PROTEIN-KINASE A REGULATES NICOTINIC CHOLINERGIC RECEPTORS AND SUBUNIT MESSENGER RIBONUCLEIC-ACIDS IN PC-12 CELLS

To delineate mechanisms regulating the expression of neuronal nicotini c cholinergic receptors (nAcChRs), we studied the cAMP-dependent secon d messenger system. PC 12 cells were grown in (Bu)(2)cAMP (0.001-1.0 m M) or vehicle for 7 days, and specific [H-3] nicotine binding was meas ured. (Bu)(2)cAMP (0.1 mM) increased specific binding 2- and 4-fold at 3 and 7 days, respectively, whereas 1.0 mM enhanced binding 4-fold at both time intervals. Cells grown in 8-bromo-cAMP (1.0 mM) showed a a- fold increase in [H-3]nicotine binding at 3 days. Forskolin (10-100 mu M), in combination with isobutyl-methylxanthine (1.0 mM), enhanced [H -3]nicotine binding 2- to 3-fold at 7 days; forskolin or isobutyl-meth ylxanthine alone had no effect. Specific [H-3] nicotine binding to PC 12 cell mutants (A126.1B2 and A123.7), deficient in cAMP-responsive pr otein kinase A types I and II, were unaffected by (Bu)(2)cAMP. Norther n gel analysis of nAcChR subunit messenger RNAs showed that the alpha- 3, alpha-5, and beta-4 subunits were significantly decreased by (Bu)(2 )cAMP at 4 h. However, (Bu)(2)cAMP caused an increase in the beta-2 me ssenger RNA transcript at 4 h, which returned to baseline by 24 h. The se studies indicate that the cAMP-protein kinase A system regulates ex pression of nAcChR by PC 12 cells. These studies also suggest that enh ancement of [H-3]nicotine binding by activated protein kinase A may no t involve synthesis of new receptor subunit proteins.