Specificity of TRH receptor coupling to G-proteins for regulation of ERG K+ channels in GH3 rat anterior pituitary cells.
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 (Galpha-QL/DN) of G-protein alpha subunits. Expression of dominant-negative Galpha(q/11) that minimizes the TRH-induced Ca2+ signal had no effect on r-ERG current inhibition elicited by the hormone. In contrast, the introduction of dominant-negative variants of Galpha13 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 Galpha(s) or transducin alpha subunits, an agent known to sequester free G-protein betagamma dimers. As a further indication of specificity of the dominant-negative effects, only the dominant-negative variants of Galpha13 and Rho (but not Galpha(s)-QL/DN or Galpha(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 Ca2+ 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 G13 as important contributors to the hormonal effect in these cells and suggest that betagamma dimers released from these proteins may participate in modulation of ERG currents triggered by TRH.
Miranda
Pablo
P
Departamento de Bioquímica y Biología Molecular, Edificio Santiago Gascón, Campus del Cristo, Universidad de Oviedo, E-33006, Oviedo, Asturias, Spain.
Giráldez
Teresa
T
de la Peña
Pilar
P
Manso
Diego G
DG
Alonso-Ron
Carlos
C
Gómez-Varela
David
D
Domínguez
Pedro
P
Barros
Francisco
F
D000818:Animals; D002460:Cell Line; D051638:Ether-A-Go-Go Potassium Channels; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D007668:Kidney / Q000378:metabolism*; D010902:Pituitary Gland / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D018025:Receptors, Thyrotropin-Releasing Hormone / Q000378:metabolism*
D051638:Ether-A-Go-Go Potassium Channels; D015221:Potassium Channels; D018025:Receptors, Thyrotropin-Releasing Hormone; D019204:GTP-Binding Proteins