Blocking and modifying actions of octanol on Na channels in frog myelinated nerve

Publisher Website
Google Scholar
Abstract
The actions of externally applied n-octanol on Na channels in myelinated frog nerve fibres were studied under voltage clamp conditions. Upon octanol application peak Na inward currents declined in two phases: 90% of the reduction occurred in less than 2 min but a steady-state was reached only after 15 min. During washout the currents came to a stable level within 10 min. The reduction of Na inward currents by octanol was dependent on the amplitude and duration of prepotentials. At the resting potential (V H=0 mV) 0.4 mM octanol reduced peak Na inward currents atV=60 mV by 50%. After a prepulse of −60 mV and 50 ms duration Na currents decreased only by 20%. At a hyperpolarizing holding potential ofV H=−28 mV 0.7 mM octanol reduced peak inward Na currents to one half. Octanol depressed Na currents at all potentials by approximately the same factor. The Na reversal potentialV Na remained unchanged. 0.7 mM external octanol shifted the Na activation curvem ∞ (V) by 5 mV to more positive and the inactivation curveh ∞ (V) by 14 mV to more negative potentials. The midpoint slopes of both curves were reduced. The time constants of Na activation and inactivation at small depolarizations were decreased. The conductance γ of a single Na channel and the numberN o of conducting Na channels per node were determined from nonstationary Na current fluctuations. 0.7 mM octanol increased γ by a factor of 1.6 and reducedN o by a factor of 0.34. It is concluded that octanol blocks some Na channels and modifies the remaining unblocked channels.