LEUKOTRIENE D-4-INDUCED CONTRACTION OF CAT ESOPHAGEAL AND LOWER ESOPHAGEAL SPHINCTER CIRCULAR SMOOTH-MUSCLE

Background & Aims: In esophageal circular muscle, acetylcholine activa tes phosphatidylcholine-specific phospholipases C and D and phospholip ase A(2), producing diacylglycerol and arachidonic acid, which cause c ontraction by interacting synergistically to activate protein kinase C . In a model of acute esophagitis, leukotriene D-4 (LTD4) contributes to acetylcholine-induced contraction. We examined intracellular signal ing in LTD4-induced contraction. Methods: Esophageal and lower esophag eal sphincter (LES) cells, isolated by enzymatic digestion, were contr acted by CTD, in the absence or presence of inhibitors. Permeabilizati on by saponin allowed use of G-protein antibodies and heparin. Results : Esophageal contraction was inhibited by pertussis toxin, G(i3) antib odies, D609 (phosphatidylcholine-specific phospholipase C inhibitor), propranolol (phospholipase D pathway inhibitor), and chelerythrine (pr otein kinase C antagonist) but not W7 (calmodulin antagonist). LES con traction was unaffected by pertussis toxin, It was inhibited by G(q) a ntibodies, U-73122 (phosphatidylinositol-specific phospholipase C inhi bitor), heparin (inositol 1,4,5-trisphosphate inhibitor), and W7 and r educed by D609. Conclusions: In the esophagus, LTD4 activates a protei n kinase C-dependent pathway through pertussis toxin-sensitive G(i3) p roteins and phosphatidylcholine-specific phospholipase, In the LES, LT D4 activates a calmodulin-dependent pathway through pertussis toxin-in sensitive G(q) proteins and phosphatidylinositol-specific phospholipas e C. The intracellular pathways activated by LTD4 in the esophagus and the LES are similar to those activated by acetylcholine and other ago nists.