Bile canalicular contraction is coincident with reorganization of pericanalicular filaments and co-localization of actin and myosin-II.
We examined the relationships between actin-myosin interaction and bile canalicular contraction using a new experimental model: cytoskeleton-enriched canalicular membranes (CCM). In CCM, the bile canaliculus compartment is isolated complete with membrane-attached pericanalicular actin filaments and the surrounding intermediate filament sheath. Immunofluorescence and immunoelectron microscopy showed that actin and myosin-II were distributed over pericanalicular microfilaments that insert into adherens (belt) junctions; intermediate filaments predominantly inserted into desmosomes. The addition of "contraction solution" (1 microM Ca2+, 1 mM ATP) resulted in closure of CCM lumens, which was interpreted as canalicular contraction. Contraction was also associated with shortening and/or twisting of canaliculi. Rearrangement of actin filaments and myosin-II with co-localization of actin and myosin was observed. Evidence is also provided for attachment of actin-myosin-II aggregates to intermediate filaments coincident with contraction, suggesting a key scaffold function for intermediate filaments of the canaliculus. Attention is drawn to the overall similarity of structure-function dynamics in hepatic apical membranes to those described in intestinal brush border membrane preparations. The results are consistent with dynamic actin-myosin interaction with co-localization of actin and myosin-II in filament clumps coincident with canalicular contraction.
Tsukada
N
N
Research Institute, Hospital for Sick Children, University of Toronto, Ontario, Canada.
Phillips
M J
MJ
D008841:Actin Cytoskeleton / Q000737:chemistry / Q000648:ultrastructure*; D000199:Actins / Q000032:analysis*; D000818:Animals; D001648:Bile Canaliculi / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D005260:Female; D007150:Immunohistochemistry; D007382:Intermediate Filaments / Q000737:chemistry / Q000648:ultrastructure*; D007633:Keratins / Q000032:analysis; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D009218:Myosins / Q000032:analysis*; D051381:Rats; D017208:Rats, Wistar
D000199:Actins; D007633:Keratins; D009218:Myosins