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

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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.

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