Inositol trisphosphate-induced Ca2+ release from rat parotid subcellular fractions.

Inositol trisphosphate (IP3) has been shown to induce a release of sequestered calcium in a large (7,000-48,000 g) microsomal fraction isolated from rat parotid gland. This effect was also observed after the calcium uptake had been stopped by EGTA and thus was not the result of an inhibition of the active calcium transport. IP3-induced Ca2+ release was also demonstrated in a more purified microsomal fraction (16,000-48,000 g) apparently free of mitochondria, and in a fraction enriched in rough endoplasmic reticulum markers. These results support the hypothesis that IP3 may be a second messenger for intracellular calcium mobilization during stimulation of the parotid gland by calcium mobilising agonists.