Effects of Ions on Adrenocorticotropin-Sensitive Adenylate Cyclase of Rat Adrenals 1

Abstract

Summary

The basal activity of adenylate cyclase in homogenates of normal rat adrenals increased with the concentration of Mg²⁺ (1.25–10 mM) in the medium. The response of the enzyme to adrenocorticotropin (2 × 10^-5 M synthetic β^1–24 ACTH) and NaF (10 mM) was also determined by the concentration of Mg²⁺ in the incubation mixture: ACTH was more effective than NaF at low Mg²⁺ levels (1.25 and 2.5 mM) and less effective at 10 mM Mg²⁺. Of the monovalent cations tested, Li⁺ was more potent than Na⁺ in inhibiting the response of adrenal adenylate cyclase to ACTH. These cation effects were generally greater when medium Mg²⁺ was lower. The lowest Li⁺ concentration found to inhibit ACTH action significantly was 25 mM. K⁺ did not enhance the effect of ACTH on adrenal adenylate cyclase at 5 or 25 mM and depressed it at 100 mM (Mg²⁺:2.5 mM).