Activation kinetics of the K+ outward rectifying conductance (KORC) in xylem parenchyma cells from barley roots

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 m...

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Bibliographic Details
Published in:The Journal of membrane biology 1999-07, Vol.170 (2), p.103-119
Main Authors: Wegner, L.H, Boer, A.H. de
Format: Article
Language:English
Subjects:
Electric Conductivity
electric current
electrical conductance
Electrophysiology
Hordeum - cytology
Hordeum - physiology
Hordeum vulgare
Ion Channel Gating
ion transport
Patch-Clamp Techniques
Plant Roots - cytology
potassium
Potassium - pharmacology
Potassium - physiology
Potassium Channels - physiology
Reaction Time
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Summary: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 beta 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.
ISSN:0022-2631
1432-1424
DOI:10.1007/s002329900541