Abstract
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. Thebeta-2 adrenergic agonist zinterol increasedICa 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 μM) of isoprenaline, a nonselective beta adrenergic agonist. Moreover, 3-isobutyl-1-methylxanthine (100 μM), a nonselective phosphodiesterase inhibitor, or forskolin (10 μM), a direct activator of adenylyl cyclase, had no additive effects in the presence of 0.1 μM zinterol. Zinterol had a long lasting action on frogICa because after washout of the drug,ICa returned to basal level with a time constant of 17 min. An application of acetylcholine (1 μM) during this recovery phase promptly reduced ICaback 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 μM, respectively. In all three preparations, intracellular perfusion with 20 μM PKI(15–22), a highly selective peptide inhibitor of cAMP-dependent protein kinase, completely antagonized the stimulatory effect of zinterol onICa. We conclude that beta-2 adrenergic receptor activation produces a strong increase inICa in frog, rat and human cardiac myocytes which is due to stimulation of adenylyl cyclase and activation of cAMP-dependent phosphorylation.
Footnotes
-
Send reprint requests to: Dr. Rodolphe Fischmeister, INSERM U-446, Faculté de Pharmacie, F-92296 Châtenay-Malabry Cedex, France.
-
↵1 This work was supported by a grant from the Fondation pour la Recherche Médicale. V. Arvydas Skeberdis was supported by a fellowship from INSERM (Poste Vert).
-
↵2 Current address: Kaunas Medical Academy, Institute of Cardiology, Laboratory of Membrane Biophysics, Kaunas 3007, Lithuania.
- Abbreviations:
- ACh
- acetylcholine
- CGP 20712A
- 1-[2-((3-carbamoyl-4-hydroxy)phenoxy)ethylamino]-3-[4-(1-methyl-4-trifluoro-methyl-2-imidazolyl)phenoxy]-2-propranol
- IBMX
- 3-isobutyl-1-methyxanthine
- ICa
- L-type calcium current
- ICI 118551
- erythro(±)-1-[(7-methylindane-4-yl)-oxy]-3-isopropylamino-2-butanol
- cAMP
- cyclic adenosine 3′,5′-monophosphate
- Received March 25, 1997.
- Accepted July 22, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|