Fig. 2.

Effect of inhibitors of G protein-coupled receptor kinase-2 (GRK2) and dynamin on long-duration dopamine (DA) application. Relative change in the firing rate (mean ± S.E.M.) is plotted as a function of time. In experiments similar to those shown in Fig. 1, the effect of DA at each time point was normalized by subtracting the change in firing rate (%) at the 5-minute time point. (A) effect of β-ARK1 inhibitor on long-duration application of DA. A concentration of DA that produced more than 50% inhibition at 5-minute time point was applied for 40 minutes. Dopamine (▪, [DA] = 4.45 ± 1.25 μM, n = 10) alone initially inhibited the firing rate, and this inhibition statistically significantly reversed with time (one-way repeated measures ANOVA, F_(7,63) = 5.96, P < 0.05). In the presence of β-ARK1 inhibitor (300 μM), no reversal of DA inhibition was observed; DA statistically significantly inhibited the firing rate over time (●, [DA] = 5.2 ± 1.2 μM, n = 9) (one-way repeated measures ANOVA, F_(7,56) = 3.23, P < 0.05). (B) effect of dynamin inhibitors dynasore or MiTMAB on long-duration application of DA. The effect of DA alone (▪ and dashed line) from Fig. 2A is shown for comparison. In the presence of dynasore (800 μM) in the recording pipette, DA did not produce the inhibition reversal (▾, [DA] = 6.64 ± 1.58 μM, n = 7) (one-way repeated measures ANOVA, F_(7,42) = 1.29, P > 0.05). In the presence of MiTMAB (400 μM) in the recording pipette, DA produced a statistically significant inhibition in the firing rate, with no reversal (●, [DA] = 7.5 ± 1.12 μM, n = 5) (one-way repeated measures ANOVA, F_(7,28) = 5.46, P < 0.05).