The classical
transient receptor potential channel 5 (TRPC5) is a molecular candidate for nonselective
cation channel (NSCC) activated by
muscarinic receptor stimulation whereas extracellular pH inhibits or enhances NSCC activated by
muscarinic receptor stimulation depending on extracellular
cation compositions in native tissues. We investigated the effect of extracellular pH on TRPC5 and determined
amino acid residues responsible for sensing extracellular pH. Extracellular
acidosis inhibits TRPC5 with pKa of 6.24. Under 50 mM intracellular
HEPES buffer condition, extracellular
acidosis inhibits TRPC5 with pKa of 5.40. We changed titratable
amino acids (C, D, E, H, K, R, Y) to nontitratable
amino acids (A, N, Q, N, N, N, F) within pore region between transmembrane segments 5 and 6 in order to determine the residues sensing extracellular pH.
Glutamate (at the position 543, 595, and 598),
aspartate (at the position 548) and
lysine (at the position 554) were responsible for sensing extracellular pH. The effect of extracellular pH in TRPC5 was also dependent on the composition of extracellular
monovalent cations. In conclusion, TRPC5 is a molecular candidate for NSCC activated by
muscarinic receptor stimulation, has
glutamate amino acid residues responsible for sensing extracellular pH, and has a unique gating property depending on the composition of extracellular
monovalent cations.