PHOSPHOLIPASE-C-INDUCED ANION SECRETION AND ITS INTERACTION WITH CARBACHOL IN THE RAT COLONIC MUCOSA

Phospholipase C (PLC) from clostridium perfringens induced a biphasic increase in short-circuit current (Isc) in the rat colon. The Isc rose rapidly to a transient peak, before it increased again to a plateau lasting for several hours. Ion replacement experiments and sensitivity to furosemide or a Cl- channel blocker indicated that PLC induced Cl- secretion. The first peak was suppressed by indomethacin, indicating mediation by prostaglandins. In contrast, the second phase was only partially sensitive to the cyclooxygenase blocker. The long-time action of PLC was dependent on intra- and extracellular Ca2+, although PLC did not induce an increase in the intracellular Ca2+ concentration of the enterocytes. The effect of PLC was blocked by the protein kinase inhibitor, staurosporine. Carbachol, when added during the second phase of the PLC response, induced a 'paradox' change in Isc: a rapid, transient increase in Isc was followed by a long-lasting decrease. This inhibition of the PLC response was more pronounced after elevation of the external Ca2+ concentration. A Ca2+ ionophore, ionomycin, and a Ca2+ channel activator, BAY K 8644, also inhibited the PLC response. The results suggest dual dependence of the action of PLC on the intracellular Ca2+ concentration.