Changes in sarcolemmal adenosine triphosphatase activity and in ouabain sensitivity of rat myocardium in isoproterenol-induced cardiac hypertrophy.
Sodium, potassium-activated adenosine triphosphatase (ATPase) activity and the sensitivity of rat myocardium to ouabain was studied in isoproterenol (IPR)-induced cardiac hypertrophy. IPR in a dose of 5 mg/kg was administered to rats intraperitoneally, once daily, for seven days. Left ventricular trabeculae originating from IPR-treated rats were significantly less sensitive than controls to ouabain-induced positive inotropy. In crude homogenate and sarcolemmal fractions the ATP hydrolysing activity both in the presence of Mg++ (basic) and Mg++, Na+, K+ (total) was significantly reduced in the heart of IPR-treated rats. The difference between the total and basic ATPase, i.e. the Na+, K(+)-stimulated portion of the activity was slightly reduced, but the sensitivity of Na+, K(+)-ATPase to ouabain remained unchanged. The results indicate that the well-known relation of sodium pump inhibition to positive inotropy in the heart of IPR-treated rats may not be valid.
Szabó
J
J
Department of Pharmacology, Medical University of Debrecen, Hungary.
Nosztray
K
K
Szegi
J
J
D000818:Animals; D006332:Cardiomegaly / Q000139:chemically induced / Q000201:enzymology* / Q000503:physiopathology; D004558:Electric Stimulation; D006321:Heart / Q000187:drug effects; D007545:Isoproterenol; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000201:enzymology* / Q000648:ultrastructure; D010042:Ouabain / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012508:Sarcolemma / Q000201:enzymology*; D012794:Sialic Acids / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D012794:Sialic Acids; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D007545:Isoproterenol