Submitted on May 1, 2003
Accepted on July 16, 2003
PAF-LIKE LIPIDS- AND PAF-INDUCED GALLBLADDER (GB) MUSCLE CONTRACTION IS MEDIATED BY DIFFERENT PATHWAYS IN GUINEA PIGS
Michele P. L. Guarino1, Zuo-Liang Xiao1, Piero Biancani1, and Jose Behar1*
1 Department of Medicine, Rhode Island Hospital and Brown University School of Medicine, Providence, RI, USA
* To whom correspondence should be addressed. E-mail: Jose_Behar{at}brown.edu.
H2O2 stimulates gallbladder muscle contraction and scavengers of free radicals through the generation of PGE2. Oxidative stress causes lipid peroxidation and generation of platelet-activating factor (PAF) or PAF-like lipids. The present studies therefore were aimed at determining whether either one induced by H2O2 mediates the increased generation of PGE2. Dissociated muscle cells of guinea pig gallbladder were obtained by enzymatic digestion. Both PAF-like lipids and PAF induced muscle contraction was blocked by the PAF receptor antagonist CV3988. This antagonist also blocked the increased PGE2 production caused by PAF-like lipids or PAF. The actions of PAF-like lipids were completely inhibited by indomethacin but those of PAF were only partially reduced by indomethacin or by NDGA and completely blocked by their combination. PAF-like lipids induced
contraction was inhibited by AACOCF3 (cPLA2 inhibitor) whereas the actions of
PAF were blocked by MJ33) (sPLA2 inhibitor). Receptor protection studies showed that pretreatment with PAF-like lipids prior to NEM protected the contraction induced by a second dose of PAF-like lipids or PGE2 but not by PAF. In contrast, pretreatment with PAF protected the actions of PAF and PGE2 but not that of PAF-like lipids. Both PAF-like lipids and PAF induced contraction were inhibited by anti-G
q/11 antibody and by inhibitors of MAPK (Mitogen-activated protein kinase) and PKC (protein kinase C). In conclusion, PAF-like lipids seem to activate a pathway different from that of PAF probably by stimulating a different PAF receptor subtype.
