Hormone-sensitive adenylate cyclase along the nephron of genetically hypophosphatemic mice

The response of the adenylate cyclase (AC) activity to PTH and calcitonin was measured along the nephron of normal (N) and mutant hypophosphatemic (Hyp) mice of the C 57 BL/6J strain, using in vitro single tubule AC microassay. In each experiment, a Hyp mouse was paired to a N mouse from the same litter. In the presence of PTH (10 U/ml), AC activities (femtomoles cAMP per millimeter of tubule per 30-min incubation) were reduced in the proximal convoluted tubule of Hyp mice as compared to N mice in all experiments (448 +/- (SEM) 46 vs. 831 +/- 79, N = 4, P less than 0.01). Some decrease in AC response to PTH also was noted in the cortical portion of the thick ascending limb of the loop of Henle (476 +/- 70 in Hyp mice vs. 719 +/- 83 in N mice, N = 4, P = NS). The Hyp and N AC responses to PTH were similar in the "bright" and "granular" portions of the distal convoluted tubule (1524 +/- 177 in Hyp mice and 1538 +/- 228 in N mice, N = 4). The other segments tested were not responsive to PTH (except the pars recta of the proximal tubule). In the presence of salmon calcitonin (10 ng/ml), a striking 5- to 12-fold increase in AC activity of the "bright" and "granular" portions of the distal convoluted tubule was observed in each Hyp mouse as compared to its paired N control (2434 +/- 618 vs. 399 +/- 56, N = 6, P less than 0.01). The AC response to calcitonin was also increased, though to a lesser extnet (Hyp/N = 1.8) in the "light" portion of the distal tubule (590 +/- 60 in Hyp and 352 +/- 36 in N mice, P less than 0.01). Other segments of the mouse nephron were also observed to contain calcitonin-sensitive AC, but the responses were of limited magnitude only and were not statistically different in Hyp and N mice. Dose-response curves showed that the decrease of the response to PTH in the proximal tubule as well as the increase of the response to calcitonin in the distal tubule were present in Hyp mice for the whole range of hormone concentrations tested. In both structures, the apparent Km for the cyclase activation by the hormone was similar in the Hyp and its paired N mouse.