Proton modulation of M-like potassium current (IKx) in rod photoreceptors

The effect of extracellular pH (pH_e 6.9–8.1) and intracellular pH (pH_i 6.4–8.1) on the non-inactivating voltage-sensitive M-like potassium current (I_Kx) was studied in patch-clamped salamander rod photoreceptors. The midpoint of the I_Kx activation curve shifted by 6.6 mV per pH_e unit, with acidification producing positive shifts and alkalinization producing negative shifts. The time constant of I_Kx activation shifted with pH_e in a manner consistent with the shifts in the activation curve. Maximum conductance and gating charge were unaffected by changes in pH_e. I_Kx did not depend on pH_i. Given the importance of I_Kx in rod function, these results suggest that pH_e could affect the signal transmitted from rods by changing I_Kx activation parameters.