Effects of serum on calcium mobilization in the submandibular cell line A253

The effects of serum on inositol 1,4,5-trisphosphate (IP3) formation and Ca 2+ mobilization in the human submandibular cell line A253 were studied. Exp osure of A253 cells to fetal bovine serum (FBS) elicited a 3.3-fold increas e in IP3 formation and a concentration-dependent transient increase in cyto solic free Ca2+ concentration ([Ca2+](i)), which was similar in Ca2+-contai ning and Ca2+-free media. Newborn bovine serum (NBS), but not bovine serum albumin (BSA), induced a similar response. The Ca2+ release triggered by FB S was significantly (88%) reduced by the phospholipase C inhibitor U73122, indicating that Ca2+ release induced by FBS is through the PLC pathway. Pre treatment with the tyrosine kinase inhibitor genistein abolished the FBS- a nd NBS-induced Ca2+ release, suggesting that tyrosine kinase plays an impor tant role in mediating the Ca2+ release. Pre-exposure to ATP or thapsigargi n (TC) significantly reduced the FBS-induced [Ca2+](i) increase, indicating that Ca2+ release caused by FBS is from the TG- or ATP-sensitive Ca2+ stor e. While FBS exposure elicited a large Ca2+ release, it reduced Ca2+ influx . Furthermore, FBS significantly inhibited the Ca2+ influx activated by the depletion of intracellular stores by ATP or TC. These results suggest that (1) serum elicits Ca2+ release from ATP- and TG-sensitive stores, which is mediated by IP3; (2) the serum-induced Ca2+ release may be modulated by a tyrosine kinase-associated process; and (3) serum strongly inhibits Ca2+ in fluxes including the store depletion-activated Ca2+ influx. (C) 1999 Wiley- Liss, Inc.