A: Proton-gated ion channel B: Proton-gated ion channel C: Proton-gated ion channel D: Proton-gated ion channel E: Proton-gated ion channel F: Proton-gated ion channel G: Proton-gated ion channel H: Proton-gated ion channel I: Proton-gated ion channel J: Proton-gated ion channel K: Proton-gated ion channel L: Proton-gated ion channel M: Proton-gated ion channel N: Proton-gated ion channel O: Proton-gated ion channel P: Proton-gated ion channel Q: Proton-gated ion channel R: Proton-gated ion channel S: Proton-gated ion channel T: Proton-gated ion channel