G-ALPHA-11 AND G-ALPHA-Q GUANININE NUCLEOTIDE REGULATORY PROTEINS DIFFERENTIALLY MODULATE THE RESPONSE TO THYROTROPIN-RELEASING-HORMONE IN XENOPUS OOCYTES

Xenopus oocytes that express mouse thyrotropin-releasing hormone receptors (TRH-Rs) after injection if RNA transcribed from TRH-R cDNA respond to THR by a depolarizing current. This response is transduced by activation of phosphoinositide-specific phospholipase C and utilizes an as yet unidentified endogenous guanine nucleotide-binding regulatory (G) protein(s). The alpha-subunit of G11 and G(q) have recently been shown to couple receptors to activation of phospholipase C. To determine whether there are functional differences between these proteins, we have co-expressed the TRH-R with either alpha-11, or alpha(q). Alpha-11 potentiated the response to TRH (by 61+/-16%), while alpha(q), inhibited the response (by 37+/-9%). The changes in amplitudes were accompanied by inverse changes in response latencies. These data show that alpha-11 and alpha(q) differentially modulate signal transduction in Xenopus oocytes.