On the mechanism of beta-adrenergic regulation of the Ca channel in the guinea-pig heart

• Published in: Pflügers Archiv Vol. 405; no. 3; p. 285
• Main Authors: Kameyama, M, Hofmann, F, Trautwein, W
• Format: Journal Article
• Language: English
• Published: Germany 01.10.1985
• Subjects: Animals; Calcium - metabolism; Cyclic AMP - pharmacology; Dose-Response Relationship, Drug; Guinea Pigs; Ion Channels - drug effects; Ion Channels - physiology; Isoproterenol - pharmacology; Myocardium - metabolism; Protein Kinases - pharmacology; Receptors, Adrenergic, beta - physiology
• ISSN: 0031-6768
• DOI: 10.1007/BF00582573

Dose-response relations for the increase in the amplitude of Ca current (ICa) on external application of isoprenaline (ISP) and internally applied cyclic AMP (cAMP) or catalytic subunit of cAMP-dependent protein kinase (C subunit) were established in single ventricular cells of the guinea pig. An intracellular dialysis technique was used. The threshold concentration was for ISP 10(-9) M, for cAMP 3 microM (pipette concentration to which 10(-5) M 3-isobutyl-1-methylxanthine was added) and for C subunit around 0.4 microM (pipette concentration). The concentrations for the half-maximal effect were 3.7 X 10(-8) M (ISP), 5.0 microM (cAMP) and 0.95 microM (C subunit) and for the maximum effect 10(-6) M (ISP), 15-20 microM (cAMP) and 3-4 microM (C subunit). For all three agents the maximum increase in the Ca current density was similar (a factor of 3-4), suggesting that they converge on the same site of the Ca channel. Accordingly, the effects of cAMP and C subunit on ICa were non-additive to those of ISP. From these data the relationship both between concentrations of ISP and cAMP and between those of cAMP and active C subunit in terms of their effects on ICa could be estimated and were compared with those obtained in broken cell preparations. A competitive inhibitor of phosphorylation, 5'-adenylyl-imidodiphosphate (5 mM), greatly reduced the effects of ISP and C subunit on ICa. Cell dialysis with 3 mM adenosine-5'-(gamma-thio)-triphosphate, which produces a dephosphorylation-resistant phosphorylation, markedly potentiated the effects of ISP and cAMP on ICa.