Muscarinic stimulation of alpha 1E Ca channels is selectively blocked by the effector antagonist function of RGS2 and phospholipase C-beta 1

Neuronal alpha 1E Ca channel subunits are widely expressed in mammalian bra in, where they are thought to form R-type Ca channels. Recent studies have demonstrated that R-type channels contribute to neurosecretion and dendriti c Ca influx, but little is known concerning their modulation. Here we show that alpha 1E channels are strongly stimulated, and only weakly inhibited, through M1 muscarinic acetylcholine receptors. Both forms of channel modula tion are mediated by pertussis toxin- insensitive G-proteins. Channel stimu lation is blocked by regulator of G-protein signaling 2 (RGS2) or the C-ter minal region of phospholipase C-beta 1 (PLC beta 1ct), which have been prev iously shown to function as GTPase- activating proteins for G alpha q. In c ontrast, RGS2 and PLC beta 1ct do not block inhibition of alpha 1E through M1 receptors. Inhibition is prevented, however, by the C-terminal region of beta-adrenergic receptor kinase 1, which sequesters G beta gamma dimers. T hus, stimulation of alpha 1E is mediated by a pertussis toxin-insensitive G alpha subunit (e.g., G alpha q), whereas inhibition is mediated by G beta gamma. The ability of RGS2 and PLC beta 1ct to selectively block stimulatio n indicates these proteins functioned primarily as effector antagonists. In support of this interpretation, RGS2 prevented stimulation of alpha 1E wit h non-hydrolyzable guanosine 5'-0-( 3-thiotriphosphate). We also report str ong muscarinic stimulation of rbE-II, a variant alpha 1E Ca channel that is insensitive to voltage-dependent inhibition. Our results predict that G al pha q-coupled receptors predominantly stimulate native R-type Ca channels. Receptor-mediated enhancement of R-type Ca currents may have important cons equences for neurosecretion, dendritic excitability, gene expression, or ot her neuronal functions.