Beta-2 adrenergic activation of L-type Ca++ current in cardiac myocytes.
The whole-cell patch-clamp and intracellular perfusion techniques were used for studying the effects of a beta-2 adrenergic receptor activation on the L-type Ca current (ICa) in frog ventricular myocytes. The beta-2 adrenergic agonist zinterol increased ICa in a concentration-dependent manner with an EC50 (i.e., the concentration of zinterol at which the response was 50% of the maximum) of 2.2 nM. The effect of zinterol was essentially independent of the membrane potential. The stimulatory effect of zinterol was competitively antagonized by ICI 118,551, a beta-2 adrenergic antagonist. The maximal stimulatory effect of zinterol was comparable in amplitude to the effect of a saturating concentration (1 or 10 microM) of isoprenaline, a nonselective beta adrenergic agonist. Moreover, 3-isobutyl-1-methylxanthine (100 microM), a nonselective phosphodiesterase inhibitor, or forskolin (10 microM), a direct activator of adenylyl cyclase, had no additive effects in the presence of 0.1 microM zinterol. Zinterol had a long lasting action on frog ICa because after washout of the drug, ICa returned to basal level with a time constant of 17 min. An application of acetylcholine (1 microM) during this recovery phase promptly reduced ICa back to its basal level suggesting a persistent activation of adenylyl cyclase due to a slow dissociation rate constant of zinterol from its receptor. Zinterol also increased ICa in rat ventricular and human atrial myocytes, and the maximal effect was obtained at 10 and 1 microM, respectively. In all three preparations, intracellular perfusion with 20 microM PKI(15-22), a highly selective peptide inhibitor of cAMP-dependent protein kinase, completely antagonized the stimulatory effect of zinterol on ICa. We conclude that beta-2 adrenergic receptor activation produces a strong increase in ICa in frog, rat and human cardiac myocytes which is due to stimulation of adenylyl cyclase and activation of cAMP-dependent phosphorylation.
Skeberdis
V A
VA
Laboratoire de Cardiologie Cellulaire et Moléculaire, INSERM U-446, Université de Paris-Sud, Faculté de Pharmacie, F-92296 Châtenay-Malabry, France.
Jurevicius
J
J
Fischmeister
a R
aR
D000262:Adenylyl Cyclases / Q000502:physiology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000328:Adult; D000368:Aged; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects*; D020746:Calcium Channels, L-Type; D000242:Cyclic AMP / Q000502:physiology; D004983:Ethanolamines / Q000494:pharmacology*; D005260:Female; D006801:Humans; D008297:Male; D009206:Myocardium / Q000378:metabolism; D010766:Phosphorylation; D011893:Rana esculenta; D051381:Rats; D017208:Rats, Wistar; D018343:Receptors, Adrenergic, beta-2 / Q000502:physiology*
D000318:Adrenergic beta-Agonists; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D004983:Ethanolamines; D018343:Receptors, Adrenergic, beta-2; C002904:zinterol; D000242:Cyclic AMP; D000262:Adenylyl Cyclases