Intracellular bile acid transport in rat liver as visualized by electron microscope autoradiography using a bile acid analogue
Suchy, F.J.; Balistreri, W.F.; Hung, J.; Miller, P.; Garfield, S.A.
American Journal of Physiology 245(5 Pt 1): G681-G689
1983
ISSN/ISBN: 0002-9513 PMID: 6638192 Document Number: 204122
The role of hepatocyte organelles in the intracellular transport and secretion of conjugated bile acids has not been defined. Therefore, the transport was studied and the subcellular localization of the bile acid analog 125I-cholylglycyltyrosine [125I-CGT] was observed by EM autoradiography to further understand the possible compartmentation of bile acids within the hepatocyte. 125I-CGT, which retains a net negative charge, exhibited transport properties similar to native bile acids. After portal vein injection, the compound was recovered intact from bile, and the pattern of excretion paralleled that of [14C]cholylglycine. In addition, CGT uptake by isolated hepatocytes was Na dependent. For autoradiography the analogue was injected into the portal vein, and the liver was perfusion fixed after 30 or 300 s. Light microscope autoradiography performed 30 s after isotope injection demonstrated a steep periportal-to-centrilobular gradient for 125I-CGT uptake. At 30 s, quantitative grain analysis of EM autoradiographs showed predominant labeling of the plasma membrane and the smooth endoplasmic reticulum (SER). The grain distribution over the region of the plasma membrane decreased from 15% at 30 s to 7% by 300 s and was associated with a 2-fold increase in labeling of the Golgi apparatus and a 6-fold increase in labeling of the pericanalicular region. Grain distribution over the SER at 30 s was the same as that noted at 30 s. The hypothesis is presented that bile acids move from the sinusoidal plasma membrane to bile via a pathway that includes the SER and Golgi apparatus.