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 Ca2+ mobilization in the human submandibular cell line A253 were studied. Exposure of A253 cells to fetal bovine serum (FBS) elicited a 3.3‐fold increase in IP3 formation and a concentration‐dependent transient increase in cytosolic free Ca2+ concentration ([Ca2+]i), which was similar in Ca2+‐containing and Ca2+‐free media. Newborn bovine serum (NBS), but not bovine serum albumin (BSA), induced a similar response. The Ca2+ release triggered by FBS was significantly (88%) reduced by the phospholipase C inhibitor U73122, indicating that Ca2+ release induced by FBS is through the PLC pathway. Pretreatment with the tyrosine kinase inhibitor genistein abolished the FBS‐ and NBS‐induced Ca2+ release, suggesting that tyrosine kinase plays an important role in mediating the Ca2+ release. Pre‐exposure to ATP or thapsigargin (TG) significantly reduced the FBS‐induced [Ca2+]i increase, indicating that Ca2+ release caused by FBS is from the TG‐ or ATP‐sensitive Ca2+ store. 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 TG. 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+ influxes including the store depletion‐activated Ca2+ influx. J. Cell. Biochem. 73:458–468, 1999. © 1999 Wiley‐Liss, Inc.