[³H]-Aldosterone Binding Sites (Type I Receptors) in the Lateral Wall of the Cochlea: Distribution Assessment by Quantitative Autoradiography

Abstract

Mineralocorticoids, such as aldosterone, are steroids that enhance Na⁺ retention and K⁺ excretion in ion-transporting epithelial tissues through regulation of Na, K-ATPase. Previous studies suggest that aldosterone may regulate labyrinthine ion transport through up-regulation of Na, K-ATPase sites, a process mediated by high-affinity aldosterone (type I) receptors. In the present study, information concerning density and distribution of aldosterone binding sites in cochlear lateral wall tissues was determined by quantitative autoradiography using [³H]-aldosterone and RU-28362, a glucocorti-coid agonist that blocks low affinity binding to glucocorticoid (type II) receptors. The results revealed that the distribution of aldosterone binding sites differs among the individual cochlear regions of the lateral wall. The highest level of binding was associated with the stria vascularis and epithelial cells of the spiral prominence. Elevated levels of binding were also observed in stromal cells of the spiral prominence, and to a lesser extent in the spiral ligament. The differential distribution of aldosterone binding sites in the lateral wall resembles the pattern of localization of Na, K-ATPase sites observed in previous studies and is compatible with the idea that mineralocorticoids play a role in the regulation of cochlear cation transport.

Key Words:

• mineralocorticoids
• Na
• K-ATPase
• stria vascularis
• spiral prominence
• ion-transport