Demonstration of a high affinity receptor for 1,25-dihydroxyvitamin D3 in rat pancreas

The existence of a high affinity receptor for 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) in rat pancreas was biochemically demonstrated in this study. In order to study the properties of this putative receptor, we took advantage of the analysis of low ionic strength chromatin-localized 1,25(OH)2D3 receptor. Using this method, the susceptibility of receptor protein to enzymatic degradation was so decreased, and the contamination by plasma vitamin D binding protein (DBP) component was so efficiently eliminated that a specific, saturable binding for 1,25(OH)2D3 could be demonstrated in the saturation analysis and the peak for the receptor was consistently apparent in the sucrose density gradient analysis. The equilibrium dissociation constant (Scatchard Kd) was found to be 3.7 +/- 1.5 x 10(-10) (M), and the concentration of specific binding sites was calculated to be 1.22 +/- 0.40 (fmol/mg protein). The number of specific binding sites in the rat pancreas was only 0.44% of that present in rat intestine (277 +/- 19 (fmol/mg protein] and 6.7% of that in rat kidney (18.1 +/- 1.0 (fmol/mg]. However, when a correction is made for the 1,25(OH)2D3 receptor distribution in the tissues and expressed as the receptor concentration per receptor-containing cells, the rat pancreatic receptor level was calculated to be about 30% of the rat intestine. Sucrose density gradient sedimentation of this receptor yielded a value of 3.2 +/- 0.1 (S) for the sedimentation coefficient and this peak was displaceable by a 100-fold excess of nonradioactive 1,25(OH)2D3.(ABSTRACT TRUNCATED AT 250 WORDS)