Alterations in the heart sarcolemmal Ca2+ transport activity by some beta-adrenergic antagonists

The effects of some beta-adrenergic antagonists such as acebutolol, propranolol, pindolol and oxprenolol (1-1000 microM) were studied on the rat heart sarcolemmal Ca2+ transport activities. Pindolol enhanced sarcolemmal ATP-dependent Ca2+ binding and Ca2+-stimulated ATPase whereas acebutolol had no effect. Both propranolol and oxprenolol had biphasic actions on the sarcolemmal Ca2+ pump activities; the lower concentrations (1 and 10 microM) were stimulatory, but the higher concentrations (100 and 1000 microM) were inhibitory. None of the drugs used in this study had any effect on Mg2+ ATPase and non-specific Ca2+ binding activities of heart sarcolemma except that 1000 microM propranolol decreased Mg2+ ATPase activity significantly. Mitochondrial and microsomal ATP-dependent Ca2+ binding activities were unaffected by these drugs (1-1000 microM), except that 1000 microM propranolol was inhibitory. These results suggest differences among various beta-adrenergic blocking drugs with respect to their actions on sarcolemmal Ca2+ pump in the myocardium.