Stimulation of murine B cells by the combination of calcium ionophore plus phorbol ester

The ability of calcium ionophore and phorbol ester to stimulate entry into S phase was assessed during short-term cultures of murine B cells extensively depleted of T cells. Neither ionomycin alone nor PMA alone stimulated DNA synthesis. However, the combination of ionomycin plus PMA acted in synergy to induce initiation of DNA synthesis in murine B cells. A role for protein kinase C was implied by the inability of 4 alpha-phorbol didecanoate to reproduce the effects of PMA. The combination of ionomycin plus PMA also stimulated DNA synthesis in xid-defective B cells.