Figure 6. Depolarizing currents elicited at 100 μM concentration: persistent current defined as A) time constant of recovery, T₅₀, or B) current remaining after removing the compound externally (washout).

A. Time constants of recovery after removal of test compounds. All agents induce a significantly slower recovery than DA except 3-des-OH DA (3) and R(−)AMPH (R1). Compounds designated with (*) or (**) and with T₅₀ values greater than 1 (dotted line) are referred to as ‘persistent’ at 100 μM; only β-PEA also passes this test at 10 μM (Fig. 3). S(+)AMPH generates a prominent ‘shelf’ with a flattened current, also seen at 10 μM in Fig. 2, while other agents have only delayed recovery times expressed as T₅₀ > 1 at this higher concentration; however, β-PEA may also show a ‘shelf’ or ‘flattening’, as shown in the inset. Data recorded at −60 mV. Note: the numbers for each compound are labeled inside the column. The symbols ** imply p < 0.001 and * p < 0.01.

B. The relative persistent currents of four compounds selected from panel A for slow recovery times are shown here as a function of concentration. The current Io is the induced depolarizing current just before washout, and Ip is the current remaining after washout just before block with cocaine. Only S(+)AMPH (S1) stands out at all concentrations; β-PEA (5), with relatively slow recovery and a ‘shelf’ similar to S(+)AMPH, has a much lower persistent current than S(+)AMPH (S1) by this definition, as do R(−)α-Me 3-des OH DA (R6) and S(+)α-Me-3-des OH (S6) at all concentrations.