Permselectivity of biliary canalicular membrane in rats: clearance probe analysis.

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Abstract
Biliary clearances of [3H]sucrose (CS) and [methoxy-3H]inulin (CH) were compared with those of similar metabolically inert, lipid insoluble, MW matched anions-sodium [14C]ferrocyanide (CF) and [carboxyl-14C]inulin (CC), respectively-during graded taurocholate choleresis in 31 anesthetized male rats as a means of assessing the permselectivity of the biliary canaliculi. All clearances were directly and significantly (P < 0.001) correlated with taurocholate excretion, CF was always less than CS measured simultaneously in 10 rats (CF/CS = 0.44 .+-. SE 0.03), and CC less than CH in 9 (CC/CH = 0.56 .+-. 0.10). The ratios were lower in the bile salt associated (BSA) (0.33 and 0.43) than in the bile salt independent (BSI) (0.54 and 0.58) fraction. The bioelectric barrier to anionic movement evident in the behavior of the 2 probe pairs appears to be more effective at the site of BSA than BSI fractional formation, independent of taurocholate excretion, and, on theoretical grounds, less effective in retarding ferrocyanide than carboxyl-insulin movement. Because control Cs and CH differed less than expected (0.218 .+-. 0.016 vs. 0.177 .+-. 0.012 .mu.l/min per g liver wt), sucrose and inulin may share to a considerable degree the same transmembrane pathways in which fixed charges or neutral polar sites are more closely approached by carboxyl-inulin than by ferrocyanide and which comprise some 10% of the area available to water movement.