Abstract
1. The effect of the microtubule-disruptive agent, nocodazole (methyl [5-(2-thienylcarbonyl)-1H-benzimidazol-2-yl] carbamate), on the water permeability response to vasopressin or the synthetic cyclic AMP analogue, 8-parachlorophenylthio-cyclic AMP (8-CPT-cAMP), has been investigated in isolated cortical collecting tubules from rabbit kidneys, perfused in vitro. 2. Pre-treatment with nocodazole, 1-4 micrograms ml-1, had no significant effect on basal water permeability, but inhibited the increase in hydraulic conductivity elicited by vasopressin, 50 microU ml-1, in a dose-dependent manner. Inhibition of the response to the hormone averaged 65 +/- 6% (n = 8, P less than 0.001) at a nocodazole concentration of 4 micrograms ml-1. 3. Nocodazole, 1-4 micrograms ml-1, had no effect on the increase in lumen-negative potential difference (PD) induced by the hormone. 4. Pre-treatment with nocodazole, 4 micrograms ml-1, inhibited the development of the water permeability response to 8-CPT-cAMP, 1.8 x 10(-5) M, by 45 +/- 7% (n = 7, P less than 0.001). 5. When collecting tubules were exposed to nocodazole, 4 micrograms ml-1, after the hydrosmotic response to vasopressin had been fully established, the drug had no inhibitory effect on the maintenance of a high water permeability. 6. The results are consistent with the view that cytoplasmic microtubules play a role in the initiation of the water permeability response to vasopressin in the mammalian cortical collecting tubule at a cellular site beyond the generation of cyclic AMP.