A CA2-INDEPENDENT RECEPTOR FOR ALPHA-LATROTOXIN, CIRL, MEDIATES EFFECTS ON SECRETION VIA MULTIPLE MECHANISMS()

alpha-Latrotoxin (alpha-Ltx), a component of black widow spider venom, stimulates secretion from nerve terminals and from PC12 cells. In thi s study we examine the effects of expression of a newly cloned Ca2+-in dependent receptor for alpha-Ltx (GIRL) on secretion from bovine chrom affin cells. We first characterized the effect of alpha-Ltx on secreti on from untransfected cells, alpha-Ltx, by binding in a Ca2+-independe nt manner to an endogenous receptor, causes subsequent Ca2+-dependent secretion from intact cells. The stimulation of secretion is correlate d with Ca2+ influx caused by the toxin. In permeabilized cells in whic h the Ca2+ concentration is regulated by buffer, alpha-Ltx also enhanc es Ca2+-dependent secretion, indicating a direct role of the endogenou s receptor in the secretory pathway. Expression of GIRL increased the sensitivity of intact and permeabilized cells to the effects of alpha- Ltx, demonstrating that this protein is functional in coupling to secr etion. Importantly, in the absence of alpha-Ltx, the expression of CIR L specifically inhibited the ATP-dependent component of secretion in p ermeabilized cells without affecting the ATP-independent secretion, Th is suggests that this receptor modulates the normal function of the re gulated secretory pathway and that alpha-Ltx may act by reversing the inhibitory effects of the receptor.