Activation of tyrosine hydroxylase by pituitary adenylate cyclase-activating polypeptide (PACAP-27) in bovine adrenal chromaffin cells.

The effect of pituitary adenylate cyclase-activating polypeptide (PACAP-27) on tyrosine hydroxylase activity has been studied in intact, cultured, bovine adrenal chromaffin cells. Tyrosine hydroxylase activity was determined in situ by measuring the production of 14CO2 following the hydroxylation and rapid decarboxylation of [14C]tyr offered to the cells. PACAP-27 increased tyrosine hydroxylase activity 3-fold over 10 min. With an EC50 of 10-20 nM. PACAP-38 was approximately 2-fold less potent. Removing extracellular Ca2+ reduced basal tyrosine hydroxylase activity and the activation produced by both PACAP-27 and forskolin by about 20%. In the absence of extracellular Ca2+, chelation of intracellular Ca2+ by treating cells with BAPTA-AM (50 microM) caused a consistent 40-50% reduction in basal tyrosine hydroxylase activity and in the responses to forskolin and PACAP-27. The tyrosine hydroxylase activation produced by PACAP-27 was unaffected by the protein kinase C inhibitor Ro 3l-8220 (3 microM), but was reduced by 85% by the protein kinase A inhibitor H89 (10 microM). PACAP-27 increased cellular cyclic AMP levels 3-fold at 100 nM. The results suggest that PACAP-27 activates tyrosine hydroxylase in bovine chromaffin cells through cyclic AMP formation and protein kinase A activation, and that both extracellular and intracellular Ca2+ modulate the effect of the adenylate cyclase/cyclic AMP/protein kinase A signalling pathway on tyrosine hydroxylase activity.