Fig. 4.

Specificity of SNF-5-coupled amino acid-induced currents. (A) Typical recording of amino acid-induced currents in an SNF-5-expressing oocyte. The oocyte was placed in a small volume constant-flow chamber on the fifth day after cRNA injection and maintained at −50 mV holding potential using a two-electrode voltage clamp. Amino acids were applied via a multiplexing perfusion system switching from 98N basal medium to 1 mmol l⁻¹ amino acid solution in the same medium for the indicated intervals (black bars). The responses to similar concentrations of amino acid in control deionized-water-injected oocytes were <2 nA or undetectable at the presented scale (N>10, data not shown). (B) Response of an SNF-5-expressing oocyte to metabolic amino acids: betaine (Bet), taurine (Tau), and glutathione (GSSG). (C) Statistically validated responses of SNF-5-injected oocytes to 1 mmol l⁻¹ l-amino acids in Na⁺ (98N) and K⁺ (98K) media, black and gray bars, respectively. Bars are relative amplitudes of substrate-induced currents normalized versus l-Pro, mean ± s.d., N>2 different oocytes for each data point. ^#Values that are not significantly different between Na⁺ and K⁺ specific samples; ^##values that were not significantly different between control and SNF-5 injected oocytes (t-test, P>0.05, N>2). (D) Superposed current traces generated in response to 1 mmol l⁻¹ solutions of l-Met and l-Glu in 98N medium and after complete substitution of Na⁺ with a larger NMDG⁺ ion.