Figure 7.
Tonic release influence time development of transients. A, Size and shape of transients depends on tonic dopamine release. Transients were evoked by a train of five stimulations at 20 Hz. Different shades of red indicate the basal dopamine level. Dark red has C 0 = 14 nm, red has C 0 = 70 nm, and orange has C 0 = 230 nm. B, Effect of background activity on average uptake kinetics. Average kinetics based on 14 transients as shown in A (same colors). Black lines show the predictions of the Michaelis–Menten model. C, Transient characteristics as function of baseline level. Quantities were found by nonlinear curve fits to the Michaelis–Menten equation; error bars indicate 95% confidence intervals (n = 5). C1, Apparent uptake velocity, V′. C2, Apparent Michaelis–Menten constant, K′. C3, Apparent time constant, τ′. C4, Amplitude of transients. Black dashed lines show the prediction of Equation 9 (C1), Equation 10 (C2), and Equation 11 (C3).