Potassium induced relaxation of vascular smooth muscle: A possible mechanism of exercise hyperaemia

Summary

The relaxing effect of small increases in extracellular K⁺-concentration ([K⁺]₀) on helical strip preparations of the rat aorta, activated by 2 μg norepinephrine/l, was investigated by simultaneously recording mechanical and extracellular mass electrical activity, the latter from two different points. The results of 148 separate experiments show that increases in [K⁺]₀ in a range between 2.7 and 12.7 mM produce decreases in tension corresponding to vasodilation in vivo. The relaxing effect of increasing [K⁺]₀ is temporary, lasting from 30–200 sec, after which propagation of excitation is improved. The temporary relaxation was not present in any of the 66 experiments in which [K⁺]₀ was increased to more than 13 mM; rather, an immediate increase in tension always occurred. The K⁺-relaxation is shown to be a result of a temporary impairment or block of conduction. Hyperpolarization as a result of increasing conductance quotient g_K∶g_Na is discussed as a possible factor in these changes.