Isolation of rat hepatocyte plasma membranes. I. Presence of the three major domains.

Abstract
A rat liver plasma membrane [PM] preparation was isolated and characterized both biochemically and morphologically. The isolation procedure was rapid, simple and effective in producing a membrane fraction with the following biochemical characteristics: .apprx. 40-fold enrichment in 3 PM markers, 5''-nucleotidase, alkaline phosphodiesterase 1 (both putative bile canalicular membrane enzymes) and the asialoglycoprotein (ASGP) receptor (a membrane glycoprotein present along the sinusoidal front of hepatocyte); a yield of each of these PM markers that averaged .apprx. 16%; and minimal contamination by lysosomes, nuclei and mitochondria, but persistent contamination by elements of the endoplasmic reticulum. Morphological analysis of the preparation revealed that all 3 major domains of the hepatocyte plasma membrane (sinusoidal, lateral and bile canalicular) were present in substantial amounts. The identification of sinusoidal membrane was further confirmed when ASGP binding sites were localized predominantly to this membrane in the isolated PM using EM autoradiography. By morphometry, the sinusoidal front membrane accounted for 47% of the total membrane in the preparation, whereas the lateral surface and bile canalicular membrane accounted for 6.8 and 23%, respectively. This is the 1st report of such a large fraction of sinusoidal membrane in a liver plasma membrane preparation.