Vasopressin-induced Changes in the Toad Urinary Bladder Epithelial Surface

The ultrastructure of the epithelial cells of the toad urinary bladder . has been described by several laboratories (Choi, 1963 ; DiBona et al., 1969 a; Peachey and Rasmussen, 1961). This hormone-sensitive cell layer consists of four distinct cell types : (a) basal cells ; (b) goblet cells ; (c) granular cells ; and (d) mitochondria-rich cells . The granular cells are the most numerous, comprising 80-857 of the total . The mitochondria-rich cells represent 10-157 of the total, with the remainder represented by the other two types . All cells, except the basal cells, have direct access to the bladder lumen . Ultrastructural studies have also revealed changes in cell structure after the addition of the polypeptide hormone, arginine vasopressin (AVP), to the bathing medium . This hormone is known to increase transcellular sodium transport in this tissue and to increase its permeability to water as well as bulk water flow in the presence of a mucosal to serosal osmotic gradient (Leaf, 1967) . The effects of vasopressin on the epithelial cell layer have included the appearance of intracellular lakes during hormone-induced bulk H2O flow (Grantham et al ., 1971), cell swelling (Peachey and Rasmussen, 1961), intracellular granules migration, and increased glycocalyx deposition (Masur et al ., 1972), as well as the appearance of an increased number of small intracellular vesicles in both the granular and basal cells .' In spite of considerable speculation concerning the functional roles of the different cell types and particularly the possible relationship between the granular and mitochondria-rich cells, no specific evidence has heretofore been reported that links, no specific evidence has heretofore been reported that links these cell types in either an anatomical or functional relationship . Previous ultrastructural studies have employed standard transmission electron microscopy. The present report deals with studies of the ultrastructural architecture of the luminal (mucosal) surface of this tissue as determined by scanning electron microscopy . This investigation has revealed a repeating geometric arrangement of the surface architecture with units consisting of four or five flattened, polygonal cells surrounding a single smaller ovoid cell with distinctly different surface characteristics . In addition, scanning microscopy has revealed that the luminal processes on the granular cells, which appear as microvilli in transmission electron microscope sections, are in actuality a series of surface ridges . Finally, vasopressin, in addition to causing cell swelling, leads to a morphological alteration in these surface ridges .