Abstract
In potassium channels, it has been proposed that two different gates are arranged in series along the pore. To investigate the mechanism of gating, KcsA channel was studied using a modified tip-dip method and single-channel currents were analyzed using the hidden Markov model. Effect of various concentration of sucrose (10%-40%) on the gating kinetics was tested. As the concentration of sucrose increased, the single-channel conductance was decreased and the open time was remarkably prolonged. In asymmetric concentrations of sucrose, sucrose in the intracellular side was effective to control the gating. Contrarily to what has been believed, in which high concentration of non-electrolyte forced the channel closed through collapsing effect of osmotic pressure, we found that the open probability was increased. Various non-electrolytes, such as sorbitol and glycerol, were applied and similar effects were observed. Since the viscosity of these solutions varied significantly, kinetic viscous effect on gating was less likely. A gating model built from the single-channel data identified that the fast gating mode was strongly affected by non-electrolytes. Thus, it is suggested that the effect of non-electrolytes is medicated through altered hydration state of the channel upon gating. [Jpn J Physiol 54 Suppl:S68 (2004)]
