Localization of receptors for 1,25-dihydroxyvitamin D3 along the rat nephron. Direct evidence for presence of the receptors in both proximal and distal nephron.

Abstract

We recently demonstrated that 25-hydroxyvitamin D3-24-hydroxylase, which can be further induced by 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), is localized exclusively in the proximal nephron of the vitamin Dreplete rat kidney.These data and the proposed mode of action of 1,25(OH)& predict the presence of a receptor for 1,25(OH)&3 in the proximal nephron.However, autoradiographic studies failed to detect significant nuclear uptake of 1,25(0H)~D3[~H]D~ in the proximal nephron.To localize and characterize receptors for 1,25-(OH)2D3 along the nephron, preparations of both microdissected defined nephron segments and isolated tubules from the whole kidney of vitamin D-deficient rats were incubated with 1,25(OH)2[3H]D3, and specific uptake of the sterol was assessed in the cytosol preparation of tubular cells sonicated in a hypertonic solution.The preparation of isolated tubules incubated for 1 h a t 37 "C accumulated 1,25(OH)2[3H]D3 with high affinity (Kd = 0.54 m), and the receptors exhibited a sedimentation constant of 3.7 S in a hypertonic sucrose gradient.The uptake of 1,25(OH)z[3H]D3 was also examined in three defined single nephron segments: proximal convoluted tubules, medullary thick ascending limb of Henle's loop, and collecting tubules.Both proximal convoluted tubules and medullary thick ascending limb of Henle's loop showed a significant uptake of 1,25-(OH)2[3H]D3, 29.9 f 8.1 and 20.8 f 4.5 fmol/lOOO-mm tubule length, respectively, while collecting tubules showed no significant uptake.The receptors in both segments sedimented at 3.7 S in sucrose gradient.These data demonstrate the presence of 1,%(OH)2D3 receptors in both proximal and distal nephron.The physiological actions of vitamin D are thought to be mediated by the hormonal metabolite, 1,25(OH)2D31 (1-3).