AJP - Gastrointestinal and Liver Physiology, Vol 252, Issue 3 398-G403, Copyright © 1987 by American Physiological Society
Intraluminal calcium modulates lipid dynamics of rat intestinal brush-border membranes
P. K. Dudeja, T. A. Brasitus, R. Dahiya, M. D. Brown, D. Thomas and K. Lau
The present investigations were performed to evaluate whether calcium
modulates the physical state and lipid composition of rat enterocyte plasma
membranes in vivo. Ca2+ [CaCl2 (50 mM) in NaCl] or NaCl (vehicle control)
was administered to rats by intraluminal (gavage) or intraperitoneal
routes. Sixty minutes later, brush-border (BBM) and basolateral membranes
(BLM) were prepared from the proximal small intestine. By use of the
fluorophores, DL-2-(9-anthroyl)-stearic acid (2-AS),
DL-12-(9-anthroyl)-stearic acid (12-AS), and 1,6-diphenyl-1,3,5-hexatriene
(DPH), steady-state fluorescence polarization studies demonstrated that
intraluminal calcium decreased the fluidity of BBM but not BLM compared
with their respective vehicle controls. These alterations in fluidity
could, at least in part, be attributed to the concomitant increase in
sphingomyelin content and the sphingomyelin/lecithin ratio (mol/mol)
observed in the BBM prepared from calcium-gavaged rats. To evaluate the
mechanism for these lipid alterations, enzyme activities involved in
sphingomyelin synthesis and degradation were measured and revealed an
increase in sphingomyelin synthase and a decrease in sphingomyelinase in
BBM prepared from calcium-gavaged rats. In contrast, intraperitoneal
administration of calcium failed to influence membrane fluidity, lipid
composition, or these enzymatic activities in either BBM or BLM.
