Clarification of the intercellular space phenomenon in toad urinary bladder.

Vasopressin has been noted to increase the size of the intercellular spaces of toad bladder epithelium even in the absence of an osmotic gradient. The present studies demonstrate that the same phenomenon may be obtained in the presence or absence of a transepithelial gradient of glutaraldehyde indicating that the effect is not a fixation artifact. Morphologic evidence is presented demonstrating continuity between the epithelium and underlying smooth muscle. The data support the concept that not only net water flow, but also changes in smooth muscle tone can appreciably affect the epithelial geometry.