1-BETA,25(OH)2-VITAMIN D3 IS AN ANTAGONIST OF 1-ALPHA,25(OH)2-VITAMIN D3 STIMULATED TRANSCALTACHIA (THE RAPID HORMONAL-STIMULATION OF INTESTINAL CALCIUM-TRANSPORT)

The steroid hormone 1α,25-dihydroxyvitamin-D3 [1α,25(OH)2D3] stimulates biological responses via both genomic mechanisms and nongenomic mechanisms (opening of voltage-gated Ca2+ channels). We report here that 1β,25(OH)2-vitamin-D3 (a) is devoid of activity as an agonist for transcaltachia, (b) is a potent stereospecific antagonist of 1α,25(OH)2D3 stimulation of the nongenomic transcaltachia response and also (c) has less than 1% the ability of 1α,25(OH)2D3 to bind to the chick intestinal nuclear 1β,25(OH)2D3 receptor. We conclude that the membrane response element(s) which generates the nongenomic response of transcaltachia has a different ligand specificity than the classic nuclear 1α,25(OH)2D3 receptor. © 1992.