Biliary lipids alter ion transport during cholesterol gallstone formation

Abstract

Recent studies indicate that gallbladder absorption increases during the early stages of experimentally induced cholesterol gallstone formation. The purpose of the present study was to ascertain whether this change results from an alteration in gallbladder mucosal function per se or is a response of an otherwise healthy mucosa to the presence of cholelithogenic bile. Prairie dogs were fed either a control chow or a 1.2% cholesterol-enriched chow for 9 (Pre-GS) or 21 (Chronic-GS) days. Gallbladders were mounted in an Ussing-type chamber and electrophysiologic indices of ion transport were determined. Mucosal function was assessed independently by exposing the gallbladder to Ringer's solution in the absence of biliary lipids. Ion transport was similar in control and Pre-GS gallbladders but was significantly reduced in Chronic-GS animals. Gallbladders were subsequently exposed to model bile solutions containing bile acids and phospholipids in concentrations selected so as to reflect the relative concentration of bile salts and phospholipids in normal and cholesterol gallstone animals. The cross-comparison of control gallbladders exposed to nonlithogenic bile with Pre-GS gallbladders exposed to model cholelithogenic bile, therefore, simulates the in vivo situation and directly assesses the role of biliary lipids as a determinant of ion transport. When this comparison was performed there was a significant increase in short-circuit current ( P < 0.05) and potential difference ( P < 0.05) in Pre-GS animals as compared to controls. We propose that the increase in gallbladder absorptive function results from exposure of an otherwise healthy, functioning mucosa to cholelithogenic bile, and not from a change in mucosal function per se.