Catecholamine-mediated elevation of cyclic GMP in the rat C-6 glioma cell line.

Catecholamines cause an elevation of both cyclic GMP and cyclic AMP levels in the rat C-6 glioma cell line. The response is mediated by a beta-receptor, with a Ka for stimulation of cyclic GMP of 2.6 X 10(-7)M. Maximum levels of cyclic GMP are reached by 5 min. whereas cyclic AMP levels are maximal by 10 min. Removal of calcium decreases the cyclic GMP elevation by 60%. Refractoriness to a second treatment with catecholamine develops for both responses. Catecholamine sensitivity of the cyclic GMP-generating system appears in the cells only as they start to contact and enter the stationary growth phase. In contrast to the effects of catecholamines, cholinergic agonists have no effect on either cyclic GMP or cyclic AMP levels.