A 3-D Approach to Voltage Clamp Data

The purpose of this report is to introduce a holistic approach to voltage clamp data. By voltage clamping excitable membranes, in the whole-cell or single-channel level, it is possible to define four basic types of parameters: kinetic (e.g. time and rate constants), "size" (e.g. current, conductance and permeability), selectiviO, to certain ions over others and dependence of these parameters on various stimuli (e.g. membrane potential and drugs). Analysis of voltage clamp data is based on two elementary viewpoints: (1) current induced by clamping the membrane to a specific holding potential as a function of time (I-t) and (2) an 1V curve which is the current as a function of holding potential at a specified point in time. These parameters and the techniques to derive them have served elecrophysiologists very successfully for more than 40 years now and the amount of data and characterized conductance published so far is immense. The approach presented here is different, aimed at illustrating the gestalt nature of excitable membrane activity under voltage clamp conditions, beyond time and voltage domains, it is based on transition from 2-D handling of voltage clamp data to 3-D, defining the IV-t space of electrical activity of the membrane~;. It is very important that the reader see the following discussion and examples as a possible extension of the conventional way of voltage clamp data analysis, rather than an alternative.