Calcium Uptake in Rat Parotid Gland Secretory Granules

Abstract

45Ca2+uptake in isolated rat parotid secretory granules was examined in the presence of oxalate. Uptake of calcium was dependent on time, with the maximum occurring at 15 min. The uptake of calcium was dependent on adenosine-5'-triphosphate (ATP), and substitution of ATP with B,g-methylene-ATP did not stimulate calcium uptake. Enzyme marker analysis indicated that mitochondria accounted for no greater than 3.0 ±0.2% of the observed ATP-dependent calcium uptake. Calcium uptake was blocked by the ATPase inhibitors tributyltin, IC50= 12.2 ±0.6 nmol/L and 4-acetamido-4'-isothiocyano-2,2'-stilbene disulphonic acid (SITS), IC50= 3.0 ±0.3 (μmol/L. These results indicate that in the parotid secretory granule there is a calcium uptake mechanism that is dependent on the hydrolysis of ATP and is suppressed by two inhibitors of granule ATPase.