Table 1

Differentiation of substrate and nonsubstrate transport inhibitors by heteroexchange

Experiment	[³H]d-Aspartate Efflux	[³H]GABA Efflux
	% of control	% of control
Control	100 ± 4	100 ± 8
l-Glutamate, 10 μM	233 ± 10^1-a	100 ± 6
GABA, 50 μM	102 ± 11	252 ± 18^c
Kainate, 100 μM	81 ± 6	104 ± 8
AMPA, 100 μM	97 ± 6	99 ± 7
NMDA, 100 μM	91 ± 3	99 ± 7
trans-ACPD, 100 μM	100 ± 10	99 ± 7
β-d,l-THA, 20 μM	167 ± 8^1-a	102 ± 5
l-trans-2,4-PDC, 15 μM	186 ± 17^1-a	96 ± 4
l-trans-2,3-PDC, 300 μM	96 ± 5	95 ± 6
DHK, 300 μM	94 ± 6	101 ± 2
l-Glutamate, 10 μM andl-trans-2,3-PDC, 300 μM	129 ± 7^b	N.D.
l-Glutamate, 10 μM and DHK, 300 μM	129 ± 8^b	N.D.
GABA, 50 μM and l-trans-2,3-PDC, 300 μM	N.D.	248 ± 28^c
GABA, 50 μM and DHK, 300 μM	N.D.	252 ± 20^c

Efflux of radiolabeled substrate from synaptosomes containing either [³H]d-ASP or [³H]GABA was determined as described in Materials and Methods and is expressed as percentage of control (i.e., efflux over a 2-min interval at 37°C in the absence of uptake inhibitors). Initial content of synaptosomes was 1552 ± 62 pmol [³H]d-ASP/mg protein or 3887 ± 263 pmol [³H]GABA/mg protein. Control efflux rates were 114 ± 4 pmol/min/mg protein for [³H]d-ASP and 354 ± 30 pmol/min/mg for [³H]GABA. Values are reported as mean ± S.E.M.,n = 4-57 duplicate determinations. Statistical comparisons were made using an Alternate Welch t test (InStat).

↵1-a p < .0005 versus [³H]d-ASP control; ^b p< .0001 versus glutamate-mediated [³H]d-ASP efflux; ^c p < .001 versus [³H]GABA control. N.D., not determined.