Activation Kinetics of the K+ Outward Rectifying Conductance (KORC) in Xylem Parenchyma Cells from Barley Roots

Activation Kinetics of the K+ Outward Rectifying Conductance (KORC) in Xylem Parenchyma Cells... The activation kinetics of outward currents in protoplasts from barley root xylem parenchyma was investigated using the patch-clamp technique. The K+ outward rectifying conductance (KORC), providing the main pathway for K+ transport to the xylem, could be described in terms of a Hodgkin-Huxley model with four independent gates. Gating of KORC depended on voltage and the external K+ concentration. An increase in the external K+ concentration resulted in a shift in the voltage dependence of gating. This could be explained by a K+ dependence of the rate constant β for channel closure, indicating binding of K+ to a regulatory site exposed to the bath. Occasionally, KORC was observed to inactivate; this inactivation occurred and vanished spontaneously. In some of the whole cell and excised patch recordings, a stepwise increase in outward current was observed upon a depolarizing voltage pulse, indicating that several populations of `sleepy' channels existed in the plasma membrane that activated with a certain lag time. It is discussed whether this observation can be explained by a putative subunit, which retards channel activation, or by a scheme of cooperative gating. A quantitative description of outward rectifying K+ channels in xylem parenchyma cells is a major step forward towards a mathematical model of salt transport into the xylem. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

Activation Kinetics of the K+ Outward Rectifying Conductance (KORC) in Xylem Parenchyma Cells from Barley Roots

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Publisher
Springer-Verlag
Copyright
Copyright © Inc. by 1999 Springer-Verlag New York
Subject
Life Sciences; Biochemistry, general; Human Physiology
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s002329900541
Publisher site
See Article on Publisher Site

Abstract

The activation kinetics of outward currents in protoplasts from barley root xylem parenchyma was investigated using the patch-clamp technique. The K+ outward rectifying conductance (KORC), providing the main pathway for K+ transport to the xylem, could be described in terms of a Hodgkin-Huxley model with four independent gates. Gating of KORC depended on voltage and the external K+ concentration. An increase in the external K+ concentration resulted in a shift in the voltage dependence of gating. This could be explained by a K+ dependence of the rate constant β for channel closure, indicating binding of K+ to a regulatory site exposed to the bath. Occasionally, KORC was observed to inactivate; this inactivation occurred and vanished spontaneously. In some of the whole cell and excised patch recordings, a stepwise increase in outward current was observed upon a depolarizing voltage pulse, indicating that several populations of `sleepy' channels existed in the plasma membrane that activated with a certain lag time. It is discussed whether this observation can be explained by a putative subunit, which retards channel activation, or by a scheme of cooperative gating. A quantitative description of outward rectifying K+ channels in xylem parenchyma cells is a major step forward towards a mathematical model of salt transport into the xylem.

Journal

The Journal of Membrane BiologySpringer Journals

Published: Jul 15, 1999

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