[Changes in Ca2+ level in cytoplasm of rat thymocytes after treatment with mitogens]

Mitogen-induced changes in free Ca2+ concentration in the cytoplasm [Cai2+] of rat thymocytes were studied with the use of quin-2, a Ca2+-sensitive fluorescent indicator. Concanavalin A (Con A) and phytohemagglutinin were shown to increase [Cai2+] from 150 +/- 10 nM for the resting cells up to the value of 380 +/- 10 nM. This increase in [Cai2+] depended on the mitogen concentration. It was observed both in the presence of 1 mM external Ca2+ and in the Ca2+ free medium. The Con A-induced increase of [Cai2+] was not abolished by Na+ removal from the medium or by verapamil, an inhibitor of potential-dependent Ca2+ channels. Hence, the increase in Cai2+ was not due to an activation of potential operated Ca2+-channels. Agents which raise intracellular cAMP blocked Con A-induced increase of [Cai2+].