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

• Published in: The Journal of membrane biology Vol. 170; no. 2; pp. 103 - 119
• Main Authors: Wegner, L.H, Boer, A.H. de
• Format: Journal Article
• Language: English
• Published: United States 15.07.1999
• 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
• ISSN: 0022-2631; 1432-1424
• DOI: 10.1007/s002329900541

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.