Catechins from green tea modulate neurotransmitter transporter activity in Xenopus oocytes

Figures & data

Table 1. Relative effect of 40 or 50 μM (-)-epicatechin and EGCG on GAT1- and EAAC1-mediated current, respectively, and of 1 μM TGB on GAT1-mediated current at −100 mV with respect to the current in the absence of drug. Data represent averages ± SEM of N experiments

Current mediated by	(-)-Epicatechin	EGCG	Tiagabine
GAT1	1.00 ± 0.05	0.66 ± 0.08	0.34 ± 0.08
	(N = 3)	(N = 5)	(N = 3)
EAAC1	1.79 ± 0.10	1.06 ± 0.05	Ineffective
	(N = 5)	(N = 10)
Structure

Figure 1. (A, B) Original current traces in response to rectangular voltage pulses. Pulses were applied from −150 to +30 mV in 20 mV increments. Top traces are in the absence, middle traces in the presence of 100 μM GABA (A) or 300 μM glutamate (B). Lower traces show the differences of currents in the presence and absence of drug, respectively. The hatched bars indicate the time period of 20 ms used to determine mean steady-state currents. (C, D) Steady-state current–voltage dependencies determined from the above traces.

Figure 2. Protocol of a typical experiment. (A) Chart record of holding current at −60 mV illustrating the inward-directed current responses to different concentrations of GABA (deflections to the left). (B) Current–voltage dependencies of the respective GABA-induced steady-state currents determined as the difference of the currents in the presence and absence of GABA.

Figure 3. Dependence of GAT1-mediated current at −100 mV on GABA concentration. One corresponds to −415.7 ± 41.2 nA. Data point represent averages ± SEM from N = 5–11 oocytes. The line represents a fit of Equation (1) to the data with K_1/2 = 57.6 ± 3.8 μM (n = 2).

Figure 4. Effect of EGCG (A, B) and of TGB (C, D) on GAT1-mediated current (A, C) Voltage dependence of GAT1-mediated current (activated by 50 μM GABA) in the absence and presence of 100 μM EGCG (A: N = 3) and 1 μM TGB (B: N = 5). Dependence of the GAT1-mediated, steady-state current at −100 mV on EGCG (B) and TGB (D) concentration. 100% corresponds to −220 ± 11 nA (B) and −148 ± 17 (D). Data point represent averages ± SEM from N = 3 (B) and N = 5 (D) oocytes. The solid line represents a fit of Equation (1) to the data with K_1/2 values of 99 ± 14 μM (n = 1) (B) and 2.3 ± 0.8 μM (n = 1) (D).

Figure 5. Dependence of EAAC1-mediated current at −100 mV on glutamate concentration. One corresponds to 570 ± 75 nA. Data point represent averages ± SEM from N = 7 oocytes. The line represents a fit of Equation (1) to the data with K_1/2 = 82.0 ± 2.9 μM (n = 1.9).

Figure 6. Effect of epicatechin on EAAC1-mediated current (A) Voltage dependence of EAAC1-mediated current (activated by 100 μM glutamate) in the absence and presence of 50 μM epicatechin. (B) Dependence of the EAAC1-mediated current at −100 mV on (-)-epicatechin concentration. 100% corresponds to 407 ± 92 nA. Data point represent averages ± SEM from N = 5 oocytes. The solid line represents a fit of Equation (1) to the data with K_1/2 = 4.9 + 2.6 μM and maximum stimulation of 79 + 9% (n = 1).