Na+:H+ and Cl-:HCO3- exchange are localized, respectively, to basolateral (blLPM) and canalicular (cLPM) rat liver plasma membranes. To determine whether these exchangers play a role in bile formation, we examined the effect of a choleretic agent, ursodeoxycholate (UDCA), on these exchange mechanisms. 22Na (1 mM) and 36Cl (5 mM) uptake was determined using outwardly directed H+ and HCO3- gradients, respectively. Preincubation of blLPM vesicles with UDCA (0-500 microM) resulted in a concentration-dependent increase in initial rates of amiloride-sensitive pH-driven Na+ uptake, with a maximal effect at 200 microM. UDCA (200 microM) increased Vmax from 23 +/- 2 (control) to 37 +/- 7 nmol/min per mg protein; apparent Km for Na+ was unchanged. Preincubation with tauroursodeoxycholate (200 microM), taurocholate (10-200 microM) or cholate, chenodeoxycholate, or deoxycholate (200 microM) had no effect on pH-driven Na+ uptake. UDCA (200 microM) had no effect on either membrane lipid fluidity, assessed by steady-state fluorescence polarization using the probes 1,6-diphenyl-1,3,5-hexatriene, 12-(9-anthroyloxy) stearic acid, and 2-(9-anthroyloxy) stearic acid (2-AS), or Na+,K+-ATPase activity in blLPM vesicles. In cLPM vesicles, UDCA (0-500 microM) had no stimulatory effect on initial rates of HCO3(-)-driven Cl- uptake. Enhanced basolateral Na+:H+ exchange activity, leading to intracellular HCO3- concentrations above equilibrium, may account for the bicarbonate-rich choleresis after UDCA infusion.
R H Moseley, N Ballatori, D J Smith, J L Boyer
Usage data is cumulative from September 2021 through September 2022.
Usage information is collected from two different sources: this site (JCI) and Pubmed Central (PMC). JCI information (compiled daily) shows human readership based on methods we employ to screen out robotic usage. PMC information (aggregated monthly) is also similarly screened of robotic usage.
Various methods are used to distinguish robotic usage. For example, Google automatically scans articles to add to its search index and identifies itself as robotic; other services might not clearly identify themselves as robotic, or they are new or unknown as robotic. Because this activity can be misinterpreted as human readership, data may be re-processed periodically to reflect an improved understanding of robotic activity. Because of these factors, readers should consider usage information illustrative but subject to change.