Murine ventricular L-type Ca(2+) current is enhanced by zinterol via beta(1)-adrenoceptors, and is reduced in TG4 mice overexpressing the human beta(2)-adrenoceptor

• Published in: British journal of pharmacology 2001-05, Vol.133 (1), p.73-82
• Main Authors: Heubach, J F, Graf, E M, Molenaar, P, Jäger, A, Schröder, F, Herzig, S, Harding, S E, Ravens, U
• Format: Article
• Language: English
• Subjects: Adrenergic beta-1 Receptor Agonists; Adrenergic beta-2 Receptor Agonists; Adrenergic beta-Agonists - pharmacology; Adrenergic beta-Antagonists - pharmacology; Animals; Barium - metabolism; Binding Sites; Calcium - metabolism; Calcium Channels, L-Type - metabolism; Electric Conductivity; Ethanolamines - pharmacology; GTP-Binding Protein alpha Subunits, Gi-Go - metabolism; Heart Ventricles - cytology; Heart Ventricles - drug effects; Heart Ventricles - metabolism; Humans; Imidazoles - pharmacology; Ion Channel Gating - drug effects; Isoproterenol - antagonists & inhibitors; Isoproterenol - pharmacology; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Myocardium - cytology; Myocardium - metabolism; Pertussis Toxin; Propanolamines - pharmacology; Protein Binding; Receptors, Adrenergic, beta-1 - metabolism; Receptors, Adrenergic, beta-2 - genetics; Receptors, Adrenergic, beta-2 - metabolism; Virulence Factors, Bordetella - pharmacology
• ISSN: 0007-1188

1. The functional coupling of beta(2)-adrenoceptors (beta(2)-ARs) to murine L-type Ca(2+) current (I(Ca(L))) was investigated with two different approaches. The beta(2)-AR signalling cascade was activated either with the beta(2)-AR selective agonist zinterol (myocytes from wild-type mice), or by spontaneously active, unoccupied beta(2)-ARs (myocytes from TG4 mice with 435 fold overexpression of human beta(2)-ARs). Ca(2+) and Ba(2+) currents were recorded in the whole-cell and cell-attached configuration of the patch-clamp technique, respectively. 2. Zinterol (10 microM) significantly increased I(Ca(L)) amplitude of wild-type myocytes by 19+/-5%, and this effect was markedly enhanced after inactivation of Gi-proteins with pertussis-toxin (PTX; 76+/-13% increase). However, the effect of zinterol was entirely mediated by the beta(1)-AR subtype, since it was blocked by the beta(1)-AR selective antagonist CGP 20712A (300 nM). The beta(2)-AR selective antagonist ICI 118,551 (50 nM) did not affect the response of I(Ca(L)) to zinterol. 3. In myocytes with beta(2)-AR overexpression I(Ca(L)) was not stimulated by the activated signalling cascade. On the contrary, I(Ca(L)) was lower in TG4 myocytes and a significant reduction of single-channel activity was identified as a reason for the lower whole-cell I(Ca(L)). The beta(2)-AR inverse agonist ICI 118,551 did not further decrease I(Ca(L)). PTX-treatment increased current amplitude to values found in control myocytes. 4. In conclusion, there is no evidence for beta(2)-AR mediated increases of I(Ca(L)) in wild-type mouse ventricular myocytes. Inactivation of Gi-proteins does not unmask beta(2)-AR responses to zinterol, but augments beta(1)-AR mediated increases of I(Ca(L)). In the mouse model of beta(2)-AR overexpression I(Ca(L)) is reduced due to tonic activation of Gi-proteins.