Large conductance Ca(2+)-activated K+ channels in the soma of rat motoneurones.
Properties of large conductance Ca(2+)-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 Ko+/(/)155 mM Ki+) and 231 +/- 4 pS in external high-Ko solution (155 mM Ko+/(/)155 mM Ki+). 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.
Safronov
B V
BV
Physiologisches Institut, Justus-Liebig-Universitaet Giessen, Germany.
Vogel
W
W
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D018999:Charybdotoxin / Q000494:pharmacology; D004594:Electrophysiology; D051036:Large-Conductance Calcium-Activated Potassium Channels; D009046:Motor Neurons / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D015221:Potassium Channels / Q000502:physiology*; D024681:Potassium Channels, Calcium-Activated; D051381:Rats
D051036:Large-Conductance Calcium-Activated Potassium Channels; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D018999:Charybdotoxin; D011188:Potassium; D002118:Calcium