A protein kinase C-dependent mechanism(s) is involved in atropine-resistant accumulation of diacylglycerol in rat parotid gland.

We investigated the atropine-resistant accumulation of sn-1,2-diacylglycerol (DAG) on stimulation of 1 microM carbachol (CCh) in parotid acinar cells. CCh-induced DAG accumulation was biphasic, peaking at 5 and 20 min. Atropine inhibited two peaks in a dose-dependent manner, but the first peak was inhibited much more than the second one. Atropine (10 microM) completely inhibited both DAG accumulation and the breakdown of phosphatidylinositol 4-monophosphate and 4,5-bisphosphate (PIP2) 5 min after stimulation with CCh. In contrast, the breakdown of PIP2 at 20 min was completely inhibited by 10 microM atropine, but DAG accumulation was not. This atropine-resistant component at 20 min is significantly inhibited by staurosporine, a protein kinase C inhibitor. These results suggest that atropine-resistant accumulation of DAG at 20 min derives directly from other lipids rather than phosphoinositides and is regulated by a protein kinase C-dependent mechanism(s).