Crawford J M, Möckel G M, Crawford A R, Hagen S J, Hatch V C, Barnes S, Godleski J J, Carey M C
Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
J Lipid Res. 1995 Oct;36(10):2147-63.
Physical-chemical and biological studies of hepatic bile suggest that biliary phospholipid molecules are secreted as unilamellar vesicles. Systematic ultrastructural studies of bile canaliculi were undertaken to visualize this event. Liver tissue was obtained from normal adult male rats (control), from bile salt-depleted rats (by overnight biliary diversion), and from depleted rats infused intravenously with a hydrophilic-hydrophobic congener series of common taurine-conjugated bile salts. Livers were fixed in situ either by modified chemical methods or by ultrarapid cryofixation. In control rats, chemical fixation revealed unilamellar vesicles 63 +/- 17 (+/- SD) nm in diameter, mostly free within canalicular lumena. Vesicles were infrequent in canaliculi of bile salt-depleted rats, but were present in canaliculi of rats infused with taurocholate. In cryofixed liver tissue, vesicles 67 +/- 13 nm in diameter were observed in canaliculi of control rats and bile-salt depleted rats infused with common bile salts. The majority of these vesicles were affixed to the luminal side of the canalicular membrane. The average number of vesicles per bile canaliculus was in agreement with that estimated on the basis of biliary phospholipid secretion rates, mean vesicle size, and area of close-packed phosphatidylcholine molecules. By immunoelectron microscopy, canalicular vesicles were free of actin and of a 100 kDa canalicular membrane protein. We conclude that biliary phospholipid molecules are secreted from hepatocytes into bile canalicular lumena as unilamellar vesicles approximately 63-67 nm in average diameter. We postulate that this secretion mechanism involves lumenal bile salt-induced vesiculation of lipid microdomains in the exoplasmic hemileaflet of the canalicular membrane.
肝胆汁的物理化学和生物学研究表明，胆汁磷脂分子以单层囊泡的形式分泌。我们对胆小管进行了系统的超微结构研究，以观察这一过程。从正常成年雄性大鼠（对照组）、胆盐缺乏大鼠（通过过夜胆汁引流）以及静脉注射一系列亲水-疏水共轭的常见牛磺酸结合胆盐的缺乏大鼠获取肝脏组织。肝脏通过改良化学方法或超快速冷冻固定原位固定。在对照大鼠中，化学固定显示直径为63±17（±标准差）nm的单层囊泡，大多游离于胆小管腔中。胆盐缺乏大鼠的胆小管中囊泡较少，但在注射牛磺胆酸盐的大鼠的胆小管中存在囊泡。在冷冻固定的肝脏组织中，在对照大鼠和注射常见胆盐的胆盐缺乏大鼠的胆小管中观察到直径为67±13 nm的囊泡。这些囊泡大多附着于胆小管膜的腔面。每个胆小管的囊泡平均数量与根据胆汁磷脂分泌率、平均囊泡大小以及紧密堆积的磷脂酰胆碱分子面积估算的数量一致。通过免疫电子显微镜观察，胆小管囊泡不含肌动蛋白和一种100 kDa的胆小管膜蛋白。我们得出结论，胆汁磷脂分子以平均直径约63 - 67 nm的单层囊泡形式从肝细胞分泌到胆小管腔中。我们推测这种分泌机制涉及管腔胆盐诱导胆小管膜外质半层脂质微区形成囊泡化。
