AJP - Cell Physiology, Vol 266, Issue 3 C853-C869, Copyright © 1994 by American Physiological Society
Analysis of decaying unitary currents in on-cell patches of cells with a high membrane resistance
J. H. Ravesloot, M. J. van Putten, K. Jalink and D. L. Ypey
Department of Physiology and Physiological Physics, Leiden University Faculty of Medicine, The Netherlands.
Under nonideal voltage-clamp conditions, unitary currents in the
cell-attached patch (CAP) configuration of the patch-clamp technique are
decaying instead of rectangular. From these data, four parameters can be
determined when multiple identical channels are present. We analyzed an
electrical equivalent circuit of the CAP configuration. This analysis
yielded, for single-channel resistance, attached-cell membrane resistance,
patch resistance, and attached-cell membrane capacitance, a set of
different equations to calculate their values from these four parameters.
To choose the most robust equation, those that yielded the same
resistor/capacitance were compared on the basis of their sensitivity for
inevitable deviations of the parameters from their nominal values. The
results of our theoretical study are of methodological interest: 1) because
they confirm that, under special conditions, CAP measurements can be used
to measure electrical membrane properties of intact cells (this is
important inasmuch as the CAP is the only configuration in which the
cytoplasm of cells remains undisturbed) and 2) because we identify the
level of voltage clamp and the equations with which the electrical
properties can be determined with optimal accuracy.
