Abstract
Publisher Summary This chapter presents the contractile force effects of low concentrations of ouabain in isolated guinea pig, rabbit, cat, and rat atria and ventricles. It is well established that active transport of Na,K-adenosine tri phosphate (ATP)ase across cell membranes is catalyzed by Na,K-ATPase and that the binding of ouabain to isolated Na,K-ATPase and the subsequent inhibition of enzyme activity are directly related. The relationship among these events and a positive inotropic action on heart muscle is still the subject of considerable and increasing controversy. The possibility that two or more sites for digitalis binding exist in cardiac sarcolemma either associated, or not, with the Na,K-ATPase, has also been promulgated for years. Stimulation of Na,K-ATPase, transient decrease in intracellular sodium, stimulation of 42K+ uptake and more negative reversal potentials have been reported with very low concentrations of glycosides. The studies presented in this chapter is found that low concentrations of ouabain have no effect on contractile force of papillary muscles of guinea pig, rabbit, and cat. Higher concentrations of ouabain produce in these ventricular preparations the expected increase in contractile force, with subsequent development of toxicity at concentrations of l0–6 M and higher. In strips prepared from left atria, low doses of ouabain produced apparent negative inotropic effects that were shown to be an extension of a continuous natural decline of contractile force.
Published Version
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