Rapid responses to thyroxine in the testis: Active protein synthesis-independent pathway

Abstract

We investigated the involvement of protein synthesis in the stimulatory action of thyroid hormones on amino acid accumulation and characterized K + currents involved in the hyperpolarizing effect of thyroxine ( T 4) on Sertoli cells. Immature rat testes were incubated in Krebs Ringer-bicarbonate buffer (KRb) in the presence of [ 14C]methylaminoisobutyric acid with and without T 4, 3,5,3′- l-triiodothyronine (T 3) and/or cycloheximide. Sertoli cells were monitored by intracellular recording in a chamber perfused with KRb with and without T 4, T 3 and/or blockers, and the membrane potential was monitored. T 4 and T 3 stimulated amino acid accumulation and protein synthesis. Treatment with cycloheximide diminished T 3 stimulatory actions on amino acid accumulation but had no effect on T 4 action. Both hormones elicited a hyperpolarization of the Sertoli cell membrane potential which involved K + channels, since TEA and apamin abolished this effect. These findings on rapid membrane actions of thyroid hormone in the testis suggest that some effects of T 4 are modulated by non-genomic mechanisms.