Technical aspects of voltage-clamping the cut-open squid giant axon.

The design of a voltage-clamp system dedicated to recording the fluctuation of sodium currents under non-stationary conditions from a leaflet of cut-open squid axon is presented. The membrane leaflet is mechanically sandwiched between the apices of two finely machined plexiglass cones which enable fluid access to each side of the membrane and a known area of membrane to be voltage-clamped. The design requirements necessary to achieve satisfactory signal resolution have been assessed in terms of the overall digitising resolution of the ADC hardware and the intrinsic and extrinsic components of the clamp-system noise. Good agreement between the predicted and measured noise performance was found. The clamp system has enabled simultaneous estimates of the single-channel conductance and channel density to be made over a much wider range of experimental conditions than previously possible.