Figure 3: Characteristics of formate and lactate uptake in Xenopus oocytes.

The (a) pH-dependence and (b) susceptibility to inhibition of PfFNT-induced formate and lactate uptake. Uptake was measured over 10 min at an extracellular formate or lactate concentration of 1 mM, except where specified otherwise. The data were averaged from those obtained in n independent experiments, each from different days, using eggs from different frogs, where n was: (a) 6 for [¹⁴C]formate (black bars) and 4 for [¹⁴C]lactate (white bars); (b) 4–8 for [¹⁴C]formate (black bars) and 4 for [¹⁴C]lactate (white bars). In b, the extracellular pH was 6.4 and the potential competing substrates (formate and lactate; 10 mM) and inhibitors (100 μM) were added to the oocytes at the same time as the [¹⁴C]formate or [¹⁴C]lactate. In both panels, uptake is expressed relative to that measured at pH 6.4 in the absence of competing substrate or inhibitors. The asterisks denote statistical significance of the apparent differences between [¹⁴C]formate or [¹⁴C]lactate uptake measured under each of the different conditions tested and that measured in the relevant controls: *P<0.05; **P<0.01; ***P<0.001.