Strophanthidin and force regulation by intracellular sodium activity in cardiac Purkinje fibers.
The role of intracellular sodium activity (aiNa) in the inotropy of a low concentration of strophanthidin (5 X 10(-8 M) was studied in sheep cardiac Purkinje fibers by recording contractile force, aiNa and transmembrane potentials under conditions that vary aiNa. High [Na]O, strophanthidin and tetrodotoxin (TTX) changed force and aiNa in a closely related manner: on logarithmic coordinates, the data were well fitted by a single line obtained through the regression equation F = b (aiNa)s where b represents the intercept and s the slope of the relation. With low strophanthidin, force increases as a linear function of (aiNa) approximately 5 and with high [Na]O as a linear function of (aiNa) approximately 6. However, the combined administration of high [Na]O and strophanthidin results in a potentiated inotropic effect as force becomes a linear function of (aiNa) approximately 14. This potentiation and its abolition by TTX suggests that factors other than aiNa powerfully modify the inotropy of a low strophanthidin concentration.
Abete
P
P
Department of Physiology, State University of New York, Brooklyn 11203.
Vassalle
M
M
D000818:Animals; D004558:Electric Stimulation; D005260:Female; D006329:Heart Conduction System / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects*; D011690:Purkinje Fibers / Q000502:physiology*; D012756:Sheep; D012964:Sodium / Q000502:physiology*; D013327:Strophanthidin / Q000494:pharmacology*
D013327:Strophanthidin; D012964:Sodium