Table 1.

Potentiating actions of steroids on GABAA receptors

Configuration Preincubation Pipette Bath OT3 Fraction OT3 Fraction CT3 n
Cell-attached 7.6 ± 3.0 0.19 ± 0.13 0.29 ± 0.02 8
Inside-out 5.9 ± 1.2 0.22 ± 0.13 0.21 ± 0.10 4
Cell-attached 1 μm ACN 19.8 ± 3.4* 0.42 ± 0.08* 0.06 ± 0.03*** 3
Cell-attached 1 μm ACN 32.3 ± 7.9*** 0.35 ± 0.12 (NS, 0.11) 0.06 ± 0.02*** 4
Cell-attached 1 μm ACN 24.0 ± 7.7*** 0.46 ± 0.08*** 0.08 ± 0.03*** 7
Inside-out 1 μm ACN 15.5 ± 1.9** 0.37 ± 0.10 (NS, 0.15) 0.12 ± 0.02* 5
Inside-out 1 μm ACN 5 mm CDX 6.5 ± 1.5 (NS: 1.0) 0.18 ± 0.09 (NS, 1.0) 0.28 ± 0.05 (NS, 0.24) 4
Inside-out 1 μm ACN 19.4 ± 6.1** 0.29 ± 0.14 (NS, 0.79) 0.10 ± 0.01* 4
1 μm
Cell-attached Alexa-3α5αP 8.5 ± 2.9 (NS, 1.0) 0.16 ± 0.13 (NS, 1.0) 0.23 ± 0.03* 7
Inside-out 1 μm Alexa-3α5αP 15.2 ± 5.7* 0.49 ± 0.07** 0.09 ± 0.01** 4
10 μm
Cell-attached NBD-3α5αP 21.3 ± 8.4** 0.38 ± 0.11* 0.13 ± 0.07*** 5
  • In each case, the pipette solution contained 50 μm GABA in addition to the indicated steroid. The open and closed duration histograms each showed three exponential components when activity was elicited by 50 μm GABA, as described previously (Steinbach and Akk, 2001). Previous studies have indicated that potentiating steroids have their predominant effects on the mean duration of the long-duration open-time component (OT3), the fraction of openings in that component (fraction OT3), and on the fraction of closed periods in the long-duration component (fraction CT3) (Akk et al., 2004). The fraction of openings in the long duration component is the most variable experimental parameter, which we believe is the reason why ACN, in some conditions, increases the fraction OT3 but not significantly (e.g., lines 4,6, and 8). The columns list, respectively, the configuration of the recording, the presence or absence of preincubation of intact cells, the drugs dissolved in the pipette solution (to which the extracellular surface of the receptors is exposed), and the drugs dissolved in the solution in the bath outside the pipette during the recording are shown. The next columns list the mean (±1 SD) of the mean OT3, fraction OT3, fraction CT3, and the numbers of recordings in given condition. Statistical analysis was performed using ANOVA with pair-wise comparison to control group with two-tailed Dunnet's correction (Systat 7.0; SSPS, Chicago, IL). *p < 0.05, **p < 0.01, and ***p < 0.001. NS, Nonsignificant; CDX, methyl-β-cyclodextrin. Two control groups were used; for comparison with cell-attached records, the data obtained with 50 μm GABA for cell-attached records (line 1) was used, whereas analogous data for excised patches (line 2) was used as control for data from excised patches.