Activation of Mouse Splenic Lymphocyte Guanylate Cyclase by Calcium Ion1

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Abstract
The guanosine 3', 5'-cyclic monophosphate (cGMP) level in the mouse splenic lymphocytes was increased about 2- to 3-fold by concanavalin A. This increase was completely dependent on the presence of Ca2+ in the medium. Homogenates of mouse splenic lymphocytes contained significant guanylate cyclase [EC 4.6.1.2] activity in both the 105, 000xg (60min) particulate and supernatant fractions and both fractions required Mn2+ for full activity. Calcium ion (3 mM) activated soluble guanylate cyclase 3-fold at a relatively low concentration of Mn2+ (less than 1 mM) but inhibited the particulate enzyme slightly at all Mn2+ concentrations tested. Concanavalin A itself did not stimulate either fraction of guanylate cyclase. Thus these results suggest that elevation of the cGMP level in lymphocytes by concanavalin A might be brought about by stimulation of Ca2+ uptake and activation of soluble guanylate cyclase by the latter.

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