AJP - Cell Physiology, Vol 246, Issue 3 339-C346, Copyright © 1984 by American Physiological Society
Electronic device for microelectrode recordings in epithelial cells
J. F. Garcia-Diaz, S. Stump and W. M. Armstrong
A device is described that permits continuous measurement of
electrophysiological parameters in epithelial tissues in the open-circuit
mode. Transepithelial potential (VT) and microelectrode (either
conventional or ion-selective) potential (VM) are directly measured.
Application of transepithelial current pulses allows continuous monitoring
of transepithelial resistance (RT) and the ratio between the changes in VM
and VT induced by these pulses. Measurement of this ratio, which under some
circumstances reflects the apical fractional resistance of the cellular
pathway, is important in assessing membrane damage during microelectrode
impalement and/or as an index that the microelectrode tip is inside a cell.
This is particularly useful when the change in VM during impalement is
small. Application of 0.5-nA current pulses through open-tip
microelectrodes allows continuous recording of the microelectrode
resistance (RM). In epithelia where the individual cells are electrically
coupled this permits acceptable impalements (RM remains nearly constant) to
be distinguished from those affected by tip potential artifacts due to
plugging of the microelectrode tip (RM increases after penetration of the
cell membrane). The device provides compensation for the IR voltage drop in
the solution between the potential measuring salt bridges and the
epithelial surfaces. The microelectrode electrometer has an input impedance
greater than 10(15) and is provided with stray capacitance neutralization.
