Modulation of delayed rectifier K+ channel activity by external K+ ions in Xenopus axon.
The effect of external K+ ions upon the activation of delayed rectifier K+ channels was studied in demyelinated amphibian nerve fibres by means of the patch-clamp technique. In external 105 mM K+ solution (high-Ko) macroscopic K+ currents activated at more negative potentials (approximately -15 mV) than in external Ringer (2.5 mM K+). Since the rapid substitution of external Ringer with high-Ko solution at holding potentials of -70 mV and -60 mV directly activated K+ concentration from 5 mM to 10,20,50 and 105 mM gradually increased the open probability of the channels. Although Rb+ ions were less permeant through the channels, they were more potent in their interaction with the binding site and shifted K+ channel activation to more negative potentials. In contrast, external Cs+ ions had only a weak effect on the binding site. Thus, external K+ ions at physiological concentrations modulate the activation of delayed rectifier K+ channels at potentials between -90 mV and -60 mV.
Safronov
B V
BV
Physiologisches Institut, Justus-Liebig-Universität, Aulweg 129, D-35392 Giessen, Germany.
Vogel
W
W
D000818:Animals; D001369:Axons / Q000187:drug effects* / Q000502:physiology; D002586:Cesium / Q000494:pharmacology; D004553:Electric Conductivity; D009994:Osmolar Concentration; D011188:Potassium / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology; D012413:Rubidium / Q000494:pharmacology; D014981:Xenopus
D015221:Potassium Channels; D002586:Cesium; D012413:Rubidium; D011188:Potassium