Although the biological effects of thyroid hormones are mediated by nuclear receptors (genomic mechanisms), interactions with receptors associated with the plasma membrane (non-genomic mechanisms) of target cells are not clear. In this study we investigated the rapid stimulatory effect of thyroxine (T(4)) on (45)Ca(2+) uptake as well as ionic currents and intracellular messengers involved in the stimulatory action of T(4) in amino acid accumulation in immature rat testes. Results indicated that 10(-9)M or 10(-6)M T(4) was able to increase immediately (45)Ca(2+) uptake after 60s of hormone exposure. These results indicate for the first time that voltage-dependent Ca(2+) channels and ATP-dependent K(+) channels can be seen as a set-point in the stimulatory effect of T(4) on amino acid accumulation. Apamin-sensitive small-conductance Ca(2+)-activated K(+) channels (SK(Ca)) and chloride channels were shown to be partially involved in this mechanism. The amino acid accumulation triggered by the PKC pathway suggests a functional link between different ion channel activities and the stimulatory effect of T(4) on amino acid accumulation. In conclusion, we show in this study a rapid and stimulatory effect of T(4) on calcium uptake and on amino acid accumulation, both events initiated at the plasma membrane, which strongly characterizes a non-genomic effect of T(4) in immature rat testes.
Copyright 2010 Elsevier Ltd. All rights reserved.