|Budget Amount *help
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 1995: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1994: ¥1,400,000 (Direct Cost: ¥1,400,000)
This study was undertaken to investigate the role of phospholipid species which had different head groups and hydrophobicity in the transcytotic vesicle fusion to canalicular membrane inner leaflet by using rat canalicular membrane vesicles (CMV) and liposomes. CMV were purified from the livers of Sprague-Dawley rats, and small unilamellar vesicles (SUV) of phosphatidylserine (PC) , phosphatidylcholine (PC) and mixture of PS/PC (1 : 1,2 : 1 and 4 : 1) were labeled with 8 mol% of octadecyl rhodamine B chloride (R18). PC species used in this study were egg yolk PC (EYPC) , soybean PC (SBPC) , dipalmitoyl PC (DPPC) and dilinoleoyl PC (DLPC). Fusion of SUV to CMV was initiated by the addition of millimolar concentration of Ca^<2+>, and the degree of fusibility was estimated by the increase of R18 fluorescence. Ca^<2+> dependent fusion of SUVs consisting of PS and PS/PC (4 : 1) to CMV was observed ; PS>PS/PC (4 : 1) , whereas no detectable fusion was evident between CMV and SUV of PC alone PS/PC (1 : 1 or 2 : 1). The ranking order of fusibility between CMV and SUV of PS/PC (4 : 1) of various PC species was PS/DLPC>PS/SBPC>PS/EYPC>PS/DPPC.Also hydrophobic index of PC determined by HPLC was closely related to fusibility (r=-0.96). These results suggest that transcytotic vesicles fuse to canalicular membrane inner leaflet by Ca^<2+> dependent procedure, and that its fusibility is regulated by phospholipid hydrophobicity of vesicles.