Table I.
Summary of the expression and transport activity of wild-type and mutant MCT1 expressed in Xenopus laevis oocytes in the presence and absence of WT- and mutant basigin. Where given, Vmax and Km values (±SE) were determined from the initial rates of transport of L-lactate determined using BCECF fluorescence as described under Methods. Four oocytes were used in each case and L-lactate was added at 2.5, 5, 10, 20 and 40 mM. Data analysis was performed as described previously (Manning Fox et al. 2000). Where no transport could be detected using BCECF confirmation was made by determining the uptake of 0.5 mM L-[14C]-lactate at 10 min as described under Methods. Transport was indicated when uptake was significantly greater than in water injected oocytes, but in no case in which no BCECF response was detected was this observed. nd: not determined.
| Transport measured using BCECF | Plasma membrane expression determined using: | |||||
|---|---|---|---|---|---|---|
| Oocyte injection | Detectable | Km±SE (mM) | Vmax±SE (ΔF.min−1) | Western blot | Sections | |
| WT-MCT1 | Yes | 3.52±0.23 | 0.42±0.007 | Yes | Yes | |
| R306E-MCT1 | No | – | – | No | No | |
| D302R/R306E-MCT1 | No | – | – | Yes | Yes | |
| R306K-MCT1 | No | – | – | Yes | Yes | |
| WT-MCT1+WT-basigin | Yes | 2.94±0.16 | 0.36±0.005 | Yes | Yes | |
| WT-MCT1+E218Q-basigin | Yes | 2.73±0.21 | 0.48±0.009 | Yes | Yes | |
| R306E-MCT1 + E218R-basigin | No | – | – | No | No | |
| D302R/R306E-MCT1 + E218R-basigin | No | – | – | Yes | Yes | |
| R306K-MCT1 + E218R-basigin | No | – | – | Yes | Yes | |
| R86Q-MCT1 | Yes | 8.79±1.5 | 0.42±0.034 | Yes | nd | |
| R86E-MCT1 | Yes | 6.48±1.5 | 0.67±0.050 | Yes | nd | |