Figure 5.

Effect of d-aspartate and dihydrokainate on inhibition of transport of S440C and S443C in a cysteine-less background. HeLa cells expressing single-cysteine S440C or S443C transporters were preincubated with 150 mM choline chloride or 150 mM NaCl for 5 min in the absence or presence of 0.15 mM MTSET. Where indicated, 1 mM d-aspartate, GABA, or DHK was added during the preincubation. It should be noted that only one control (choline chloride without MTSET) is shown, because all the others (without methanethiosulfonate reagent) had similar values. The cells were washed twice and assayed for sodium-dependent d-[³H]aspartate uptake for 10 min. The results are given as the percentage of transport in the presence of MTSET (ET) relative to transport in the absence of the sulfhydryl reagent. Each bar is the mean ± SE of three different experiments. The control values for single-cysteine 440C and 443C transporters were 48.1% ± 7.8 and 77.8% ± 7.8 of that of the cysteine-less GLT-1, respectively. The latter was not inhibited by MTSET under any of the conditions (data not shown).