Background and objective:: To compare the inotropic and lusitropic effect of lidocaine and mepivacaine on rat papillary muscle.
Methods:: Effects of lidocaine and mepivacaine (10−8−10−3 M) were studied in rat left ventricular papillary muscles in vitro at a calcium concentration of 1 mmol, under low (isotony) and high (isometric) loads.
Results:: Lidocaine induced a significant negative inotropic effect in isotonic and isometric conditions whereas mepivacaine did not. Mepivacaine only induced a negative inotropic effect when added as a bolus for the highest concentration and this effect was significantly more pronounced with lidocaine than with mepivacaine (active force at 10−3 M: 63 ± 10 vs. 84 ± 10% of baseline, P < 0.05). Increasing calcium concentration resulted in a greater positive inotropic effect in the control (199 ± 11% of baseline) and mepivacaine groups (197 ± 22% of baseline) when compared to the lidocaine group (163 ± 19% of baseline, P < 0.05 vs. lidocaine and control groups), suggesting an impairment on intracellular Ca2+ handling by lidocaine. A negative lusitropic effect under low load was observed only for mepivacaine and suggested an impairment of sarcoplasmic reticulum function. Lidocaine and mepivacaine did not modify postrest potentiation but significantly depressed the force–frequency relationship.
Conclusions:: The negative inotropic and lusitropic effects induced by lidocaine were more important than that of mepivacaine and may involve an impairment of intracellular Ca2+ handling.