Histamine and calcium are independently regulated intracellular mediators of lymphocyte mitogenesis

In addition to cytosolic calcium ([Ca2+]i), intracellular histamine has been implicated as a mediator of mitogenesis in normal mouse spleen cells stimulated by the plant lectin, concanavalin (Con) A. We have linked the growth-promoting action of this amine with its binding to distinct intracellular sites, designated HIC, in microsomes and nuclei and shown that the proliferative response of lymphocytes can be blocked by antagonizing the binding of histamine to HIC by N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine.HCl (DPPE), or by depleting intracellular histamine levels by the specific irreversible inhibitor of histidine decarboxylase, alpha-FMH. We now demonstrate that, at a concentration which completely inhibits both 3H-histamine binding to HIC and 3H-thymidine incorporation into DNA, DPPE fails to block the acute (30 seconds) rise in [Ca2+]i in spleen cells exposed to Con A. Conversely, the calcium channel antagonist, verapamil, suppresses the Con A-induced rise in [Ca2+]i at a concentration which correlates with its inhibition of thymidine incorporation into DNA, but does not prevent histamine synthesis or bind to HIC. Thus, in Con A-stimulated lymphocytes, intracellular histamine and calcium appear to be independently regulated, but essential, mediators of the proliferative response.