Active Monovalent Cation Transport in Canine Cardiac Tissues
Previous investigations suggest that functionally different cardiac tissues have different electrochemical and physiological properties[1–3]. The intracellular ionic distribution of the sinoatrial node or other specialized cardiac conducting fibers differs from the ionic concentrations of contractile ventricular muscle[4–7]. Electrophysiological sensitivity to cardiac steroids such as ouabain in canine Purkinje fiber exceeds the sensitivity to ouabain in the ventricle. K-strophanthin decreases conduction velocity in canine Purkinje fibers at a concentration which did not significantly alter the parameter in the ventricular muscle. A greater sensitivity to ouabain in Purkinje fibers that the ventricular fibers was confirmed by other differences such as K fluxes[10–12]. However, recent studies indicate that partially purified Na+,K+ -ATPase prepared from the bovine false-tendon had no greater sensitivity to ouabain than the comparable Na+,K+ -ATPase preparation from the papillary muscle of the same animal. Although there may be no significant difference in ouabain sensitivity of Na+,K+ -ATPase activity in vitro, the exact biochemical basis of such electrophysiological differences between the conducting fibers and the contractile muscle has not yet been documented.
KeywordsATPase Activity Papillary Muscle Cardiac Tissue Monovalent Cation Cardiac Glycoside
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