Pre-steady-state analysis of the turn-on and turn-off of water permeability in the kidney collecting tubule.

Water transport across the mammalian collecting tubule is regulated by vasopressin-dependent water channel insertion into and retrieval from the cell apical membrane. The time course of osmotic water permeability (Pf) following addition and removal of vasopressin (VP) and 8-Br-cAMP was measured continuously by quantitative fluorescence microscopy using an impermeant fluorophore perfused in the lumen. Cortical collecting tubules were subjected to a 120 mOsm bath-to-lumen osmotic gradient at 37 degrees C with 10-15 nl/min lumen perfusion and 10-20 ml/min bath exchange rate. With addition of VP (250 microU/ml), there was a 23 +/- 3 sec (SEM, n = 16) lag in which Pf did not change, followed by a rise in Pf (initial rate 1.4 +/- 0.2 x 10(-4) cm/sec2) to a maximum of 265 +/- 10 x 10(-4) cm/sec. With addition of 8-Br-cAMP (0.01-1 mM) there was an 11 +/- 2 sec lag. For [8-Br-cAMP] = 0.01, 0.1 and 1 mM, the initial rate of Pf increase following the lag was (units 10(-4) cm/sec2): 1.1 +/- 0.1, 1.2 +/- 0.1 and 1.7 +/- 0.3. Maximum Pf was (units 10(-4) cm/sec): 64 +/- 4, 199 +/- 9 and 285 +/- 11. With removal of VP, Pf decreased to baseline (12 x 10(-4) cm/sec) with a T1/2 of 18 min; removal of 0.1 and 1 mM 8-Br-cAMP gave T1/2 of 4 and 8.5 min.(ABSTRACT TRUNCATED AT 250 WORDS)