NOREPINEPHRINE BLOCKS A CALCIUM CURRENT OF ADULT-RAT SYMPATHETIC NEURONS VIA AN ALPHA-2-ADRENOCEPTOR

The effects of α-adrenoceptor agonist and antagonist drugs on the Ca2+ current of acutely isolated adult rat superior cervical ganglion (SCG) neurons were investigated to characterize the adrenoceptor which mediates a catecholamine-induced decrease of the Ca2+ current. Ca2+ currents were recorded using the whole-cell variant of the patch-clamp technique from neurons isolated enzymatically from adult rat SCG. Norepinephrine (1 μM) produced a rapid, reversible, and concentration-dependent decrease in Ca2+ current amplitude and slowed the rising phase of the Ca2+ current. These effects could be mimicked by clonidine (1 μM), an α2-gonist but not by the α1-agonist phenylephrine (1 μM). The norepinephrine-induced decrease in Ca2+ current amplitude was attenuated in the presence of idazoxan (1 μM), an α2-antagonist, but was unaffected in the presence of the α1-antagonist prazosin (1 μM). Neither antagonist displayed any Ca2+ current blocking activity. These results suggest that the α-receptor which mediates the norepinephrine-induced decrease of the Ca2+ current in adult rat SCG neurons is of the α2-subtype. © 1990.