External monovalent cations that impede the closing of K channels.

Abstract

We have examined the effects of a variety of monovalent cations on K channel gating in squid giant axons. The addition of the permeant cations K, Rb, or Cs to the external medium decreases the channel closing rate and causes a negative shift of the conductance-voltage relationship. Both of these effects are larger in Rb than in K. The opening kinetics of the K channel are, on the other hand, unaffected by these monovalent cations. Other permeant species, like NH 4 and TI, slightly increase the closing rate, whereas the relatively impermeant cations Na, Li, and Tris have little or no effect on K channel gating . The permeant cations have different effects on the reversal potential and the shape of the instantaneous current-voltage relationship . These effects give information about entry and binding of the cations in K channels . Rb, for example, enters the pore readily (large shift of the reversal potential), but binds tightly to the channel interior, inhibiting current flow . We find a correlation between the occupancy of the channel by a monovalent cation and the closing rate, and conclude that the presence of a monovalent cation in the pore inhibits channel closing, and thereby causes a leftward shift in the activation-voltage curve. In causing these effects, the cations appear to bind near the inner surface of the membrane .

Modulation of delayed rectifier K+ channel activity by external K+ ions inXenopus axon

“…2C). A similar effect of a greater increase in the K § conductance in high-Ko solution than would be expected from a simple shift of the fitting curve has also been reported for squid axons [21].…”

“…There are, however, some indications that the gating of delayed rectifier K + channels can be influenced by external monovalent cations. In squid giant axons, high concentrations of K + and Rb + cause a negative shift of the activation curve [21]. The effect of external Rb + ions was further investigated in the frog node of Ranvier [23] and frog skeletal muscle [28].…”

“…Rb § is known to permeate K + channels well, whereas external Cs § is an almost impermeant ion [16]. Both ions have been shown to slow the deactivation kinetics of delayed rectifier K + channels in squid axons [21]. These two ion species were used also in our experiments.…”

Single voltage‐activated Na+ and K+ channels in the somata of rat motoneurones.

“…In our experiments the scatter of inactivation time constants for A-channels was also large, but this most probably resulted from the modification of one channel type rather than from existence of two different types of A-channels, since the whole-cell K+ currents had only one fast component in the inactivation kinetics. Potassium DR-channels Delayed-rectifier K+ channels are involved in the repolarization phase of the action potential in the membrane of rat motoneurones (Takahashi, 1990 (Matteson & Swenson, 1986;Safronov & Vogel, 1995 (Beckh & Pongs, 1990).…”

Shaker B K+ conductance in Na+ solutions lacking K+ ions: a remarkably stable non‐conducting state produced by membrane depolarizations.

“…Potassium channels form a highly diverse group, with a large variety of gating mechanisms and kinetics, but having in common the ability to sharply select K+ over Nae ions (Hille, 1992 (Swenson & Armstrong, 1981;Armstrong & Matteson, 1986;Matteson & Swenson, 1986).…”