inhibitory synaptic Transmission in isolated patches of MEMBRANE FROM
CULTURED RAT SPINAL CORD AND MEDULLARY NEURONS.
Lewis, C. A. and D. S. Faber.
Department of Anatomy and Neurobiology, Medical College of Pennsylvania and
Hahnemann University, 3200 Henry Avenue, Philadelphia, PA 19129.
APStracts 3:0031N, 1996.
SUMMARY AND CONCLUSIONS
1. To quantify the variability in the characteristics of inhibitory
glycinergic and GABAergic currents at single synaptic connections between
cultured rat embryonic spinal cord or medullary neurons, we have used patch
clamp techniques to record miniature inhibitory postsynaptic currents in cell-
attached patches. Experiments were performed with the patch pipette containing
either a low calcium internal saline to allow comparison with subsequent
whole-cell recordings or external saline with tetrodotoxin, DL-2-amino-5-
phosphonovaleric acid and 6-cyano-7-nitroquinoxaline-2,3-dione, a solution
which is more appropriate for bathing a nerve terminal. 2. The mIPSCs recorded
from the synapses restricted to the cell-attached patches were characterized
by their times to peak, amplitudes, and time constants of decay. The degree of
variability in these characteristics was quantified using the following model-
independent parameters: the coefficient of variation, skewness, and kurtosis.
The distribution of time to peak values has a mean value of 5.6 +/- 0.5 ms,
the lowest coefficient of variation (0.33 +/- 0.01), is fairly symmetrical,
and has a Gaussian shape with respect to peakedness. On the other hand, both
the amplitude and decay time constant distributions are highly skewed and more
peaked than Gaussian distributions. The mean amplitude is -6.6 +/- 0.6 pA with
a coefficient of variation of 0.60 +/- 0.05, while the mean decay time
constant is 22.8 +/- 1.0 ms with a coefficient of variation of 0.81 +/- 0.03.
3. The amplitude distributions for spontaneous inhibitory currents recorded
from cell-attached patches are best fitted by the sum of multiple Gaussians.
The coefficient of variation for the first Gaussian peak fitted to the
amplitude distributions is 0.290 +/- 0.028. 4. Decay time distributions were
consistently best fitted by the sum of four Gaussians with decay constants of:
D1 = 5.7 +/- 0.2 (n=12), D2 = 11.2 +/- 0.7 (n=11), D3 = 20.6 +/- 0.8 (n=12),
and D4 = 43.8 +/- 2.3 (n=16) ms. These mean values are essentially identical
to those reported in the preceding paper for mIPSCs recorded in the whole-cell
configuration. 5. In eight neurons we were able to record mIPSCs both in cell-
attached patches and in subsequent whole-cell configurations. The properties
of mIPSCs recorded from single synapses (i.e. times to peak, amplitude, and
time constants of decay) show as much variability as those of mIPSCs recorded
subsequently in the whole-cell mode; that is, there are no statistically
significant differences in the coefficients of variation, skewness or kurtosis
for the three different distributions.
Received 14 November 1995; accepted in final form 22 January 1996.
APS Manuscript Number J720-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 February 96