PTH-SENSITIVE K+- AND VOLTAGE-DEPENDENT P(I) TRANSPORT BY CHICK RENAL BRUSH-BORDER MEMBRANES

Brush-border membrane vesicles (BBMV) from chick (Gallus gallus) kidneys were use to examine possible pathways of P(i) transport associated with P(i) secretion. Preloading with 6 mM P(i) trans-stimulated P-32(i), uptake in the absence of Na+, indicating facilitation. Inside-positive voltage (100 mM K+, out > in, +valinomycin) increased P(i) uptake from 161 +/- 4.4 to 241 +/- 16.1 pmol . mg protein-1 . 5 s-1 at pH 7.5 (in = out). Gradients characterized by extravesicular pH (pH(o)) of 5.5 vs. intravesicular pH (pH(i)) of 7.5, 100 mM K+ (out > in), without and with valinomycin, further increased uptake to 664 +/- 148.5 and 946 +/- 90.8 pmol . mg protein-1 . 5 s-1, respectively. Carbonyl cyanide m-chlorophenylhydrazone (CCCP) had no effect on the latter response, but with 100 mM K+ (in = out), valinomycin decreased the response more than one-half, implicating a H+ diffusion potential. Generation of this potential with pH(o) 5.5 vs. pH(i) 7.5 and CCCP did not drive concentrative P(i) uptake in absence of K+. Parathyroid hormone (PTH) treatment significantly increased this BBMV K+- and voltage-dependent P(i) uptake compared with the parathyroidectomized (PTX) condition. The values of maximal uptake rate (V(max)) in PTH vs. PTX BBMV were 5,330 and 1,976 pmol . mg protein-1 . 5 s-1, respectively. K+-dependent transport was inhibited by arsenate, phosphonoacetic acid, and vanadate. Together, the data indicate that this PTH-sensitive, voltage- and K+-dependent monovalent P(i) transporter could be the mechanism by which P(i) exists, cell-to-lumen, during renal tubular P(i) secretion.