Effect of calcium on the cyclic GMP elevation induced by thymosin fraction 5

Thymosin fraction 5 induces an increase in cyclic GMP but not cAMP in murine thymocytes. Calcium (0.6 mM) is necessary for an optimal response in both phosphate buffered saline and hepes-buffered RPMI 1640 media. The calcium dependence of the cGMP response was most pronounced in a minimal salts medium (PBS) and higher concentrations (greater than 0.8 mM) caused a lessening of the cGMP elevation induced by thymosin. Basal cGMP levels of thymus and spleen lymphocytes vary with increasing concentrations of calcium (0–1 mM) and to a lesser extent, the levels of cAMP also are increased. Calcium uptake was measured both at mitogenic levels of Con A and at thymosin concentrations which were similar to those necessary for the increase in cGMP. The results suggest that calcium and cGMP play an important role in T cell differentiation under the influence of thymosin.