title: Amiloride: relationship between cardiac effects and inhibition of Na+/Ca2+ exchange.
abstract: The potassium sparing diuretic amiloride at concentrations ranging between 0.1-0.8 mM inhibited the Na+/Ca2+ exchange in sarcolemmal vesicles isolated from beef heart. The rate of exchange activity was 50% reduced by 0.35 mM amiloride. In spontaneously beating atria isolated from normal and reserpinized guinea-pigs, amiloride produced a concentration-dependent positive inotropic effect and negative chronotropic effect (EC50 = 0.7 mM). Amiloride protected spontaneously beating atria and left atria driven at 1 Hz from digitalis cardiotoxicity assessed in terms of a raised end-diastolic tension. It is suggested that the positive inotropic effect, negative chronotropic effect of amiloride and heart protection against digitalis toxicity are related to the observed inhibition of sarcolemmal Na+/Ca2+ exchange activity.
mesh_terms: D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D004070:Digitalis; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism; D010042:Ouabain / Q000633:toxicity; D010946:Plants, Medicinal; D010947:Plants, Toxic; D011719:Pyrazines / Q000494:pharmacology*; D012508:Sarcolemma / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*
chemical_list: D011719:Pyrazines; D010042:Ouabain; D000584:Amiloride; D012964:Sodium; D002118:Calcium