Contribution of Extracellular and Intracellular Calcium to the Enhanced Effect of an a-Adrenergic Agonist on Amylase Release from Dispersed Rat Parotid Cells

Abstract

The role of calcium in the potentiation of amylase release by the α-adrenergic agonist methoxamine (MTX) was examined using dispersed rat parotid acinar cells. The stimulatory effect of MTX (10 μM) on the β-adrenergic agonist isoproterenol (ISP, 1 μM)-induced amylase release was blocked by the α-adrenergic antagonist phentolamine (10 μM). In Ca-free (1 mM EGTA) medium, the increment of amylase release by MTX in normal medium was decreased by about 70%, but MTX still potentiated ISP-induced amylase release, MTX did not affect the cyclic AMP accumulation activated by ISP in either normal or Ca-free medium. MTX enhanced the ISP-stimulated uptake and efflux of 45Ca2+. These results suggest that both extracellular Ca2+ and intracellular stored Ca2+ may play an important role in the potentiation of amylase release from rat parotid acinar cells.