Slow changes in membrane permeability and long‐lasting action potentials in axons perfused with fluoride solutions

Abstract

SUMMARY1. Voltage clamp experiments were carried out on squid giant axons which were perfused internally with 300 mM-NaF +sucrose and placed in K-free artificial sea-water at 16-17' C. On stepwise depolarization ( V = -38-5 to 68 mV) the Na conductance gNa rapidly reached a peak value and then declined to a new level; this 'maintained' level was slowly inactivated in an exponential manner with a rate constant which varied from 0*3 to 1.1 sec-1. This process was not influenced appreciably by replacing 50 mM-NaF with KF.2. On repolarization to a potential which varied between -73 and -101 mV the slow inactivation was removed with a rate constant of 0-11-0-73 sec-1.3. Prolonged depolarization also produced a slow inactivation of the ability of the membrane to give a transient increase in gNa. This effect developed at a rate about 1 2 that associated with the inactivation of the 'maintained' component; on repolarization, recovery of the peak 9Na was 1-2 times as fast as recovery of the 'maintained' gNa* 4. In experiments on fibres perfused with 300 mM-KF after internal NaF had removed the usual delayed K conductance, depolarization resulted in an outward current which developed in an exponential manner with a time constant of a fraction of a second. The equilibrium potential for this component was more negative than -50 mV.5. Long-lasting action potentials were computed on the basis of the above slow changes and, except for the period of final repolarization, were

Prolonged Sodium Channel Inactivation Contributes to Dendritic Action Potential Attenuation in Hippocampal Pyramidal Neurons

“…"Slow" inactivation of Na ϩ channels has been described previously in several neuronal preparations (Narahashi, 1964;Adelman and Palti, 1969;Chandler and Meves, 1970;Schauf et al, 1976;Rudy, 1978Rudy, , 1981Belluzi and Sacchi, 1986;Ogata et al, 1990;Ruben et al, 1992;Colbert and Johnston, 1996b;Fleidervish et al, 1996). In some cases the rates of both inactivation and recovery are comparably slow, whereas in other cases, as we describe here, entry into the slow inactivated state is faster than recovery from this state.…”

Removal of sodium channel inactivation in squid axon by the oxidant chloramine-T.

“…The slow inactivation process, like the fast inactivation process, also attenuates the sodium conductance but with a much longer time constant (Adelman and Palti, 1969 ;Chandler and Meves, 1970;Schauf et al, 1976). Pronase and NBA do not remarkably alter slow inactivation after removing fast sodium inactivation (Rojas and Rudy, 1976 ;Oxford et al, 1978).…”

Sodium channel permeation in squid axons. I: Reversal potential experiments.

“…With Na inside the axon, the inactivation gating process was often incomplete (Chandler & Meves, 1970) CONCENTRATION-DEPENDENT Na CHANNEL SELECTIVITY 229 500 mM-NH4 outside. Currents are just inward at 79 mV and outward at 89 mV.…”