To be revised

The "ramp clamp" was so named to describe an experiment in which the control voltage was swept with a linear increase in voltage with time (ramp) from a resting level to a strong depolarized value. The membrane current was plotted vs voltage directly and continuously rather than plotting points for the peak and steady state currents-vs-voltage for a step voltage clamp. For certain restricted rates of voltage sweep, the ramp clamp current-voltage relationship resembled the form of conventional I/V plots. More precisely, a fast ramp was used to yield a plot resembling the sodium current and a slow ramp to plot the potassium current (Moore, 1959).

Of course for other rates, the shape of the curve deviates sharply because both the sodium and potasium conductances vary with time as well as voltage and BOTH contribute to the current observed at any time. Furthermore the results were contaminated with a constant capacitive current flowing during the ramp phase. Nevertheless it was proposed as a useful way to record data very quickly. However, when Na channel kinetics are changed, for example, by:

the intrepretation of the records is difficult - `if not compromised to the point of lack of uselessness.

xx needs revision here- Fishman did know of Ik at fast sweeps.
give fishman ref here The most obvious failing with the ramp clamp experiments on squid axons showed up when the sodium conductance was blocked by the application of tetrodotoxin. While the inward current disappeared for a fast ramp, an outward current persisted at voltages above the sodium equilibrium potential! Analog simulations of this conditions showed similar plots and revealed that the apparent outward sodium current on a fast sweep was actually carried by potassium!!