EFFECT OF COLCEMID ON THE WATER PERMEABILITY RESPONSE TO VASOPRESSIN IN ISOLATED PERFUSED RABBIT COLLECTING TUBULES

1. The effect of the microtubule-disruptive agent, colcemid (N-deacetyl-N-methyl-colchicine), on the water permeability response to vasopressin has been investigated in isolated cortical collecting tubules from the rabbit kidney perfused in vitro. 2. Pretreatment of collecting tubules with colcemid inhibited the increase in water permeability elicited by vasopressin, 50 muU ml-1, in a time- and dose-dependent manner. After 75 min exposure to the drug, inhibition of the response to the hormone averaged 72 +/- 6 % (n = 4, P < 0.01) at a colcemid concentration of 7.2 x 10(-5) M. Inhibition was estimated to be half-maximal at a colcemid concentration of 1.9 x 10(-6) M. 3. Colcemid, 2.7 x 10(-7) to 7.2 x 10(-5) M, had no effect on basal water permeability nor on the increase in lumen negative potential difference (PD) induced by the hormone. 4. Lumicolcemid, an isomer of colcemid that does not disrupt microtubules, had no influence on the water permeability response to vasopressin. 5. Pretreatment with colcemid, 2.7 x 10(-5) M, for 45 min inhibited the water permeability response to 8-CPT-cAMP, 1.8 x 10(-5) M, by 38 +/- 4% (n = 5, P < 0.01). 6. When collecting tubules were exposed to colcemid, 5.5 x 10(-5) M, for 45 min after the hydrosmotic response to vasopressin had been established, the drug had no influence on the maintenance of the raised water permeability. 7. The results provide further evidence that cytoplasmic microtubules play a role in the initiation of the hydrosmotic response to vasopressin in the mammalian collecting tubule at a site distal to the generation of cyclic AMP.