Potassium-induced changes in the electromechanical and ATPase activity of guinea pig heart.

The effects of various concentrations (0, 0.5, 1, 2, 4, and 8 mM) of potassium chloride on the simultaneously recorded action potential and contractility; and Mg++-dependent, Na++-K+-stimulated membrane ATPase of guinea pig's heart were studied. In KCl-free solution, the inhibition of the Na+-K+-ATPase was associated both with a shortening of the duration of action potential and an increase in the contractility. There was a decrease in the overshoot of action potential and an increase in the resting potential. Potassium chloride produced a concentration dependent lengthening of the action potential duration; decrease in the contraction and resting potential; and an increase in the overshoot of action potential and Na+-K+-ATPase activity. The changes in the action potential and contraction were associated with the changes in the Na+-K-ATPase activity. The changes in the ATPase activity preceded the changes in the action potential and contractility. The involvement of ATPase in the genesis of the resting potential; overshoot and duration of action potential; and contraction has been discussed.