Phosphatidic acid-induced contraction in guinea-pig taenia coli

: Natural phosphatidic acid from egg yolk lecithin (PA) caused a sustained contraction in guinea-pig taenia coli. The contractile response to PA was concentration-dependent (10(-6)-10(-4) M) in the normal medium and the maximal response to PA was about 20% of the response to carbachol (CCh) at 10(-6) M. Phospholipase D mimicked PA-induced contraction. This result suggests that increase in endogenous PA can induce contraction. The PA-induced contraction was not inhibited by atropine (10(-6) M). The contraction was more dependent on concentration of extracellular Ca2+ than CCh-induced contraction. PA increased 45Ca2+ uptake into the tissue. These results suggest that the PA-induced contraction results from increase in Ca2+ influx across plasma membranes, but not release of Ca2+ from intracellular stores in guinea-pig taenia coli. The PA-induced contraction was inhibited to 42% of the control response by propyl gallate (0.2 mM), a combined inhibitor of cyclooxygenase and lipoxygenase. This result indicates that a portion of the contraction is related to release of arachidonic acid and its metabolites, and the other portions are based on direct action of PA. These results suggest a possibility that increased PA by agonist stimulation is related to the following extracellular Ca2(+)-dependent contraction.