Expression of membrane transporters in cane toad Bufo marinus oocytes

Membrane transport proteins (transporters and ion channels) have been extensively expressed in amphibian oocytes. The aims of this study were to determine whether oocytes from the cane toad Bufo marinus could be used as an alternative expression system to the broadly used Xenopus laevis oocytes. mRNAs encoding plasma membrane transporters NaSi-1 and sat-1 (sulphate transporters), NaDC-1 (dicarboxylate transporter), SGLT-1 (Na(+)/glucose cotransporter) and rBAT and 4F2 hc (amino acid transporters) were injected into B. marinus oocytes. All led to significant induction of their respective transport activities. Uptake rates were comparable with those in X. laevis oocytes, with the exception of rBAT, which was able to induce amino acid uptake only in X. laevis oocytes, suggesting that rBAT may require an endogenous X. laevis oocyte protein that is absent from B. marinus oocytes. Transport kinetics were determined for the NaSi-1 cotransporter in B. marinus oocytes, with identical results to those obtained in X. laevis oocytes. NaSi-1 specificity for the Na(+) cation was determined, and the anions selenate, molybdate, tungstate, oxalate and thiosulphate could all inhibit NaSi-1-induced sulphate transport. This study demonstrates that cane toad oocytes can be used successfully to express plasma membrane proteins, making this a viable heterologous system for the expression of proteins.