AJP - Cell Physiology, Vol 263, Issue 6 C1234-C1240, Copyright © 1992 by American Physiological Society
Na channel kinetics remain stable during perforated-patch recordings
D. J. Wendt, C. F. Starmer and A. O. Grant
Department of Medicine, Duke University Medical Center, Durham, North Carolina 27706.
The results of studies on modulation of Na channel function are often
difficult to interpret due to time-dependent changes in channel kinetics.
Although the "tight-seal" whole cell voltage-clamp technique has proved
very useful in studying the properties of the cardiac Na current, the
spontaneous shift of parameters of inactivation and activation gating to
more negative potential is a serious limitation to the use of the
technique. The shifts are believed to result from changes in the
intracellular milieu effected by dialysis; moreover, use of a variety of
different anions and cations in the internal micropipette solution has not
obviated the problem. The perforated-patch technique permits low-resistance
intracellular access without free dialysis between the intracellular
solution and the recording micropipette. We have compared steady-state
inactivation and peak current-voltage relationship of whole cell Na
currents measured with the conventional whole cell and perforated-patch
techniques in rabbit atrial myocytes at 17 degrees C. Although gating
parameters shifted to more negative potentials when recorded with the
conventional technique, stable kinetics could be observed for up to 150 min
with the perforated-patch technique. The potential for one-half Na channel
inactivation was -73 +/- 5.1 mV and is consistent with measurements made
using indirect techniques such as upstroke velocity measurements. The fact
that the intracellular milieu is left relatively intact makes the approach
attractive for studying modulation of the Na current by neurotransmitters
and hormones.
