Effect of vasopressin and serosal hypertonicity on toad urinary bladder

Effect of vasopressin and serosal hypertonicity on toad urinary bladder. The mucosal surface of toad urinary bladder was examined with scanning electron microscopy following its exposure to 20 mU/ml of vasopressin (VP), 10 −4 M 8-bromo-cAMP, 1mM acetylcholine chloride, serosal hypertonicity, or a hypotonic bathing medium. After a 30-min exposure to VP, the arborizing ridge-like surface pattern typical of granular cells was transformed into microvilli, a response that was not dependent on transepithelial osmotic water movement. An identical response occurred following a 30-min exposure of the bladder to 8-bromo-cAMP, again in the absence of an osmotic gradient. Microvillus formation was not observed when cell volume was increased by incubation of tissue in half-normal amphibian Ringer's solution for 30 min, or with exposure to acetylcholine, which caused accentuation of the convexity of the apical surface of the granular cell similar to that observed with VP-induced osmotic water flow. However, 60min of incubation in a hypertonic serosal medium (mannitol, 240mM) caused transformation of ridges to microvilli mimicking the picture obtained with VP. These findings establish that transepithelial osmotic water flow with cell swelling is not required for microvillus formation on the apical surface of granular cells following VP stimulation, and that the surface changes are not due to cell swelling alone or to changes in the configuration of the apical plasmalemma. The results also suggest that the response to VP is mediated via the generation of cAMP. Finally, this study demonstrates that serosal hypertonicity also causes transformation of ridges to microvilli by a mechanism that is yet to be defined. Effet de la vasopressine et de l'hypertonicite du cote sereux de la vessie urinarie de crapaud. La face muqueuse de la vessie urinaire de crapaud a ete etudiee en microscopie a balayage apres exposition a 20mU/ml de vasopressine (VP), a 10 −4 M de 8-bromo-cAMP, a 1mM de chlorure d'acetylcholine, a une hypertonicite sur la face sereuse ou a un milieu ambiant hypotonique. Apres 30min d'exposition a VP, l'aspect typique des cellules granulaires fait place a des microvillosites, et cette reponse ne depend pas du mouvement osmotique d'eau transepithelial. Une reponse identique est observee apres 30min d'exposition a 8-bromo-cAMP, la encore en l'absence de gradient osmotique. La formation de microvillosites n'a pas lieu quand le volume cellulaire est augmente par l'incubation du tissu dans du Ringer deminormal d'amphibien pendant 30min ou par l'exposition a l'acetylcholine qui determine l'augmentation de la convexite de la surface apicale de la cellule granuleuse, semblable a celle observee avec le debit osmotique d'eau produit par VP. Soixante minutes d'incubation avec du milieu sereux hypertonique (mannitol, 240mM) determine cependant la transformation en microvillosites et realise la meme image que VP. Ces constatations etablissent que le debit osmotique d'eau transepithelial avec gonflement cellulaire n'est pas necessaire a la formation de microvillosites sur la surface apicale des cellules granuleuses apres stimulation par VP et que les modifications de surface ne sont pas liees au gonflement cellulaire lui-meme ou a des modifications du plasmalemme apical. Les resultats suggerent aussi que la reponse a VP a pour mediateur la generation de cAMP. Enfin ces etudes demontrent que l'hypertonicite sereuse determine aussi l'apparition de microvillosites par un mecanisme qui reste a definir.