Inhibitory effect of carbachol on isoproterenol-induced amylase release from isolated rat parotid cells.

The effect of carbachol (CCh) on isoproterenol (ISP)-induced amylase release was investigated using isolated rat parotid cells. CCh (1-100 microM) inhibited ISP (1 microM)-induced amylase release in a dose-dependent manner, whereas CCh alone had a slightly increasing effect on amylase release. Both inhibitory and stimulatory effects of CCh were blocked by atropine (10 microM), and they also disappeared in Ca-free (1 mM EGTA) medium. CCh (10 microM) did not change cyclic AMP levels induced by ISP (1 microM), but significantly inhibited dibutyryl cyclic AMP (1 microM)-induced amylase release. CCh and ISP increased 45Ca2+ uptake in 30 min. Furthermore, 45Ca2+ uptake in the presence of CCh plus ISP increased almost additively. These increasing effects of CCh were abolished by atropine. Calcium ionophore A23187 (10 microM) inhibited ISP-induced amylase release to the level of the release by A23187 alone and considerably increased 45Ca2+ uptake. CCh increased both control and ISP-stimulated effluxes of 45Ca2+ in Ca-free (1 mM EGTA) medium from parotid cells. These results suggest that CCh produces a potent increase in Ca2+ influx from the extracellular medium into parotid cells, and this increase may result in a higher level of cytosolic free Ca2+ which inhibits the ISP-induced amylase release.