G-ALPHA(14) AND G-ALPHA(Q) MEDIATE THE RESPONSE TO TRYPSIN IN XENOPUSOOCYTES

Xenopus oocytes respond to trypsin with a characteristic chloride curr ent, virtually indistinguishable from responses mediated by a large nu mber of native and expressed G protein-coupled receptors. We studied t he involvement of G proteins of the G alpha(q) family as possible medi ators of this and other G protein-coupled receptor-mediated responses in Xenopus oocytes. We have cloned the third member of the G alpha(q) family, Xenopus G alpha(14), in addition to the previously cloned Xeno pus G alpha(q) and Ga,, (Shapira, H., Way, J., Lipinsky, D., Oron, Y., and Battey, J. F. (1994) FEES Lett. 348, 89-92). Amphibian G alpha(14 ) is 354 amino acids long and is 93% identical to its mammalian counte rpart. Based on the G alpha(14) cDNA sequence, we designed a specific antisense DNA oligonucleotide (antiG alpha(14)) that, together with an tiG alpha(q) and antiG alpha(11), was used in antisense depletion expe riments. 24 h after injection into oocytes, either antiG alpha(q) or a ntiG alpha(14) reduced the response to 1 mu g/ml trypsin by 70%, where as antiG alpha(11) had no effect. A mixture of antiG alpha(q) and anti G alpha(14) virtually abolished the response. These data strongly sugg est that G alpha(q) and G alpha(14) are the exclusive mediators of the trypsin-evoked response in Xenopus oocytes. Similar experiments with the expressed gastrin-releasing peptide receptor and muscarinic mi rec eptor revealed the coupling of G alpha(q) and G alpha(11) but not G al pha(14) to these receptors in oocytes. These results confirm the hypot hesis that endogenous members of the Gag family discriminate among dif ferent native receptors in vivo.