Plasma membrane modulation of ampullar dark cells by corticosteroids.

Individual effects of corticosteroids on the ultrastructure of rat ampullar dark cells were quantitatively determined. Adrenalectomized rats subsequently received either aldosterone or dexamethasone or only hormone solvent via miniosmotic pumps for a period of 14 days. Ampullar tissues of the animals were processed for transmission electron microscopy, and standardized regions of ampullar dark cells were photographed and morphometrically analyzed. Surface density and boundary length of basolateral membrane increased significantly after hormone substitution with aldosterone, but not after replacement with dexamethasone, as compared with animals that received only solvent. No significant differences were observed for other morphological parameters between the groups. This response of ampullar dark cells to aldosterone appears similar to that of principal cells of the collecting duct in comparable experimental conditions. These morphological observations suggest that the mineralocorticoid, aldosterone, modulates ampullar dark-cell membranes.