NICOTINIC RECEPTORS ARE REGULATED BY PROTEIN-KINASE-C ACTIVATED VIA ANICOTINIC RECEPTORS-MEDIATED SIGNALING PATHWAY

The present study was conducted to examine the effect of protein kinas e C (PKC) on nicotinic acetylcholine (ACh) receptors expressed in Xeno pus oocytes by monitoring single-channel currents. In an outside-out p atch-clamp configuration, ACh (1 mu M) elicited single channel current s with a slope conductance of 31 pS (control) in normal Torpedo ACh re ceptors. Activation of PKC via an endogenous phosphatidylinositol sign aling pathway elevated the slope conductance to 41 pS, which effect wa s blocked by the selective PKC inhibitor, staurosporine. Mutant ACh re ceptor channels, which mimic PKC phosphorylation of the receptors, exh ibited a slope conductance of 41 pS. Notably, pretreatment with a high er concentration of ACh (100 mu M) caused an increase in the slope con ductance of the channels for 1 mu M ACh (43 pS), which was the same le vel as obtained with either PKC activation or mutant ACh receptors, an d this effect was also inhibited by staurosporine. In addition, the co ntrol slope conductance was reduced by PKC inhibitor peptide (24 pS), which corresponded to that obtained with another mutant ACh receptors lacking PKC phosphorylation sites (18 pS). Mouse muscle ACh receptors were also regulated by the same mechanism. The results of the present study suggest that ACh activates PKC via nicotinic ACh receptors, whic h alternatively, modulates the properties of the receptor channels. (C ) 1998 Elsevier Science B.V. All rights reserved.