Key result
Potassium depletion or ouabain shortens action potential duration and increases contraction in human papillary muscle.
The study demonstrates that changes in action potential duration and force of contraction in human papillary muscle induced by potassium and ouabain may be linked to ATPase activity.
Isolated human tissue effects should not change clinical potassium or digitalis use; hypothesis-generating for ATPase-linked repolarization and inotropy.
The effects of extracellular potassium chloride concentrations (0, 2, 4, 4.6, 5, and 8 mM.) on simultaneously recorded transmembrane action potentials and contractions of human papillary muscle were investigated. In a potassium-free solution the early changes observed were a shortening of the action potential duration (APD) at the 25% level of repolariza-tion, and no change or a slight increase in the APD at the 90% level of repolarization. A temporal relation between the shortening of the APD at the 25% and 50% levels of repolarization and an increase in the force of contraction was observed. A direct relation between the increase in extracellular potassium concentration and an increase in the APD as-sociated with a corresponding decrease in the force of contraction was observed. Ouabain (10-9 and 10-8 M.) produced a shortening of the APD and an increase in the contraction similar to KCl-free solution. Ouabain was ineffective in producing its effects on the muscles prein-cubated in KCl-free solution. Exposure of ouabain treated muscles to a KCl-free solution containing ouabain resulted in a small increase in the contraction and a small shortening of the APD of the muscles. The combined effects of ouabain and KCl-free solution were not greater than the effects of a KCl-free solution alone. It is suggested that the changes in APD and force of contraction might be associated with potassium or oua-bain-induced changes in the adenosinetriphosphatase activity of the heart muscle.
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Prasad et al. (1971) studied Patients undergoing corrective open heart surgery. Extracellular potassium chloride and Ouabain vs. Normal Krebs-Ringer solution (4.6 mM KCl) was evaluated on Transmembrane action potential duration and force of contraction. In human papillary muscle, exposure to potassium-free solution or ouabain shortened the action potential duration and increased the force of contraction, whereas increased extracellular potassium lengthened the action potential duration and decreased contraction.
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