AJP - Gastrointestinal and Liver Physiology, Vol 253, Issue 3 411-G419, Copyright © 1987 by American Physiological Society
Tissue distribution and vitamin D dependence of IMCAL in the rat
S. Kowarski, L. A. Cowen, M. T. Takahashi and D. Schachter
Integral membrane calcium-binding protein (IMCAL) is a vitamin D-dependent
integral membrane protein that binds calcium with relatively high affinity
(J. Biol. Chem. 225: 10834-10840, 1980). Specific immunoassays for IMCAL
utilizing rabbit polyclonal and mouse monoclonal antibodies were developed
and applied to studies of its tissue distribution and regulation by vitamin
D3 and dietary calcium in the rat. The results indicate that vitamin
D-dependent, cross-reactive protein is present in small intestinal mucosa,
cecal mucosa, bone, kidney, brain, testis, heart, lung, spleen, and skin.
Rats maintained on a low- (0.02%) compared with & high- (2.0%) calcium
diet had significantly higher content of IMCAL in duodenal mucosa, cecal
mucosa, bone, kidney, brain, testis, and heart. Treatment of rats on the
high-calcium diet with 1,25-dihydroxyvitamin D3 increased the IMCAL content
of the duodenal mucosa, cecal mucosa, and kidney. The widespread tissue
distribution of vitamin D-dependent IMCAL, its close correlation in
intestinal mucosa with the calcium transport mechanism, and its occurrence
in isolated preparations of enterocyte plasma membranes (microvillus and
basolateral membranes) suggest that the protein is involved in the
regulation of calcium flux in a number of cell types.
