Guide to Electrophysiological Recording
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49
Chapter 4
microelectrodes may introduce a number of undesirable properties. For best results,
the microelectrode voltage must settle rapidly after a current pulse, and the
microelectrode must be able to pass current without large changes in resistance.
The important factors that need to be considered are discussed below.
Electrode Glass
Borosilicate glass is often used; however, through trial and error one type of
glass supplied by a specific glass manufacturer may have been shown to yield
the best results. It is suggested that the literature be consulted prior to
selecting glass for recording.
Tip Resistance
Tip resistance (R
e
) should be as low as possible and consistent with good
impalements of the cell. Low values of R
e
allow for greater stability and faster
settling time of the microelectrode.
Stability
R
e
of most microelectrodes changes with time and with current passing. R
e
is affected not only by the magnitude of the current but also by its polarity.
In general, microelectrodes of lower resistance are more stable during
current passing than those of higher resistance.
Settling time
The decay time constant of the microelectrode voltage after a current pulse
depends strongly on R
e
. Thus, lower R
e
values produce faster settling
times. As well, high R
e
values are sometimes associated with a slow final
decay even after the electrode capacitance has been eliminated. (See next
page.)
