Bile canalicular contraction and dilatation in primary culture of rat hepatocytes--possible involvement of two different types of plasma membrane Ca(2+)-Mg(2+)-ATPase and Ca(2+)-pump-ATPase.
Increasing evidence has indicated that bile canalicular contraction is mediated by the nonmuscular Ca(2+)-calmodulin-actomyosin system, and the contraction facilitates canalicular bile flow. The aim of the present study was to examine, by electron cytochemistry, how the expression of two types of plasma membrane Ca(2+)-ATPase, i.e., Ca(2+)-Mg(2+)-ATPase and Ca(2+)-pump-ATPase, is related to the dynamic changes of bile canalicular contraction. Hepatocytes isolated from male Wistar rat liver by collagenase perfusion were cultured to form a primary monolayer. The canalicular dynamics in the couplets and triplets were analyzed by time-lapse cinematography. The Ca(2+)-Mg(2+)-ATPase activity was identified by the electron cytochemical method of Ando. Ultrastructural localization of Ca(2+)-pump-ATPase was examined by immunogold electron microscopy. We found that cytochemical reaction products showing the presence of Ca(2+)-Mg(2+)-ATPase activity were localized on the luminal side of the bile canalicular membranes. Immunogold particles, indicating the presence of Ca(2+)-pump-ATPase, were located mainly on the cytoplasmic side of the bile canalicular membranes. The expression of both Ca(2+)-ATPases on the canalicular membranes was enhanced during the contracting stage of bile canaliculi, whereas their expression was diminished in the dilating stage. We conclude that two different types of bile canalicular Ca(2+)-ATPase may be involved in the regulation of canalicular contractility to control the extrusion of intracytoplasmic free calcium ions into the canalicular lumen.
Yokomori
H
H
Department of Internal Medicine, Kitasato Institute Medical Center Hospital, 121-1 Arai Kitamotoshi, Saitama 364-8501, Japan. yokomri-hr@kitasato.or.jp
Oda
M
M
Kamegaya
Y
Y
Ogi
M
M
Tsukada
N
N
Ishii
H
H
D000818:Animals; D001648:Bile Canaliculi / Q000201:enzymology / Q000502:physiology*; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology; D002478:Cells, Cultured; D006651:Histocytochemistry; D008099:Liver / Q000201:enzymology*; D008297:Male; D008854:Microscopy, Electron; D009119:Muscle Contraction; D009126:Muscle Relaxation; D051381:Rats; D017208:Rats, Wistar
D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases