INHIBITORY SYNAPTIC TRANSMISSION IN ISOLATED PATCHES OF MEMBRANE FROMCULTURED RAT SPINAL-CORD AND MEDULLARY NEURONS

1. To quantify the variability in the characteristics of inhibitory gl ycinergic and GABAergic currents at single synaptic connections betwee n cultured rat embryonic spinal cord or medullary neurons, we have use d patch-clamp techniques to record miniature inhibitory postsynaptic c urrents (mIPSCs) 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-c yano-7-nitroquinoxaline-2,3-dione, a solution that is more appropriate for bathing a nerve terminal. 2. The mIPSCs recorded from the synapse s 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 with the use of th e 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 (SE) ms, has the lowest coefficient of var iation (0.33 +/- 0.01), is fairly symmetrical, and has a Gaussian shap e with respect to peakedness. On the other hand, both the amplitude an d decay time constant distributions are highly skewed and more peaked than Gaussian distributions. The mean amplitude is -6.6 +/- 0.6 pA wit h a coefficient of variation of 0.60 +/- 0.05, whereas 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 s um of multiple Gaussians. The coefficient of variation for the first G aussian 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 as follows: D1 = 5.7 +/- 0.2 ms (n = 12), D2 = 11.2 +/- 0.7 ms (n = 11), D3 = 20.6 +/- 0.8 ms (n = 12 ), and D4 = 43.8 +/- 2.3 ms (n = 16). These mean values are essentiall y identical to those reported in the preceding paper for mIPSCs record ed in the whole cell configuration. 5. In eight neurons we were able t o record mIPSCs both in cell-attached patches and in subsequent whole cell configurations. The properties of mIPSCs recorded from single syn apses (i.e., times to peak, amplitude, and time constants of decay) sh ow as much variability as those of mIPSCs recorded subsequently in the whole cell mode; that is, there are no statistically significant diff erences in the coefficients of variation, skewness, or kurtosis for th e three different distributions.