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Specificity of TRH receptor coupling to G‐proteins for regulation of ERG K + channels in GH 3 rat anterior pituitary cells
Author(s) -
Miranda Pablo,
Giráldez Teresa,
De La Peña Pilar,
Manso Diego G.,
AlonsoRon Carlos,
GómezVarela David,
Domínguez Pedro,
Barros Francisco
Publication year - 2005
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2005.085803
Subject(s) - thyrotropin releasing hormone , medicine , endocrinology , receptor , erg , g protein , biology , gq alpha subunit , anterior pituitary , hormone , chemistry , biochemistry , retinal
The identity of the G‐protein coupling thyrotropin‐releasing hormone (TRH) receptors to rat ether‐à‐go‐go related gene (r‐ERG) K + channel modulation was studied in situ using perforated‐patch clamped adenohypophysial GH 3 cells and dominant‐negative variants (Gα‐QL/DN) of G‐protein α subunits. Expression of dominant‐negative Gα q/11 that minimizes the TRH‐induced Ca 2+ signal had no effect on r‐ERG current inhibition elicited by the hormone. In contrast, the introduction of dominant‐negative variants of Gα 13 and the small G‐protein Rho caused a significant loss of the inhibitory effect of TRH on r‐ERG. A strong reduction of this TRH effect was also obtained in cells expressing either dominant‐negative Gα s or transducin α subunits, an agent known to sequester free G‐protein βγ dimers. As a further indication of specificity of the dominant‐negative effects, only the dominant‐negative variants of Gα 13 and Rho (but not Gα s ‐QL/DN or Gα t ) were able to reduce the TRH‐induced shifts of human ERG (HERG) activation voltage dependence in HEK293 cells permanently expressing HERG channels and TRH receptors. Our results demonstrate that whereas the TRH receptor uses a G q/11 protein for transducing the Ca 2+ signal during the initial response to TRH, this G‐protein is not involved in the TRH‐induced inhibition of endogenous r‐ERG currents in pituitary cells. They also identify G s (or a G s ‐like protein) and G 13 as important contributors to the hormonal effect in these cells and suggest that βγ dimers released from these proteins may participate in modulation of ERG currents triggered by TRH.