Figure 1.

Electrophysiological characterization of TaALMT1-expressing and control (i.e. not injected with cRNA) Xenopus oocytes preloaded with malate. A, Extracellular Al³⁺ induces an inward current in oocytes expressing TaALMT1. Net currents were recorded at −100 mV. The arrow indicates the time point when the ND88 bath solution (see “Materials and Methods” for detailed composition) was exchanged by ND88 solution containing 100 μm AlCl₃ (8 μm Al³⁺ activity). Cells were preloaded with malate, yielding an intracellular malate concentration of approximately 8 mm (4.5 mm mal²⁻ activity; see “Materials and Methods” for loading protocols and cytoplasmic malate determinations). Each trace was recorded from a different cell. B, Examples of families of currents from control and TaALMT1-expressing cells recorded in ND88 solution lacking or containing 100 μm AlCl₃ (8 μm Al³⁺ activity) in response to voltage pulses ranging from −140 to +100 mV in 20-mV steps (see “Materials and Methods” for detailed protocol). C, Mean I/V relationships from control (triangles) and TaALMT1-expressing (circles) oocytes recorded in the absence (white symbols) or presence (black symbols) of 100 μm AlCl₃ in ND88 solutions (n = 14). The inset highlights the inward (i.e. negative) currents. D, Left, Examples of the net TaALMT1 currents. The resulting traces were obtained by subtracting the control cell current traces from recordings for the TaALMT1-expressing cells. These recordings were obtained in ND88 solution containing 100 μm AlCl₃ (8 μm Al³⁺ activity) in response to voltage pulses ranging from −140 to +100 mV in 10-mV steps. Right, I/V relationship corresponding to the net Al³⁺-enhanced TaALMT1-mediated current calculated by subtracting the background endogenous currents recorded from control cells (in the presence of Al³⁺) from those recorded from TaALMT1-expressing cells in the presence of Al³⁺. The net current was calculated from the average currents from the relationships shown in C.