Microtubule assembly in renal medullary slices: effects of vasopressin, vinblastine, and lithium.

The effects of vasopressin and some of its inhibitors on the extent of MT polymerization (assembly) were studied in renal medullary slices by means of temperature-dependent polymerization-depolymerization procedure to determine the relative ratio of free (unpolymerized) tubulin to assembled MT's. Assembled MT's were stabilized in a medium containing high concentrations of glycerol and DMSO. Tubulin was assessed indirectly by the [3H]-CLC-binding assay. Incubation of slices at temperatures higher than 20 degree C promoted MT polymerization. Although vasopressin markedly increased the tissue levels of cAMP and activated in situ cAMP-dependent protein kinase, it did not change the extent of MT polymerization. On the other hand, VBL and to a lesser degree lithium chloride inhibited the rate of MT assembly. This finding suggests that VBL and lithium, which are known to inhibit the antidiuretic effect of vasopressin in vivo, may exert at least part of their inhibitory effect by interfering with MT assembly in the renal medulla. Present results thus are consistent with the view that vasopressin does not influence the extent of cytoplasmic MT polymerization in spite of the increase in tissue cAMP level and activation of protein kinase but that inact MT's are required for the cellular action of vasopressin.