Patterns of membrane organization in toad bladder epithelium: a freeze-fracture study

Two cell-types of toad bladder epithelium show uncommon plasma membrane organization in freeze-fractured specimens. One type, the granular cell, contains a plasma membrane in which the A-face is poorly particulate luminally while the B-face discloses multiple large particles at this site. In contrast, the lateral and basal portions of the granular-cell membrane are typical in that more particles occupy the A-face than the B-face. In the other cell-type, which is mitochondria-rich, the plasma membrane, luminally, laterally, and basally, contains rod-shaped and a few globular particles in the A-face. We suggest that these two peculiar membrane organizations be considered in the localization of both vasopressin and aldosterone action in toad bladder.