Pharmacological characterization of the receptors involved in the beta-adrenoceptor-mediated stimulation of the L-type Ca2+ current in frog ventricular myocytes.
1. The whole-cell patch-clamp was used for studying the effects of various beta1- and beta2-adrenoceptor agonists and antagonists on the L-type Ca current (Ica) in frog ventricular myocytes. 2. Dose-response curves for the effects of isoprenaline (non selective beta-agonist), salbutamol (beta2-agonist), dobutamine (beta1-agonist) on ICa were obtained in the absence and presence of various concentrations of ICI 118551 (beta2-antagonist), metoprolol (beta1-antagonist) and xamoterol (partial beta1-agonist) to derive EC50 (i.e. the concentration of beta-agonist at which the response was 50% of the maximum) and Emax (the maximal response) values by use of a Michaelis equation. Schild regression analysis was performed to examine whether the antagonists were competitive and to determine the equilibrium dissociation constant (K(B)) for the antagonist-receptor complex. 3. Isoprenaline increased ICa with an EC50 of 20.0 nM and an Emax of 597%. ICI 118551 and metoprolol competitively antagonized the effect of isoprenaline with a K(B) of 3.80 nM and 207 nM, respectively. 4. Salbutamol increased ICa with an EC50 of 290 nM and an Emax of 512%. ICI 118551 and metoprolol competitively antagonized the effect of salbutamol with a K(B) of 1.77 nM and 456 nM, respectively. 5. Dobutamine increased ICa with an EC50 of 2.40 microM and an Emax of 265%. ICI 118551 and metoprolol competitively antagonized the effect of dobutamine with a K(B) of 2.84 nM and 609 nM, respectively. 6. Xamoterol had no stimulating effect on ICa. However, xamoterol competitively antagonized the stimulating effects of isoprenaline, salbutamol and dobutamine on ICa with a K(B) of 58-64 nM. 7. We conclude that a single population of receptors is involved in the beta-adrenoceptor-mediated regulation of ICa in frog ventricular myocytes. The pharmacological pattern of the response of ICa to the different beta-adrenoceptor agonists and antagonists tested suggests that these receptors are of the beta2-subtype.
Skeberdis
V A
VA
Laboratoire de Cardiologie Cellulaire et Moléculaire, INSERM U-446, Université de Paris-Sud, Faculté de Pharmacie, Chatênay-Malabry, France.
Jurevicius
J
J
Fischmeister
R
R
D000420:Albuterol / Q000494:pharmacology; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D020746:Calcium Channels, L-Type; D004280:Dobutamine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D009206:Myocardium / Q000378:metabolism*; D011412:Propanolamines / Q000494:pharmacology; D011893:Rana esculenta; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D017307:Xamoterol / Q000494:pharmacology
D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D011412:Propanolamines; D011943:Receptors, Adrenergic, beta; D004280:Dobutamine; C026777:ICI 118551; D017307:Xamoterol; D007545:Isoproterenol; D000420:Albuterol