Fig. 3.

Sialin mediates NO₃⁻/H⁺ as well as SA/H⁺ cotransporter in HSG cells. (A) Current measurement in cells perfused with medium at pH 4.0 containing 5 mM SA, NO₃⁻, or both. (B) I-V curves of the current (E_rev= 0 mV for 5 mM SA or NO₃⁻) obtained under the different conditions shown in A. (C) Intracellular pH in medium of pH 4.0 containing either SA or NO₃⁻. (D) Currents generated by substituting NO₃⁻ with glutamate (Glu) or aspartate (Asp), with other anions transported by sialin. (E and F) SA and NO₃⁻ currents induced at pH 4.0 in control HSG cells (E) and cells treated with sh-sialin (F). The y-axis scale is the same in E and F. (G) Average of data from the experiments shown in E and F. (H) Effect of expression of plasma membrane-targeted mutant of sialin L22A-L23A on NO₃⁻ and SA currents. (I) Average data and statistical evaluation for H. (J) Surface expression of sialin in WT cells and in cells transfected with scram-sh, sh-sialin, or L22A-L23A mutant (AA). (K) NO₃⁻ and SA uptake measured at 10 min after loading in HSG cells transfected with sh-sialin or scram-sh. *Values significantly different from the unmarked values (P < 0.05; n = 6).