G protein-activated K+ channels: a reporter for rapid activation of G proteins by lysophosphatidic acid in Xenopus oocytes.

Threshold concentrations of lysophosphatidic acid (LPA) or acetylcholine (ACh) induce pertussis toxin (PTX)-sensitive rapid desensitization of responses to LPA in Xenopus oocytes. To demonstrate that threshold [LPA] rapidly activates Gi/o proteins, we used the G protein-activated K+ channel (GIRK) as a reporter. Low [LPA] induced IK+ in <3 s of the agonist addition with little or no activation of chloride current. Depletion of Galphao/Galphao1 each decreased the LPA-induced IK+ by approximately 40-50%, while PTX completely abolished it. This is the first direct evidence showing the activation of GIRK by LPA, and the involvement of G proteins of the Go family in rapid desensitization of LPA responses.