Is Potassium Responsible for Contraction-Induced Hyperemia?: 1174 Board #29 2:00 PM - 3:30 PM

One theory that has been proposed to explain exercise hyperemia is that vasodilation in contracting skeletal muscle is due to rapid accumulation of K⁺ in the interstitium. Previous descriptive studies have shown that the time course of increased [K⁺] in venous blood following muscle contraction correlates well with the observed time course of changes in blood flow. Interestingly, the vascular smooth muscle response to K⁺ is biphasic, with hyperpolarization and dilation at low concentrations and depolarization and constriction at high concentrations. Theoretically, it should be possible to infuse K⁺ at a concentration which would not change the smooth muscle membrane potential nor blood flow. We reasoned that if K⁺ release from muscle plays a substantive role in contraction-induced hyperemia, imposing a contraction during K⁺ infusion would further elevate interstitial [K⁺] which would cause constriction.

PURPOSE

We hypothesized that contraction during K⁺ infusion would further increase the interstitial [K⁺] causing vasoconstriction.

METHODS

In anesthetized dogs (n=5) hindlimb blood flow was monitored with transit time ultrasonic flowprobes placed around the external iliac arteries. A femoral artery catheter was placed for K⁺infusion. Brief tetanic contractions were evoked by stimulation of the sciatic nerve for 1 sec (50Hz, 0.2ms).

RESULTS

As anticipated, intraarterial infusion of low doses of K⁺ produced dilation, high doses produced constriction, and intermediate doses produced no change in blood flow. Under control conditions, a single titanic contraction increased hindlimb blood flow by 113±15 ml/min. However, at an intermediate infusion rate of K⁺ that did not change blood flow from the baseline, a single contraction evoked an increase in hindlimb blood flow of 43±19 ml/min. In none of the experiments was vasoconstriction observed in response to contraction.

CONCLUSIONS

These data do not support the notion that K⁺ is an important contributor to vasodilation evoked by muscle contraction.

Supported by NIH and VA Medical Research.