
33. Mita M, Yanagihara H, Hishinuma S, et al. Membrane depolarization-induced contraction of rat caudal arterial smooth muscle involves Rho-associated kinase. Biochem J. 2002;364:431-440.
34. Hartshorne DJ, Ito M, Erdodi F. Myosin light chain phosphatase: subunit composition, interactions and regulation. J Muscle Res Cell Motil. 1998;19:325-341.
35. Slovut DP, Mehta SH, Dorrance AM, et al. Increased vascular sensitivity and connexin43 expression after sympathetic denervation. Cardiovasc Res. 2004;62:388-396.
36. Fanchaouy M, Serir K, Meister JJ, et al. Intercellular communication: role of gap junctions in establishing the pattern of ATP-elicited Ca2+ oscillations and Ca2+-dependent currents in freshly isolated aortic smooth muscle cells. Cell Calcium. 2005;37:25-34.
Keywords:

force; phasic contraction; smooth muscle; phenylephrine; cantharidin

© 2006 Lippincott Williams & Wilkins, Inc.