Chemical modification of potassium channel gating in frog myelinated nerve by trinitrobenzene sulphonic acid.

Abstract

SUMMARY1. We investigated the actions ofexternally applied trinitrobenzene sulphonic acid (TNBS) on the K currents of voltage-clamped frog myelinated nerve fibres. TNBS treatment irreversibly slowed the tail currents for K channel closing up to 10-fold. Time constants for the tail currents appear shifted 60-80 mV in the hyperpolarizing direction following TNBS treatment.2. The time course of K channel opening was unaffected for depolarizing pulses to potentials positive to -20 mV. For smaller pulses to potentials between -80 and -30 mV the activation time course was slower following TNBS treatment.3. TNBS had little or no effect on the steady-state conductance-voltage relation of K channels determined from tail current amplitude. The instantaneous currentvoltage relation for K channels and potency ofblock by external TEA were unaffected by TNBS.4. K tail currents showed fast and slow components both before and after TNBS treatment. Reaction with TNBS caused the fast component to decline in amplitude and the slow component to increase both in magnitude and time constant. The rate of reaction increased with increasing pH.5. Full expression ofaltered K channel kinetics depends upon the ionic composition of the external solution. Tail currents were up to 10-fold slower when measured in 1 7-5 mM-K than when measured with 80 % of the external K replaced by Na.6. The differential effects ofTNBS on K channel closing and opening were modelled in a three-state kinetic scheme, with an increase in the energy barrier for closing an open channel following TNBS treatment.

The effects of rubidium ions on components of the potassium conductance in the frog node of Ranvier.

“…Previously this inflexion has only been observed in conductance-voltage curves (Palti et al 1980;Dubois, 1981 b;Cahalan & Pappone, 1983) but it may also be seen in the current-voltage relations from sensory fibres when Er is shifted to more positive potentials by the application of an impermeant cation, such as Cs+, internally (Fig. 10).…”

“…4 are shown in Fig. 6 Cahalan & Pappone, 1983;Beam & Donaldson, 1983). However, the time constant of the slow component (Tr) was little affected by Rb+ (Fig.…”

“…A slowing effect of high [K+]. on channel closing has been observed (Stiihmer & Conti, 1979;Swenson & Armstrong, 1981;Cahalan & Pappone, 1983;Cahalan et al 1985) but this effect is more marked in the presence of external Rb+ (Arhem, 1980;Swenson & Armstrong, 1981;Cahalan & Pappone, 1983;Beam & Donaldson, 1983;Spruce, Standen, Stanfield & Wilson, 1984;Cahalan et al 1985).…”

“…Cahalan & Pappone (1983) proposed an alternative model for the slowing action of external Rb+ and trinitrobenzene sulphonic acid (TNBS) on deactivation using a single energy barrier model for the gating process. The effect of external Rb+ was to reduce the energy of the open state relative to the energy of transition to the closed state.…”

The inactivating K+ current in GH3 pituitary cells and its modification by chemical reagents.

“…Modification of inactivation by these agents has also been manifest at the single-channel level and has aided in discrimination of gating models (Patlak & Horn, 1982). Similar approaches in the study of K+ channels have been more limited and have primarily revealed effects on activation gating (Shrager, 1974;Cahalan & Pappone, 1983;Pallota, 1985;Spires, Eatock, Nealey & INACTIVA TING K+ CURRENT AND ITS MODIFICATION Begenisich, 1988). We thus further report our initial attempts at probing the molecular basis of this K+ channel inactivation with chemical agents which previously have yielded useful information about Na+ channel inactivation.…”