Cyclic ACP-ribose (cADPR). one of NAD metabolite was recently found to be able to release calcium from the microsome of sea urchin egg. In this study, NAD metabolite was observed to release calcium from the endoplasmic reticulum of mammalian cell line. Tratment of alkylating agents to cells reduced intracellular calcium concentration and these phenomena were prevented by ADPRT inhibitors such as 3-aminobenzidine (ABA) and thymidine. Alkylatng agents also lowered cellular $IP_3$ level, cellular protein kinase activity and phosphorylation of a 80Kd protein. a specific substrate for protein kinase C. These results suggest that alkylating-agent-initiated biological responses like the inhibition of DNA synthesis might be mediated by the reduction of intracellular calcium concentration.
