Figure 6: Effect of MPC088 photoactivation on GABA-evoked currents in cerebellar PNs.

(a) Optical configuration. (b) Representative trace from a whole-cell voltage-clamp recording from a PN. The cell was held at −70 mV, and 10 μM GABA+30 μM MPC088 were applied via pressure pipette for 30 s. The cell was flashed with UV light (1 s, shuttered from a mercury arc lamp), then blue light (1 s, from a 470 nm LED) and then again with UV light (1 s). Insets expand the segments of the trace recorded when the light pulses were delivered. (c) Trace from the same cell as in b, but with exposure to 10 μM GABA alone. (d) Trace from the same cell as in b,c, but with exposure to 10 μM GABA+300 μM propofol. (e) Summary of results described in b–d. The left-hand trace shows the method used to obtain the numerical data shown at the right. The magnitude of the UV-to-blue transition was calculated as (B-UV1)/UV1; that of the blue-to-UV transition was calculated as (UV2-B)/UV2. Here, UV1, B and UV2 are, respectively, the magnitude of the current evoked by the first UV flash, the blue flash and the second UV flash, as referenced to the pre-GABA current level. The number above each condition indicates the number of cells from which data were obtained. For the negative control experiments (that is, those involving exposure to vehicle or propofol alone) in which no light-evoked current was detectable, current was measured for identical epochs at the terminations of the light pulses. Error bars represent the s.e.m. For both the blue-to-UV and the UV-to-blue transitions, the Kruskal–Wallis analysis of variance on ranks yielded P<0.005 (H>11, df=2). Post-hoc statistical tests showed that results obtained with MPC088 treatment differed significantly from those obtained under either negative control condition (Mann–Whitney rank-sum test: MPC088 versus vehicle (blue-to-UV and UV-to-blue), P=0.002; MPC088 versus propofol (blue-to-UV and UV-to-blue), P=0.014; P-values adjusted for multiple comparisons). (f) Representative trace from a cell exposed to multiple UV/blue light flashes during application of GABA and MPC088.