P2Y1 receptor modulation of endogenous ion channel function in Xenopus oocytes: Involvement of transmembrane domains

Agonist activation of the hP2Y1 receptor expressed in Xenopus oocytes stimulated an endogenous voltage-gated ion channel, previously identified as the transient inward (Tin) channel. When human P2Y1 (hP2Y1) and skate P2Y (sP2Y) receptors were expressed in Xenopus oocytes, time-to-peak values (a measure of the response to membrane hyperpolarization) of the Tin channel were significantly reduced compared to oocytes expressing the hB1-bradykinin receptor or the rat M1-muscarinic (rM1) receptor. Differences in activation were also observed in the Tin currents elicited by various P2Y receptor subtypes. The time-to-peak values of the Tin channel in oocytes expressing the hP2Y4, hP2Y11, or hB1-bradykinin receptors were similar, whereas the channel had significantly shorter time-to-peak values in oocytes expressing either the hP2Y1 or sP2Y receptor. Amino acid substitutions at His-132, located in the third transmembrane domain (TM3) of the hP2Y1 receptor, delayed the onset of channel opening, but not the kinetics of the activation process. In addition, Zn2+ sensitivity was also dependent on the subtype of P2Y receptor expressed. Replacement of His-132 in the hP2Y1 receptor with either Ala or Phe increased Zn2+ sensitivity of the Tin current. In contrast, truncation of the C-terminal region of the hP2Y1 receptor had no affect on activation or Zn2+ sensitivity of the Tin channel. These results suggested that TM3 in the hP2Y1 receptor was involved in modulating ion channel function and blocker pharmacology of the Tin channel

Observation of multiple hard photon final states at root s=130-140 GeV at LEP

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