Group I secreted PLA2 in the maintenance of human lower esophageal sphincter tone

Background & Aims: In cat spontaneous lower esophageal sphincter (LES), tone is maintained by the activity of group I secreted phospholipase A2 (sPLA2-I) that produces arachidonic acid. Arachidonic acid metabolites activate G proteins linked to phospholipases, producing second messengers and activation of a protein kinase C-dependent pathway to maintain tone. We examined the role of sPLA2-I in the maintenance of tone in human LES samples obtained from organ donors. Methods: In vitro LES tone and sPLA2-I-induced contraction of enzymatically isolated LES smooth muscle cells were measured in the absence or presence of inhibitors. Cell permeabilization by saponin allowed use of G-protein antibodies, Results: In vitro LES tone was reduced by inhibitors of sPLA2-I, by indomethacin, by the phosphatidylcholine-specific phospholipase C inhibitor D609, and by the protein kinase C inhibitor chelerythrine, sPLA2-I-induced contraction of isolated LES smooth muscle cells was reduced by indomethacin, pertussis toxin, Gi3 antibodies, D609, and by chelerythrine. Conclusions: Human LES tone is maintained by the activity of sPLA2-I that produces arachidonic acid and metabolites and activation of Gi3-linked receptors and of phosphatidylcholine-specific phospholipase C, resulting in production of diacylglycerol, activation of PHC, and maintenance of tone through a protein kinase C-dependent contractile pathway.