Formation of extracellular cGMP in blood mononuclear and platelet cell preparations

The addition of inorganic acids to cell suspensions of mononuclear cells and platelets significantly increased concentrations of cGMP in supernatant fractions (3-6 X basal level). Increases in supernatant cGMP with the addition of 10(-4) M adrenaline (19 X basal level) 10(-5) M 5-HT (33 X) and 5 mM ascorbic acid (38 X) were detectable after acidification of the cell suspensions. Agonist and acid concentrations at termination of the incubations were important in determining cGMP concentrations in supernatants. The results suggest that cGMP is formed on the exterior surface of the cell membrane and therefore has an extracellular, rather than intracellular, role in transmission of the membrane stimulus for cell activation.