Integrin participates in the effect of thyroxine on plasma membrane in immature rat testis

Background: The secretory activity of Sertoli cells (SC) is dependent on ion channel functions and protein synthesis and is critical to ongoing spermatogenesis. The aim of this study was to investigate the mechanism of action associated with a non-metabolizable amino acid [C-14]-MeAIB (alpha-(methyl-amino)isobutyric acid) accumulation stimulated by T-4 and the role of the integrin receptor in this event, and also to clarify whether the T-4 effect on MeAIB accumulation and on Ca2+ influx culminates in cell secretion. Methods: We have studied the rapid and plasma membrane initiated effects of T-4 by using Ca-45(2+) uptake and [C-45]-MeAIB accumulation assays, respectively. Thymidine incorporation into DNA was used to monitor nuclear activity and quinacrine to analyze the secretory activity on SC. Results: The stimulation of MeAIB accumulation by T-4 appears to be mediated by the integrin receptor in the plasma membrane since tetrac and RGD peptide were able to nullify the effect of this hormone. In addition, T-4 increases extracellular Ca2+ uptake and Ca2+ from intracellular stocks to enhance nuclear activity, but this genomic action seems not to influence SC secretion mediated by T-4. Also, the cytoskeleton and CIC-3 chloride channel contribute to the membrane-associated responses of SC. Conclusions: T-4 integrin receptor activation ultimately determines the plasma membrane responses on amino acid transport in SC, but it is not involved in calcium influx, cell secretion or the nuclear effect of the hormone. General significance: The integrin receptor activation by T-4 may take a role in plasma membrane processes involved in the male reproductive system. (C) 2013 Elsevier BM. All rights reserved.