Gallbladder Na+/H+ exchange activity is up-regulated prior to cholesterol crystal formation

• Published in: European journal of clinical investigation Vol. 35; no. 8; pp. 514 - 522
• Main Authors: Narins, S. C., Ramakrishnan, R., Park, E. H., Smith, P. R., Meyers, W. C., Abedin, M. Z.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01-08-2005; Blackwell; Blackwell Publishing Ltd
• Subjects: Absorption; Animals; Bile - metabolism; Bile Acids and Salts - analysis; Biological and medical sciences; Cells, Cultured; Cholecystolithiasis - metabolism; Cholesterol - administration & dosage; Cholesterol - metabolism; Crystallization; Cultured epithelial cells; Diet; Dogs; Epithelial Cells - metabolism; gallbladder; Gallbladder - metabolism; gallstones; Gastroenterology. Liver. Pancreas. Abdomen; General aspects; Liver. Biliary tract. Portal circulation. Exocrine pancreas; Male; Medical sciences; Other diseases. Semiology; Phospholipids - analysis; Protein Isoforms; RNA, Messenger - analysis; Sodium - pharmacokinetics; sodium proton exchanger; Sodium-Hydrogen Exchangers - metabolism; Up-Regulation - physiology; Cell culture; sodium proton exchanger; gallstones; Crystals; Biliary tract disease; Cholelithiasis; Biological activity; Cholesterol; Exchange; Medicine; Regulation(control); Sodium; Proton; Digestive diseases; Epithelial cell; Gallbladder; Cultured epithelial cells; Formation
• ISSN: 0014-2972; 1365-2362
• DOI: 10.1111/j.1365-2362.2005.01520.x

Background  Gallbladder Na+ and H2O absorption are increased prior to gallstone formation and may promote cholesterol nucleation. Na+/H+ exchange (NHE) isoforms NHE2 and NHE3 are involved in gallbladder Na+ transport in prairie dogs. We examined whether increased gallbladder Na+ absorption observed during early gallstone formation is the result of NHE up‐regulation.
Materials and methods  Native gallbladder and primary cultures of gallbladder epithelial cells (GBECs) harvested from prairie dogs fed nonlithogenic (CON) or 1·2% cholesterol diet for varying lengths of time to induce cholesterol‐saturated bile (PreCRYS), cholesterol crystals (CRYS), or gallstones (GS) were used. NHE activity was assessed by measuring dimethylamiloride‐inhibitable 22Na+ uptake under H+ gradient in primary GBECs. HOE‐694 was used to determine NHE2 and NHE3 contributions. NHE protein and mRNA expression were examined by Western and Northern blots, respectively.
Results  Gallbladder total NHE activity was 25·1 ± 1·3 nmol mg protein−1 min−1 in the control and increased during gallstone formation peaking at the PreCRYS stage (98·4 ± 3·9 nmol mg protein−1 min−1). There was a shift in NHE activity from NHE2 to NHE3 as the animals progressed from no stones through the PreCRYS and CRYS stages to gallstones. The increase in NHE activity was partly caused by an increased Vmax without any change in KNam. Both NHE2 and NHE3 protein increased moderately during the PreCRYS stage without increases in mRNA expression.
Conclusions  Increased gallbladder Na+ absorption observed prior to crystal formation is in part caused by an increase NHE activity which is not fully accounted for by an increase in NHE proteins and mRNA levels but may be explained by enhanced localization in the membranes and/or altered regulation of NHE.