Stimulation of Na/Ca exchange by the beta-adrenergic/protein kinase A pathway in guinea-pig ventricular myocytes at 37 degrees C.
We investigated the effect of beta-adrenergic stimulation on Na/Ca exchange in whole-cell patch-clamped guinea-pig ventricular myocytes at 37 degrees C. With ion channel and Na/K pump currents blocked, the Na/Ca exchange current (I(Na-Ca) was measured selectively as membrane current inhibited by 10 mM nickel (Ni) during a voltage ramp applied between +80 and -120 mV. Isoprenaline (1 microM) caused an increase in both inward and outward current generated by the Na/Ca exchange, which was prevented by the beta-adrenoceptor blocker propranolol. These data suggest that isoprenaline caused a receptor-mediated up-regulation of Na/Ca exchange activity. Mimicking beta-adrenoceptor activation, either by stimulation of adenylate cyclase with forskolin or by internal dialysis of cells with cyclic AMP (3':5'-cyclic adenosine monophosphate), also increased I(Na-Ca). Using fluorescence Ca measurement, an increase of internal cAMP was shown to increase the rate of transmembrane Ca transport via the Na/Ca exchange. A selective inhibitor of protein kinase A prevented stimulation of Na/Ca exchange by isoprenaline. These data suggest that the underlying mechanism of stimulation was phosphorylation of the Na/Ca exchange protein by protein kinase A. Isoprenaline did not stimulate I(Na-Ca) when experiments were carried out at 20 degrees C, in contrast to the findings at 37 degrees C. Modulation of Na/Ca exchange by the beta-adrenergic pathway may have important physiological consequences for intracellular Ca regulation and electrical activity during hormonal stimulation, or during sympathetic nerve stimulation.
Perchenet
L
L
Hoffman-La Roche, Pharma Division, Basel, Switzerland.
Hinde
A K
AK
Patel
K C
KC
Hancox
J C
JC
Levi
A J
AJ
D000262:Adenylyl Cyclases / Q000378:metabolism; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D000242:Cyclic AMP / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004553:Electric Conductivity; D006168:Guinea Pigs; D006352:Heart Ventricles; D007545:Isoproterenol / Q000494:pharmacology; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D009532:Nickel / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000502:physiology; D013696:Temperature; D015854:Up-Regulation
D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D011943:Receptors, Adrenergic, beta; D017923:Sodium-Hydrogen Exchangers; D009532:Nickel; D011433:Propranolol; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D000262:Adenylyl Cyclases; D007545:Isoproterenol; D002118:Calcium