The conductance and density of sodium channels in the cut‐open squid giant axon.

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Abstract
Non-stationary Na current fluctuations in small voltage-clamped patches of cut-open squid giant axon were analysed by an ensemble-average technique to yield the single Na channel conductance .gamma.Na and the Na channel density in the patch. .gamma.Na appeared to be voltage independent over the range -30 to +40 mV and had a mean value of 4.4 .+-. 1.1 pS in 514 mM-Na//20 mM-Na at 5 kHz band width and temperature between 3.5 and 5.0.degree.C. .gamma.Na did not change significantly at band widths to 20 kHz. .gamma.Na in reduced Na solutions, 103 mM-Na//4 mM-Na, at 3.5-5.0.degree.C had a mean value of 1.2 .+-. 0.3 pS. Internal solutions containing 50 mM-tetraethylammonium (TEA) depressed both .gamma.Na and the mean Na currents by roughly the same factor, compared with solutions without TEA. The reduced .gamma.Na had a mean value of 2.2 .+-. 0.7 pS. The mean Na channel density in the standard 514 mM-Na//20 mM-Na solution was estimated to be 180 .+-. 100 .mu.m-2. The densities in the other solutions mentioned above were not significantly different from this value.