Cyclic GMP metabolism in macrophages: I. Regulation of cyclic GMP levels by calcium and stimulation of cyclic GMP synthesis by NO-generating agents

Abstract

Levels of guanosine 3′,5′-cyclic monophosphate (cGMP) were determined by radioimmunoassay in adherence-purified, oil-induced guinea pig peritoneal exudate macrophages, after extraction of the cells with perchloric acid, purification on Dowex AG1-X8, and acetylation. We found that: (i) Basal cGMP levels were strictly dependent on the concentration of extracellular Ca 2+ (0.33 ± 0.03 pmol/mg macrophage protein in Ca 2+-free medium and 2.49 ± 0.42 pmol/mg in 1.8 m M Ca 2+). (ii) The stimulatory effect of Ca 2+ on cGMP levels was prevented by tetracaine. (iii) The cGMP content of macrophages was not elevated by incubation with the ionophore A23187 at extracellular Ca 2+ concentrations varying between 0 and 1.8 m M. (iv) Macrophage cGMP levels were increased markedly (up to 40-fold) by incubation of the cells with the nitric oxide (NO)-generating agents, sodium azide, hydroxylamine, sodium nitrite, and sodium nitroprusside. (v) Stimulation of cGMP accumulation by NO-generating agents occurred within 30 sec, was Ca 2+-independent, and developed in the presence and absence of the phosphodiesterase inhibitor, isobutyl-methylxanthine. (vi) A minimal elevation in the macrophage cGMP level (less than 2-fold) was induced by ascorbic acid but no significant increases were induced by the following agents, found effective in other cells: serotonin, acetylcholine, carbamylcholine, phorbol myristate acetate, arachidonic acid, Superoxide dismutase, and nitrate reductase.