Outward K+ channels in Brassica chinensis pollen protoplasts are regulated by external and internal pH |
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Authors: | Fan L-M Wang Y-F Wu W-H |
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Institution: | (1) Department of Plant Sciences, State Key Laboratory in Plant Physiology and Biochemistry College of Biological Sciences, China Agricultural University, Beijing, CN |
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Abstract: | Summary. 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 (G
max) for the outward K+ currents was inhibited at acidic external pH. Half-activation voltage (E
1/2) for the outward K+ currents shifted to more positive voltages along with the decrease in pHo. E
1/2 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. G
max for the outward K+ currents decreased with elevations in pHi. In contrast to the effect of pHo, E
1/2 was shifted to more positive voltages with elevations in pHi. The outward K+ currents, G
max and E
1/2 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.
Received May 7, 2002; accepted July 9, 2002; published online November 29, 2002 |
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Keywords: | : Brassica chinensis K+ channel Patch clamp pH Pollen protoplast |
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