Potentiating effect of potassium on skeletal muscle twitch.

CHAPMAN, J. B. Potentiating effect of potassium on skeletal muscle twitch. Am. J. Physiol. 217(3) : 898-902. 1969.-The electrophysiological, myothermic, and mechanical consequences of raising the external potassium ion (K+) concentration from 2.5 to 5 mM have been investigated in toad sartorius muscles and compared with the effects of nitrate ion. These ions (5 mu Kf and 111.1 mM N03) increased the isometric twitch tension by an average of 207$, and both agents prolonged the active state. In parallel with the mechanical effects, the activation heat was increased by averages of 18 y0 and 16 7; under the influence of 5 mu K+ and 111.1 mM N03, respectively. The elevation of the K+ concentration to 5 mM K+ caused an average depolarization of 10 mv and this was associated with a diminished amplitude and rate of rise of the action potential. The likely effects of the K+induced depolarization and nitrate on the intracellular binding of calcium are discussed, and it is suggested that the availability of intracellular calcium for release during the action potential is increased by raising the K+ concentration to 5 mM.