Rubidium ions and the gating of delayed rectifier potassium channels of frog skeletal muscle.

Abstract

SUMMARY1. Unitary currents were measured through delayed rectifier potassium channels of frog skeletal muscle, under conditions where either potassium or rubidium ions carried current.2. Unitary currents were reduced in amplitude when Rb+ was the charge carrier, indicating that Rb+ permeated the channel less readily than did K+. On the other hand permeability ratios (PRb/PK) measured from the change in reversal potential upon ionic substitution were 092 for the external and 067 for the internal mouth of the channel.3. 5. The prolongation in Rb+ of tail currents under repolarization was associated with increases in the number of openings per burst and in the number of bursts during each tail.6. The implications of these results for channel gating are discussed. It is argued that an early step in channel activation is more voltage dependent than later steps.

Cation‐dependent gating of the hyperpolarization‐activated cation current in the rabbit sino‐atrial node cells.

“…3) might support this view. Such an effect was explained well by the anomalous mole fraction mechanism described in other channel types, such as the Ca2" channel (Ascher, Marty & Neild, 1978;Eckert & Chad, 1984;Hess & Tsien, 1984), the delayed rectifier K+ channel (Swenson & Armstrong, 1981;Spruce, Standen & Stanfield, 1989), the inward rectifier K+ channel (Hagiwara & Yoshii, 1979;Leech & Stanfield, 1981) and the Na+ channel (Begenisich & Cahalan, 1980 (Hagiwara, Miyazaki, Krasne & Ciani, 1977: Spruce et al 1989. It is known that the gating mechanism of the inward rectifier K+ channel is not determined by the absolute level of the membrane potential but by the deviation from the reversal potential (Saigusa & Matsuda, 1988).…”

K channel gating by an affinity-switching selectivity filter

“…Conservative point mutations in the selectivity filter have substantial effects on open state stability, a primary single-channel gating characteristic (15)(16)(17), whereas mutations at the cytoplasmic construction only affect bursting kinetics (18). Open state stability is determined by the permeating ion species, directly linking gating to selectivity (19,20). Finally, in inwardly rectifying K channels, internal Ba 2ϩ could access its binding site when the channel was closed, indicating that the gate lies within the selectivity filter (21).…”

Molecular Determinants of Gating at the Potassium Channel Selectivity Filter

“…6, right panel) that occurs when the N-terminal inactivating peptide binds to the channel and induces a sequence of conformational changes that leads to the constriction of the permeation pathway (Rasmusson et al, 1998). Likewise, several groups support the role of the permeant ion as a critical factor in the modulation of C-type inactivation (Demo and Yellen, 1992;LeMasurier et al, 2001;Lopez-Barneo et al, 1993;Shapiro and DeCoursey, 1991;Spruce et al, 1989;Swenson and Armstrong, 1981). Ions with longer occupancy in the selectivity filter (Rb + , Cs + , NH 4 + ) tend to slow-down entry into the inactivated state through a "foot in the door mechanism" in which the resident ion stabilizes the conductive conformation.…”

“…One of the first indications came from the effect of certain permeant ions on gating (Demo and Yellen, 1992;LeMasurier et al, 2001;Spruce et al, 1989;Swenson and Armstrong, 1981). Ions with longer residency times in the selectivity filter (Rb + and NH 4 + ) tend to stabilize the open conformation through a "foot in the door mechanism".…”

“…the selectivity filter) acting in concert with the opening of the inner helix bundle (Liu et al, 2001). Several pieces of evidence point to the selectivity filter as a region with a great deal of influence over the gating behaviour of K + channels, including the effect of certain permeant ions on gating (Demo and Yellen, 1992;Shapiro and DeCoursey, 1991;Spruce et al, 1989;Swenson and Armstrong, 1981), the effect of unnatural amino acid mutagenesis at the selectivity filter (Lu et al, 2001), and the role of subconducting states and specific P-loop mutants on single channel gating kinetics (Alagem et al, 2003;Chapman et al, 1997;Proks et al, 2001;Zheng and Sigworth, 1997). Gating of K + channels at the level of the selectivity filter has been traditionally associated with C-type inactivation, a slow process by which the channel enters a non-conductive conformation, and is sensitive to external K + concentration (Hoshi et al, 1991;Kiss et al, 1999;Liu et al, 1996;Lopez-Barneo et al, 1993).…”