Somatostatin inhibits the nicotinic receptor-activated inward current in guinea pig chromaffin cells

Abstract At a holding potential of −60 mV, bath application of somatostatin produced no current response itself, but inhibited the nicotinic inward current, a concentration of about 0.01 μM being required for a half-maximal effect. This inhibition was affected neither by pretreatment with somatostatin nor by injection of guanosine-5′-0-(3-thiotriphosphate) through a pathch pipette. When somatostatin (0.03–0.1 μM) produced its maximum inhibition, the proportion of plateau to peak nicotinic current was greatly reduced (to 5.3±5.7 % from the control value of 34.9±4.9 %, n=5) with a facilitation of the time course of desensitization. After washout of somatostatin, the nicotinic current was restored to control level in a time-dependent, rather than an activation-dependent manner. The results suggest that somatostatin inhibits the function of the nicotinic receptor by facilitation of its desensitization or by an open-channel block.