EVIDENCE FOR 2 CLASSES OF 1,25-DIHYDROXYVITAMIN-D3 BINDING-SITES IN CLASSICAL VS NONCLASSICAL TARGET TISSUES

Possible differences in 1,25-Dihydroxyvitamin D3 [1,25(OH)2D3] binding sites in classical and nonclassical target tissues were tested by Scatchard analysis of [3H]1,25(OH)2D3 binding in parallel chromatin preparations of rat kidney vs. testis. Two distinct binding components were resolved in kidney (p<0.005). Moreover, the single binding site in testis exhibited a 10-fold lower Kd (p<0.05) than did the principal binding site in kidney (50±4 vs. 405±142 pM). Secondly, regulation of [3H]1,25(OH)2D3 binding sites also differed. 1,25(OH)2D3 injection resulted in increased 1,25(OH)2D3 binding (p<0.05) in kidney (92%) and intestine (415%),but not in testis, lung or heart. These results suggest that the principal 1,25(OH)2D3 binding sites in classical targets kidney and intestine may be intrinsically different from those in at least some nonclassical targets. © 1991 Academic Press, Inc.