Gα₁₄ and Gα(q) mediate the response to trypsin in Xenopus oocytes

Xenopus oocytes respond to trypsin with a characteristic chloride current, virtually indistinguishable from responses mediated by a large number of native and expressed G protein-coupled receptors. We studied the involvement of G proteins of the Gα(q) family as possible mediators of this and other G protein-coupled receptor-mediated responses in Xenopus oocytes. We have cloned the third member of the Gα(q) family, Xenopus Gα₁₄, in addition to the previously cloned Xenopus Gα(q) and Gα₁₁ (Shapira, H., Way, J., Lipinsky, D., Oron, Y., and Battey, J. F. (1994) FEBS Lett. 348, 89- 92). Amphibian Gα₁₄ is 354 amino acids long and is 93% identical to its mammalian counterpart. Based on the Gα₁₄ cDNA sequence, we designed a specific antisense DNA oligonucleotide (antiGα₁₄) that, together with antiGα(q) and antiGα₁₁, was used in antisense depletion experiments. 24 h after injection into oocytes, either antiGα(q) or antiGα₁₄ reduced the response to 1 μg/ml trypsin by 70%, whereas antiGα₁₁ had no effect. A mixture of antiGα(q) and antiGα₁₄ virtually abolished the response. These data strongly suggest that Gα(q) and Gα₁₄ are the exclusive mediators of the trypsin-evoked response in Xenopus oocytes. Similar experiments with the expressed gastrin-releasing peptide receptor and muscarinic m1 receptor revealed the coupling of Gα(q) and Gα₁₁, but not Gα₁₄, to these receptors in oocytes. These results confirm the hypothesis that endogenous members of the Gα(q) family discriminate among different native receptors in vivo.