Immunochemical studies on the putative plasmalemmal receptor for 1, 25-dihydroxyvitamin D(3). III. Vitamin D status

The effect of vitamin D status on levels of the putative 1, 25(OH)(2)D(3) membrane receptor (pmVDR) was studied in chick intestine, kidney, and brain. Western analyses and assays for specific [(3)H]1,25(OH)(2)D(3) binding indicated that, in intestine, pmVDR levels were greatest in -D chicks relative to +1,25D and +D animals (P < 0.05). In kidney, protein levels and specific binding followed the order +D > +1,25D, -D. In brain, vitamin D status did not affect protein levels or specific binding levels. In tissue from normal chicks, both protein and specific binding followed the order of intestine > kidney > brain membranes. Intestinal cells were further evaluated for the effect of 1,25(OH)(2)D(3) on selected "rapid responses." Extrusion of (45)Ca in response to 130 pM 1, 25(OH)(2)D(3) in vitro was greater in cells from -D chicks than from +1,25D or normal birds. Analyses of signal transduction events revealed diminished hormone-induced intracellular calcium oscillations (as assessed by fura-2 fluorescence), and lack of steroid-enhanced protein kinase (PK) A activity in intestinal epithelial cells from -D chicks relative to +D chicks. PK C activation by 130 pM 1,25(OH)(2)D(3) was approximately twofold in cells from +D or -D chicks. The combined results indicate that vitamin D status differentially affects the pmVDR in intestine, kidney, and brain. In intestine, vitamin D deficiency differentially affects (45)Ca handling, intracellular calcium oscillations, PK A and PK C activities in response to 1,25(OH)(2)D(3).