Outward K+ channels in Brassica chinensis pollen protoplasts are regulated by external and internal pH

 Patch-clamp whole-cell and single-channel recording techniques were used to investigate the regulation of outward K+ channels by external and internal protons in Brassica chinensis pollen protoplasts. Outward K+ currents and conductance were insensitive to external pH (pHo) except at pH 4.5. Maximal conductance (Gmax) for the outward K+ currents was inhibited at acidic external pH. Half-activation voltage (E1/2) for the outward K+ currents shifted to more positive voltages along with the decrease in pHo. E1/2 can be described by a modified Henderson–Hasselbalch equation expected from a single titratable binding site. The activation kinetics of the outward K+ channels was largely insensitive to pHo. An internal pH (pHi) of 4.5 significantly increased outward K+ currents and conductance. Gmax for the outward K+ currents decreased with elevations in pHi. In contrast to the effect of pHo, E1/2 was shifted to more positive voltages with elevations in pHi. The outward K+ currents, Gmax and E1/2 can be described by the modified Henderson–Hasselbalch equation. Furthermore, acidifying pHi accelerated the activation of the outward K+ currents significantly. The differences in electro-physiological properties among previously reported and currently described plant outward K+ channels may reflect differences in the structure of these channels.