AJP - Gastrointestinal and Liver Physiology, Vol 262, Issue 6 990-G995, Copyright © 1992 by American Physiological Society
Convective movement of Ca2+ across guinea pig gallbladder epithelium
R. V. Rege and E. W. Moore
Department of Surgery, Northwestern University Medical School, Chicago, Illinois.
Recently, much interest has developed in biliary calcium because of its
importance in the pathogenesis and composition of gallstones. While much
progress has been made in understanding the thermodynamic factors that
control biliary calcium concentrations, little is known about the kinetic
factors that control the movement of calcium across the gallbladder
epithelium. These studies measure guinea pig gallbladder epithelial
permeability to Ca2+ during in vivo convective water movement across the
membrane. Water movement, ranging from -15.2 (absorption) to 6.3
microliters.min-1.cm-2 (water entry), was induced by placing hypotonic,
isotonic, and hypertonic solutions into the gallbladder lumen. Calcium
movement was found to be directly and linearly related to water flow,
indicating that Ca2+ moved with the convective water flow, presumably
across paracellular channels. The slope of this relationship (0.602),
representing the concentration of calcium in the fluid translocated across
the gallbladder epithelium, was only about half that of plasma or luminal
contents, indicating that calcium movement across the membrane was
restricted. The mean sieving coefficient (1 - r) of guinea pig gallbladder,
calculated from this slope, was approximately 0.5, indicating that the
epithelium is only moderately permeable to Ca2+. The results suggest that
intraluminal chelation of Ca2+ for the possible prevention and/or treatment
of calcium-containing gallstones is a potentially feasible therapeutic
modality.
