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KMID : 0811719990030010001
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Korean Journal of Physiology & Pharmacology
1999 Volume.3 No. 1 p.1 ~ p.10
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Mechanism of Membrane Hyperpolarization by Extracellular K+ in Resistance-sized Cerebral Arterial Muscle Cell of Rabbit
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Se Hoon Kiml
Kun Moo Choi/Hoe Suk Kim/Byeong Hwa Jeon/Seok Jong Chang
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Abstract
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We sought to find out the mechanism of vascular relaxation by extracellular K+ concentration ([K+]o) in the cerebral resistant arteriole from rabbit. Single cells were isolated from the cerebral resistant arteriole, and using voltage-clamp technique barium-sensitive K+ currents were recorded, and their characteristics were observed. Afterwards, the changes in membrane potential and currents through the membrane caused by the change in [K+]o was observed. In the smooth muscle cells of cerebral resistant arteriole, ion currents that are blocked by barium, 4-aminopyridine (4-AP), and tetraethylammonium (TEA) exist. Currents that were blocked by barium showed inward rectification. When the [K+]o were 6, 20, 60, and 140 mM, the reversal potentials were ?82.7±1.0,?49.5±1.86,?26±1.14,?5.18±1.17 mV, respectively, and these values were almost identical to the calculated K+ equilibrium potential. The inhibition of barium-sensitive inward currents by barium depended on the membrane potential. At the membrane potentials of -140, -100, and -60 mV, Kd values were 0.44, 1.19, and 4.82 μM, respectively. When [K+]o was elevatedfrom 6 mM to 15 mM, membrane potential hyperpolarized to -50 mV from -40 mV. Hyperpolarization by K+ was inhibited by barium but not by ouabain. When the membrane potential was held at resting membrane potential and the [K+]o was elevated from 6 mM to 15 mM, outward currents increased; when elevated to 25 mM, inward currents increased. Fixing the membrane potential at resting membrane potential and comparing the barium-sensitive outward currents at [K+]o of 6 and 15 mM showed that the barium- sensitive outward current increased at 15 mM K+. From the above results the following were concluded. Barium-sensitive K+?channel activity increased when [K+]o is elevated and this leads to an increase in K+?outward current. Consequently, the membrane potential hyperpolarizes, leading to the relaxation of resistant arteries, and this is thought to contribute to an increase in the local blood flow of brain.
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KEYWORD
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Membrane hyperpolarization, Barium-sensitive K, _channel, Cerebral artery,
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