Reactive oxygen species (H2O2):: effects on the gallbladder muscle of guinea pigs

Reactive oxygen species (ROS) have been implicated in the pathogenesis of muscle dysfunction in acute inflammatory processes. The aim of these studies was to determine the effects of ROS on gallbladder muscle function in vitro. Single muscle cells were obtained by enzymatic digestion. H2O2 (70 muM) caused maximal contraction of up to 14% and blocked the response to CCK-8, ACh, and KCl. It did not affect the contractions induced by guanosine 5'-O-(3-thiotriphosphate), diacylglycerol, and inositol 1,4,5-trisphosphate that circumvent membrane receptors. The contraction induced by H2O2 was inhibited by AACOCF(3) [cytosolic phospholipase A(2) (cPLA(2)) inhibitor], indomethacin (cyclooxygenase inhibitor), chelerythrine [protein kinase C (PKC) inhibitor], or PD-98059 [mitogen-activated protein kinase (MAPK) inhibitor]. H2O2 also reduced the CCK receptor binding capacity from 0.36+/-0.05 pmol/mg protein (controls) to 0.17+/-0.03 pmol/mg protein. The level of lipid peroxidation as well as the PGE(2) content was significantly increased after H2O2 pretreatment. Unlike superoxide dismutase, the free radical scavenger catalase prevented the H2O2 induced contraction, and its inhibition of the CCK-8 induced contraction. It is concluded that ROS cause damage to the plasma membrane of the gallbladder muscle and contraction through the generation of PGE(2) induced by cPLA(2)-cyclooxygenase and probably mediated by the PKC-MAPK pathway.