Role of Potassium Ions in the Vascular Response to a Brief Tetanus

Abstract

Changes in the plasma potassium ion (K⁺) concentration in the venous effluent of isolated dog tibialis cranialis and extensor digitorum longus muscles were measured following 1 second of tetanic exercise (32 impulses/sec) during constant-flow perfusion. After a brief delay, venous plasma K⁺ concentration increased to a peak change of 0.23 ± 0.02 mEq/liter and then returned to the control level within 1.5 minutes after the beginning of stimulation, representing a net K⁺ loss of 1.7 µEq/100 g muscle. These experiments indicate a very short period of actual tissue-blood K⁺ transfer, since the time course of the venous efflux can be explained almost entirely by the distribution of vascular transit times. Our best estimate is that a 1-second tetanus produces an immediate 1.3-2.4-mEq/liter increase in interstitial K⁺ concentration which then returns to its control level with a time constant of 6-8 seconds due to rapid cellular reuptake. These K⁺ concentration changes have sufficient magnitude and the correct time course to play a significant role in the production of the vascular response to a brief tetanus.