On the mechanism of beta-adrenergic regulation of the Ca channel in the guinea-pig heart.
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.(ABSTRACT TRUNCATED AT 250 WORDS)
M
M
Kameyama
F
F
Hofmann
W
W
Trautwein
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007545:Isoproterenol / Q000494:pharmacology; D009206:Myocardium / Q000378:metabolism*; D011494:Protein Kinases / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000502:physiology*
D007473:Ion Channels; D011943:Receptors, Adrenergic, beta; D000242:Cyclic AMP; D011494:Protein Kinases; D007545:Isoproterenol; D002118:Calcium