Single Na channels in mouse neuroblastoma cell membrane

Abstract

Single sodium channel currents were studied in mouse neuroblastoma cells. Channel conductance (γ) was 11.6±3.4 pS at 6–8°C. Unitary current amplitudes and channel activity increased with increasing temperature. The Arrhenius plot of the conductance was linear between 5 and 35°C with an activation enthalpy of 27.1 kJ/mole (Q ₁₀ =1.28). Amplitude distributions were fitted by the sum of two Gaussian functions indicating the presence of two different single channel amplitudes: smalleri ₁ and largeri ₂. The relative probability of appearance ofi ₁, which has a shorter mean open time, was higher during the early phase of depolarization (t<16 ms). The open time histograms, inactivating phase of macroscopic currents and delay time histograms were fitted by the sum of two exponentials. The distinct kinetic and steady-state parameters reflect two open states of sodium channels.