Factors controlling the K+ conductance inChara |
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Authors: | M. J. Beilby |
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Affiliation: | (1) School of Botany, University of Cambridge, CB2 3EA Cambridge, England;(2) Present address: School of Biological Sciences, University of Sydney, 2006 Sydney, NSW, Australia |
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Abstract: | Summary Previous current/voltage (I/V) investigations of theChara K+ state have been extended by increasing the voltage range (up to +200 mV) through blocking the action potential with La3+. A region of negative slope was found in theI/V characteristics at positive PD's, similar to that already observed at PD's more negative than the resting level. These decreases in membrane currents at PD's more negative than –150 mV and at PD's close to 0 or positive are thought to arise from the K+ channel closure. Both the negative slope regions could be reversibly abolished by 0.1mm K+, 20mm Na+, more than 10mm Ca2+ or 5mm tetraethylammonium (TEA). The K+ channels are therefore blocked by TEA, closed by low [K+]o or high [Ca2+]o and are highly selective to K+ over Na+. With the K+ channels closed, the remainingI/V profile was approximately linear over the interval of 400 mV (suggesting a leakage current), but large rectifying currents were observed at PD's more positive than +50 mV. These currents showed a substantial decrease in high [Ca2+]o, sometimes displayed a slight shift to more positive PD's with increasing [K+]o and were unaffected by TEA or changes in [Na+]o. The slope of the linear part of theI/V profile was steeper in low [K+]o than in TEA or high [Na+]o (indicating participation of K+, but not Na+, in the leak current). Diethylstilbestrol (DES) was employed to inhibit the proton pump, but it was found that the leakage current and later the K+ channels were also strongly affected. |
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Keywords: | Chara corallina K+ channels I/V characteristics leakage current conductance |
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