A NOVEL TYPE OF MICROTUBULES IN THE FROG URINARY-BLADDER EPITHELIUM STIMULATED BY VASOPRESSIN

Changes in the cytoskeleton of granular cells of the frog urinary blad der under conditions of low and vasopressin-induced water permeability were investigated. Using a conventional electron microscopical prepar ation with glutaraldehyde/osmium fixation we found only the usual type of microtubules in granular cells of both resting and stimulated blad ders. These microtubules, 20 nm in diameter, were associated with cent rioles and Golgi complexes. Under the high water permeability conditio ns the large vacuoles appear in granular cells. The 20-nm microtubules and microfilaments were connected to the membrane of these vacuoles. The second type of 'thick' microtubules was found in granular cells of the stimulated bladder after the fixation with glutaraldehyde without osmium postfixation or freeze-substitution. The tubulin nature of the se 'thick' microtubules was identified immunocytochemically. In additi on, tubulin was present in the granules with crystalline content.