Figure 4: Persistent potentiation and activation by MPC100 in γ-79C-expressing oocytes.

(a) GABA responses of a single oocyte before (left) and after (right) MPC100 treatment (100 μM). Right-hand waveforms recorded after ~7-min incubation with MPC100 and subsequent Ringer perfusion. (b) GABA response functions showing aggregate data (mean±s.d.; five oocytes) obtained before MPC100 treatment, and after treatment with 100 μM MPC100 and subsequent washout (~5 min). Amplitudes normalized to that elicited by 100 μM GABA before MPC100 treatment. (c) Light-dependence of persistent potentiation. Black trace: response to UV and visible light in the presence of 0.1 μM GABA, following treatment with 100 μM trans-dominant MPC100. Dotted lines i and ii highlight the difference in baseline current before (ii) versus after (i) UV illumination). Red trace: later phase of the same experiment (responses obtained after a further ~1 min Ringer perfusion). (d) Baseline currents obtained in a single experiment. Trace i: nominal response to PTX (100 μM). Traces ii, iii: PTX responses obtained after treatment with 100 μM MPC100 in the absence (ii) and presence (iii) of UV illumination. (e) Responses to UV and visible light following exposure to trans-dominant MPC100 and washout (~5 min) of free MPC100. Data obtained from a single oocyte. A period of Ringer perfusion (~1 min) separated the initial (black trace) and later (red trace) phases of the experiment. (f) Aggregate results (mean±s.d.) from experiment e and three others, each involving amplitude determinations under six sequential experimental conditions. Data normalized to the persisting shift in baseline produced by MPC100 treatment. Periods of treatment in each experiment were similar to those illustrated in e. Numbers beneath the waveforms in e denote amplitude determination conditions for the experiment shown in e. Repeated-measures analysis of variance conducted on the aggregate data yielded F(6,18)=65.290, P<0.001. Post-hoc paired-sample Student's t-tests corrected for multiple comparisons indicated significant differences produced by the initial UV, the initial high-intensity visible light (High-Vis), the second UV, and the second High-Vis illuminations (P≤0.007 for amplitude group 2 versus group 1, for 3 versus 2, for 4 versus 3, and for 6 versus 5, respectively).