Different modes of operation of single sodium channels in neuroblastoma cells

Abstract

Single channel currents were obtained from voltage-dependent sodium channels in neuroblastoma cells, N1E 115, using a cell-attached variation of the patch-clamp technique. The channel density in these membranes allowed frequent registration of a “bursting mode” of individual Na channels in native form. At 10–15°C we examined prolonged bursts of Na channel openings within and between the different membrane patches. At the level of resting membrane potential (RP+10 mV) the mean channel open time was 1.40 ms, while in the “burst mode” the mean open time was 8.31 ms. The open time histogram was well fitted by a sum of two voltage-dependent exponential functions. The different time constants of the fits for histograms constructed from single openings and from openings during the burst suggest that the population of individual Na channels is heterogeneous with the mean open time following voltage dependence. The I/V curve is linear between −60 and −10 mV; the large standard deviation in the main current amplitude may indicate multiple open conformations of channels in burst openings. The results from open, closed and burst time channel kinetics indicate that the observed burst behaviour of normal Na channels is due to a different channel function mode - i.e. that the gating kinetics of single Na channels are heterogeneous and that they may change their function in a single channel level.