Large Conductance Ca2+-activated K+ Channels in the Soma of Rat Motoneurones

Large Conductance Ca2+-activated K+ Channels in the Soma of Rat Motoneurones Properties of large conductance Ca2+-activated K+ channels were studied in the soma of motoneurones visually identified in thin slices of neonatal rat spinal cord. The channels had a conductance of 82 ± 5 pS in external Ringer solution (5.6 mm K+ o //155 mm K+ i ) and 231 ± 4 pS in external high-K o solution (155 mm K+ o //155 mm K+ i ). The channels were activated by depolarization and by an increase in internal Ca2+ concentration. Potentials of half-maximum channel activation (E50) were −13, −34, −64 and −85 mV in the presence of 10−6, 10−5, 10−4 and 10−3 m internal Ca2+, respectively. Using an internal solution containing 10−4 m Ca2+, averaged KCa currents showed fast activation within 2–3 msec after a voltage step to +50 mV. Averaged KCa currents did not inactivate during 400 msec voltage pulses. External TEA reduced the apparent single-channel amplitude with a 50% blocking concentration (IC50) of 0.17 ± 0.02 mm. KCa channels were completely suppressed by externally applied 100 mm charybdotoxin. It is concluded that KCa channels activated by Ca2+ entry during the action potential play an important role in the excitability of motoneurones. The Journal of Membrane Biology Springer Journals

Large Conductance Ca2+-activated K+ Channels in the Soma of Rat Motoneurones

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Copyright © Inc. by 1998 Springer-Verlag New York
Life Sciences; Biochemistry, general; Human Physiology
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