Channel-mediated water movement across enclosed or perfused mouse intrahepatic bile duct units

We previously reported the developmentof reproducible techniques for isolating and perfusing intactintrahepatic bile duct units (IBDUs) from rats. Given the advantages oftransgenic and knockout mice for exploring ductal bile formation, wereport here the adaptation of those techniques to mice and theirinitial application to the study of water transport across mouseintrahepatic biliary epithelia. IBDUs were isolated from livers ofnormal mice by microdissection combined with enzymatic digestion. Afterculture, isolated IBDUs sealed to form intact, polarized compartments,and a microperfusion system employing those isolated IBDUs developed. Aquantitative image analysis technique was used to observe a rapidincrease of luminal area when sealed IBDUs were exposed to a series of inward osmotic gradients reflecting net water secretion; the choleretic agonists secretin and forskolin also induced water secretion into IBDUs. The increase of IBDU luminal area induced by inward osmotic gradients and choleretic agonists was reversibly inhibited by HgCl₂, a water channel inhibitor. With the use of aquantitative epifluorescence technique in perfused mouse IBDUs, a highosmotic water permeability (P_f = 2.5-5.6 × 10² cm/s) was found in response toosmotic gradients, further supporting the presence of water channels.These findings suggest that, as in the rat, water transport acrossintrahepatic biliary epithelia in mice is water channel mediated.