Rat adrenal zona fasciculata cell electrophysiological responses to ACTH and gamma-MSH vary with age

Abstract

A comparison was made of the resting membrane potential (MP) as well as the MP responses to K+, ACTH and gamma-MSH of superfused adrenocortical, zona fasciculata cells from young (Y) and old (O) male rats. The resting MP of these cells did not vary with age. However, the MP responses to altered extracellular [K+] varied significantly with age. A prolonged biphasic depolarization was observed following ACTH administration; these responses were significantly reduced in O cells. In contrast, stimulation with gamma-MSH did not consistently elicit depolarization in the Y but caused a consistent and prominent depolarization in O cells. These findings suggest that aging is associated with changes in primary membrane events which could explain the reduced ACTH-stimulated steroidogenesis associated with age. Elevated cellular responses to gamma-MSH may contribute to a maintenance of, or increase in, circulating corticosterone levels in aged rats.