Some kinetic and steady-state properties of sodium channels after removal of inactivation

G. S. Oxford

Research output: Contribution to journalArticle

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Abstract

To study the kinetic and steady-state properties of voltage-dependent sodium conductance activation, squid giant axons were perfused internally with either pronase or N-bromoacetamide and voltage clamped. Parameters of activation, τ(m) and gNa(V), and deactivation, τ(Na), were measured and compared with those obtained from control axons under the assumption that gNA is directly proportional to m3h of the Hodgkin-Huxley scheme. τ(m)(V) values obtained from the turn-on of I(Na) agree well with control axons and previous determinations by others. τ(Na)(V) values derived from Na tail currents were also unchanged by pronase treatment and matched fairly well previously published values. τ(m)(V) obtained from 3 x τ(Na)(V) were much larger than τ(m)(V) obtained from I(na) turn-on at the same potentials, resulting in a discontinuous distribution. Steady state In (g(Na)/g(Na)(max)-g(Na)) vs. voltage was not linear and had a limiting logarithmic slope of 5.3 mV/e-fold g(Na). Voltage step procedures that induce a second turn-on of I(Na) during various stages of the deactivation (Na tail current) process reveal quasiexponential activation at early stages that becomes increasingly sigmoid as deactivation progresses. For moderate depolarizations, primary and secondary activation kinetics are superimposable. These data suggest that, although m3 can describe the shape of I(Na) turn-on, it cannot quantitatively account for the kinetics of g(Na) after repolarization. Kinetic schemes for g(Na) in which substantial deactivation occurs by a unique pathway between conducting and resting states are shown to be unlikely. It appears that the rate-limiting step in linear kinetic models of activation may be between a terminal conducting state and the adjacent nonconducting intermediate.

Original languageEnglish (US)
Pages (from-to)1-22
Number of pages22
JournalJournal of General Physiology
Volume77
Issue number1
StatePublished - 1981
Externally publishedYes

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Sodium Channels
Axons
Pronase
Tail
Decapodiformes
Sigmoid Colon
Linear Models
Sodium

ASJC Scopus subject areas

  • Physiology

Cite this

Some kinetic and steady-state properties of sodium channels after removal of inactivation. / Oxford, G. S.

In: Journal of General Physiology, Vol. 77, No. 1, 1981, p. 1-22.

Research output: Contribution to journalArticle

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