INVOLVEMENT OF CALMODULIN IN THE ACTIVATION OF STORE-OPERATED CA2+ ENTRY IN RAT HEPATOCYTES

The possible participation of calmodulin in the activation of store-op erated Ca2+ entry (SOC) in single rat hepatocytes was investigated mic rospectrofluorimetrically. SOC was triggered after discharging intrace llular Ca2+ stores using the endoplasmic reticulum Ca2+-ATPase inhibit or thapsigargin in the absence of external Ca2+. Re-admission of bath Ca2+ caused a rapid and pronounced Ca2+ entry. The calmodulin antagoni sts calmidazolium or CGS 9343B applied before the thapsigargin treatme nt inhibited SOC, whereas they were ineffective when added after the t hapsigargin-induced Ca2+ transient. This study suggests that activatio n of calmodulin after the elevation of cytosolic Ca2+ associated with the emptying of Ca2+ stores is involved in the triggering of SOC in he patocytes. (C) 1998 Federation of European Biochemical Societies.