Sodium channel subconductance levels measured with a new variance-mean analysis.
The currents through single Na+ channels were recorded from dissociated cells of the flexor digitorum brevis muscle of the mouse. At 15 degrees C the prolonged bursts of Na+ channel openings produced by application of the drug DPI 201-106 had brief sojourns to subconductance levels. The subconductance events were relatively rare and brief, but could be identified using a new technique that sorts amplitude estimates based on their variance. The resulting "levels histogram" had a resolution of the conductance levels during channel activity that was superior to that of standard amplitude histograms. Cooling the preparation to 0 degrees C prolonged the subconductance events, and permitted further quantitative analysis of their amplitudes, as well as clear observations of single-channel subconductance events from untreated Na+ channels. In all cases the results were similar: a subconductance level, with an amplitude of roughly 35% of the fully open conductance and similar reversal potential, was present in both drug-treated and normal Na+ channels. Drug-treated channels spent approximately 3-6% of their total open time in the subconductance state over a range of potentials that caused the open probability to vary between 0.1 and 0.9. The summed levels histograms from many channels had a distinctive form, with broader, asymmetrical open and substate distributions compared with those of the closed state. Individual subconductance events to levels other than the most common 35% were also observed. I conclude that subconductance events are a normal subset of the open state of Na+ channels, whether or not they are drug treated. The subconductance events may represent a conformational alteration of the channel that occurs when it conducts ions.
Patlak
J B
JB
Department of Physiology and Biophysics, University of Vermont, Burlington 05405.
D000704:Analysis of Variance; D000818:Animals; D004553:Electric Conductivity; D004594:Electrophysiology; D008433:Mathematics; D051379:Mice; D008807:Mice, Inbred BALB C; D009132:Muscles / Q000502:physiology; D010879:Piperazines / Q000494:pharmacology; D015222:Sodium Channels / Q000502:physiology*
D010879:Piperazines; D015222:Sodium Channels; C046261:DPI 201-106