Control of Cardiac Sarcolemmal Adenylate Cyclase and Sodium, Potassium-Activated Adenosinetriphosphatase Activities

• Published in: Circulation research 1975-01, Vol.36 (1), p.8-17
• Main Authors: Tada, Michihiko, Kirchberger, Madeleine A, Iorio, Jo-Anna M, Katz, Arnold M
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphatases - metabolism; Adenylyl Cyclases - metabolism; Animals; Calcium - pharmacology; Epinephrine - pharmacology; Guinea Pigs; Myocardium - enzymology; Potassium; Sarcolemma - drug effects; Sarcolemma - enzymology; Sodium
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.RES.36.1.8

A plasma membrane preparation purified from guinea pig ventricles without the use of high concentrations of detergents or structure-disrupting salts was used to compare the mechanisms controlling sodium, potassium-activated adenosinetriphosphatase (Na, K-ATPase) and adenylate cyclase activities. The basal ATPase activity of 4–6 μmoles Pi/hour mg protein, measured in 120 mM NaCl or KC1, was approximately doubled in 100 mM NaCl plus 20 mM KC1. This increment, the Na, K-ATPase, was abolished by 10M ouabain, the KI for ouabain being approximately 3 × 10M. l-Epinephrine had no effect on Na, K-ATPase, but NaF was inhibitory. Adenylate cyclase, which had a basal activity of approximately 200 pmoles cyclic AMP/min mg protein, was increased approximately 50% by NaCl or KC1 alone at concentrations up to 0.2M. There was no additional stimulation of adenylate cyclase activity when Na and K were included together. Both l-epinephrine and NaF caused significant stimulation of adenylate cyclase, but neither basal nor activated cyclic AMP production was influenced by ouabain. Half-maximal stimulation was seen at approximately 5 × 10-M l-epinephrine. Both the catecholamine and NaF increased the Vmax of cardiac plasma membrane adenylate cyclase without significantly influencing3 Km. Increasing Ca2 in the range between 10 and 10M inhibited basal, l-epinephrine-stimulated, and NaF-stimulated activities. Basal rates of cyclic AMP production were more sensitive to Ca than was l-epinephrine-stimulated adenylate cyclase activity, so that Z-epinephrine stimulation was increased from approximately 60% in 0.5 mM EGTA to approximately 150% in 10M Ca and 400% in 10M Ca. The inhibitory effect of Ca on adenylate cyclase activity may represent2+ a negative feedback mechanism by which elevation of intracellular Ca concentration lowers cellular levels of cyclic AMP and thus reduces Ca influx into the myocardium.