Role of phosphatidic acid in carbachol-induced contraction in guinea pig Taenia coli.

Carbachol (CCh, 10(-8)-10(-4) M) increased in concentration-dependent manner the mass of phosphatidic acid (PA), but not the mass of diacylglycerol (DG) in the Taenia coli from guinea pig. The increase in the amount of PA caused by CCh was maintained for 20 min. Release of choline from choline phospholipids labeled with [methyl-3H]choline was not changed by CCh. A DG kinase inhibitor, R59022, inhibited the CCh-induced increase in the mass of PA. These results indicate that the increase in the mass of PA by CCh is due to immediate phosphorylation by DG kinase to PA, of the DG produced by phospholipase C (PLC). It is not due to formation of PA by the direct action of phospholipase D. CCh increased 45Ca2+ uptake into the tissue. R59022 inhibited the sustained phase of CCh-induced contraction and 45Ca2+ uptake into the tissue, but only slightly inhibited the initial phase of the CCh-induced contraction. This inhibition by R59022 may result from the inhibitory effect on the CCh-induced increase in PA. These results suggest that CCh activates both PLC and DG kinase and the resultant increase in the mass of PA contributes to the regulation of the sustained phase of CCh-induced contraction which is related to Ca2+ influx.