Cardiac L-type Ca²⁺ channels can be stimulated by activation of ₂-adrenoceptors. We intended to determine how the gating behavior at the single-channel level (cell-attached configuration) is affected after selective stimulation of ₂-adrenoceptors. Rat cardiomyocytes were exposed to zinterol, a ₂-agonist (n = 7), isoproterenol (n = 6), a nonselective agonist, 8-bromo-cAMP (n = 6), and a combination of isoproterenol and ICI-118551 (n = 8), a selective ₂-receptor antagonist, or isoproterenol and CGP-20712A, a ₁-selective antagonist (n = 7). In all groups the ensemble-average current and the availability of the channels to open on depolarization were increased in a similar fashion. In addition, the open probability (P_o) within active sweeps was elevated. However, zinterol exerted this effect in a unique manner. It elevated P_o not by shortening closed times but solely by reducing active sweeps with very low P_o and a short burst duration. All zinterol effects were abolished by ICI-118551 (n = 5) and mimicked by isoproterenol plus CGP-20712A (n = 7). We conclude that ₂-adrenoceptor activation of L-type channels differs qualitatively from the classical cAMP-dependent mechanism.

single L-type channels; rat ventricular myocytes; zinterol

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