FUNCTIONAL DEACTIVATION OF THE MAJOR NEURONAL NICOTINIC RECEPTOR CAUSED BY NICOTINE AND A PROTEIN-KINASE C-DEPENDENT MECHANISM

The effect of nicotine on the major human neuronal nicotinic receptor (alpha 4 beta 2 subtype) was studied in permanently transfected HEK 29 3 cells. Prolonged exposure to low concentrations of nicotine(1 mu M) increased epibatidine binding but functionally deactivated the nicotin ic receptor, abolishing Ca2+ influx in response to an acute nicotine c hallenge. Deactivation could also be caused by down-regulating protein kinase C (PKC) activity with 0.5 mu M phorbol-12,13-dibutyrate or bri efly incubating cells with the PKC inhibitor NPC-15437. Recovery from receptor deactivation caused by either nicotine treatment or PKC inhib ition occurred slowly (4-6 hr). Reversal of nicotine-induced deactivat ion was accelerated by the addition of inhibitors of protein phosphata ses 2A and 2B. These data suggest a hypothetical mechanism of nicotine -induced deactivation that involves dephosphorylation of nicotinic rec eptors at PKC phosphorylation sites.