The role of calcium and cyclic AMP in amylase release from isolated rat parotid acinar cells: effect of calcium ionophore A23187.

The effect of the Ca ionophore A23187 on isoproterenol (ISP)-induced amylase release was investigated using isolated rat parotid acinar cells. A23187 increased amylase release in normal medium but this stimulated effect of A23187 was abolished in Ca-free medium. ISP-induced amylase release was inhibited by A23187 in Ca-free medium but not in normal medium. A23187 did not affect basal levels of cyclic AMP in normal medium or Ca-free medium but reduced the accumulation of cyclic AMP stimulated by ISP in both mediums. Both NaF- and ISP-stimulated activities of adenylate cyclase were reduced in washed membrane fraction prepared from A23187-treated slices of parotid glands. 45Ca2+ uptake stimulated by A23187 markedly increased, reached maximum at 10-20 min and then declined immediately. These results suggest that A23187 decreases the accumulation of cyclic AMP stimulated by ISP and results in an inhibition of ISP-induced amylase release in the absence of extracellular Ca2+, whereas a marked influx of Ca2+ stimulated by A23187 may possibly compensate the decrement of amylase release in the presence of extracellular Ca2+.