Transmembrane potential, contraction and ATPase activity of human heart in relation to ouabain.

Effects of ouabain (10-12M to 10-5M) on the simultaneously recorded transmembrane action potential and contraction; and (Na+K+)-activated membrane ATPase of human papillary muscles were investigated. Ouabain in the concentration of 10-12M did not affect the transmembrane potential, contraction and (Na+-K+)-ATPase activity. Ouabain in the concentrations of 10-11 to 10-7M produced a concentration dependent inhibition of (Na+-K+)-APTase associated with shortening of action potential duration and increase in contraction. Ouabain (10-7M) produced a time dependent inhibition of the (Na+K+)-ATPase associated with the shortening of action potential duration and increase in contraction. Ouabain in the concentration of 10-5M produced an initial marked increase in contraction which was shortly followed by a decrease in contraction and an increase in tone. The muscles developed contracture within 15 to 20min. This concentration of ouabain inhibited the (Na+-K+)-ATPase completely. These results suggest that there is a relation between the inhibition of the (Na+-K+)ATPase and shortening of action potential duration associated with an increase in contraction. Human papillary muscles seem to be very sensitive to the effect of ouabain.