CHARACTERIZATION AND QUANTIFICATION OF RAT BILE PHOSPHATIDYLCHOLINE BY ELECTROSPRAY-TANDEM MASS-SPECTROMETRY

Rat bile phosphatidylcholine was structurally characterized and quanti fied by electrospray mass spectrometry using a triple quadrupole instr ument. All results were obtained by direct analysis of an unprocessed total lipid extract from rat bile. Structural characterization of phos phatidylcholine was achieved by collision-induced dissociation of [M Cl](-) ions observed in the negative-ion electrospray mass spectrum. Quantification of phosphatidylcholine was performed in the positive-io n mode using precursor ion scanning of m/z 184 and dimyristoylphosphat idylcholine as internal standard. Using this new methodology, the effe ct of cyclosporin A on biliary phosphatidylcholine excretion in the ra t was investigated. After intravenous administration of cyclosporin A (25 mg/kg body wt) the phosphatidylcholine level in bile was reduced t o about 30% of the control level. This suggests an inhibition by cyclo sporin A of the translocation of phosphatidylcholine across the hepato cyte canalicular membrane which is mediated by the Mdr2 P-glycoprotein . (C) 1997 Academic Press.