Motility of bile canaliculi in the living animal: implications for bile flow.

Abstract

Abstract. Modem fluorescence microscopic techniqueswere used to image the bile canalicular, system in the intact rat liver, in vivo. By combining the use of sodium fluorescein secretion into bile, with digitally enhanced fluorescence microscopy and time-lapse video, it was possible to capture and record the canalicular motility events that accompany the secretion of bile in life. Active bile canalicular contractions were found predominantly in zone 1 (periportal) hepatocytes of the liver. The contractile movements were repetitive, forceful, and appeared unidirectional moving bile in a direction towards the portal bile ducts. Contractions were not seen in the network of canaliculi on the surface of the liver. Cytochalasin B administration resulted in reduced canalicular motility, progressive dilation of zone 1 canaliculi, and impairment of bile flow. Canalicular dilations invariably involved the branch points of the canalicular network. The findings add substantively to previous in vitro studies using couplets, and suggest that canalicular contractions contribute physiologically to bile flow in the liver.TIN, myosin and associated proteins involved in contractile movements have been found in smooth muscle and nonmuscle cells (1,16,18,24,42,43,56,61,65). The majority of motility studies have been in vitro because this allows careful analysis of movements and of factors that influence them (23,26,27,43,46,59,64,68). It has been difficult to study the fine details of cell motility in vivo because oftechnicallimitations in resolution, but the marriage of computer-based, digital image processing with conventional microscopy achieves significant improvements in resolution, contrast, and visibility of fine detail. Most reports using these techniques used single cells or flattened cells or their processes (2,3,4,26,27,38). Here we report on the use of fluorescence imaging to demonstrate bile canalicular contractions in the substance of the liver, in the living state.Bile canaliculi are small channels formed by modifications of the plasma membranes of adjacent hepatocytes. Under normal conditions they are not visualized by conventional light microscopy. It is into these fine canals that bile is secreted by the liver cells. It has been generally considered that these are rigid channels that lack motility and that function as mere conduits conveying bile to the portal bile ducts. However, the bile canaliculi are surrounded by a rich investment of actin filaments (20,21,28,29,33,34,39,40,50,53). Using isolated hepatocyte couplets and time lapse microscopy, it has been shown that bile canaliculi repeatedly open and close and that this motion is accompanied by the expelling of a bolus of bile (52, 55). We have interpreted this motility as active bile canalicular contractions (47,52,54,55,66), but others consider the motile events as noncontractile collapses of canaliculi resulting from secretory pressure with rupture of canaliculi (9, 11,30,35). In this report, we have taken advantage of the biliary secretion of sodium fluores...

Quantitative intravital microscopy of hepatic transport

“…[34][35][36][37][38][39][40][41][42] As outlined below, we have adapted and extended the approaches used in these studies into quantitative assays of hepatocyte transport.…”

Efficient In Vitro vectorial transport of a fluorescent conjugated bile acid analogue by polarized hepatic hybrid WIF-B and WIF-B9 cells

“…2E-G), similar to those formed by hepatocytes after several days in primary cultures 27,28 and to the in vivo canalicular structures. 24 Lateral and basolateral markers such as cadherins, HA 321 and CE9, 22 were excluded from membrane of WIF 12-6 tubular and round BC, whereas other apical proteins, such as dipeptidyl peptidase IV and 5Ј-nucleotidase 14,22 and the tight junction-associated protein 578 BRAVO, BENDER, AND CASSIO ZO-1 were found concentrated in these structures or lining them, respectively (results not shown). In view of their hepatic polarized phenotype, the capacity of these four clones to transport CGamF was examined.…”

“…14 These canalicular spaces had a spherical shape, quite different from the network that bile canaliculi form in vivo, 24 but they were similar to the round spaces that appeared between hepatocyte doublets in vitro. 25,26 Remarkably, in dense cultures of the cell line WIF 12-6, we could also observe in addition to spherical spaces, tube-like intercellular spaces ( Fig.…”

Clinical Pathology Approaches to Hepatic Injury

“…These normally obstruct movement of substances between the bile and blood. Pulsatile contractions of the bile canaliculi help to propel the bile through the biliary tree and ultimately into the duodenum through the sphincter of Oddi (Watanabe et al, 1991). Decreased bile flow, i.e., cholestasis, results in increased concentrations of biliary constituents in the blood.…”