Figure 1.

Tonic GABA_A conductance in rat hippocampal neurons increased with depolarization. A: Tonic GABA_A receptor-mediated currents at −40 mV and +40 mV. Horizontal bars indicate period of bicuculline application (10 µM, Bic) in this and subsequent panels. B: Quantification of tonic current amplitude. All-points histograms were created from current data before and after Bic application (gray bars in right hand panel). The peaks of these histograms were fit with a Gaussian equation (solid lines in right hand panel) to determine mean current amplitudes (dashed lines). Tonic current was defined as change in mean holding current produced by bicuculline. C: Current-voltage (I–V) plot from the neuron in (A). Values are means of 2–3 measurements at each potential. Tonic currents were outwardly-rectifying. D: Tonic chord conductance as a function of voltage from data illustrated in panels A–C. Tonic conductance increased in a near-linear fashion with membrane depolarization. Solid line represents a linear fit of the data (slope = 13 pS/mV). E: Mean current density as a function of voltage for all neurons tested (n=12). F: Mean capacitance-specific conductance as a function of voltage for all neurons tested (n=12). Linear fit of the data had a slope of 0.32 pS*pF⁻¹*mV⁻¹.