Stimulation of forskolin of intact S49 lymphoma cells involves the nucleotide regulatory protein of adenylate cyclase.

Abstract

We have used wild type 549 lymphoma cells and S49 variants that have lesions in their ability to generate CAMP to explore the mechanism of activation of adenylate cyclase by the diterpene forskolin.In intact wild type cells, forskolin rapidly and reversibly stimulated CAMP accumulation several hundred-fold over basal levels.Simultaneous addition of forskolin and the padrenergic agonist isoproterenol gave greater than additive (Le.synergistic) responses.Forskolin lowered the Kact for isoproterenol-stimulated CAMP accumulation 2-to %fold and increased maximal response to isoproterenol 8-to 10-fold; isoproterenol decreased the K,,, for forskolin about 10-fold but had a much smaller effect (t2-fold) on maximal response.In competitive binding studies between (-)isoproterenol and [1261]iodocyanopindolol, forskolin more than doubled the fi-action of /%adrenergic receptors in a high affinity (-5-10