Figure 4.

Malate efflux underlies the inward TaALMT1-mediated current. A, Mean I/V relationships obtained in TaALMT1-expressing (circles) and control (triangles) cells preloaded with malate (left) or water (right). Recordings were performed in ND96LA solution minus (white symbols) or plus (black symbols) 10 μm Al³⁺ activity (n = 10). Malate preloading resulted in an internal malate concentration increase of 8.2 mm compared with the 200 to 400 μm endogenous malate present in water-injected cells (see “Materials and Methods” for internal malate determinations). Note the different current scales between the two panels (n = 16). B, Net inward TaALMT1-mediated current obtained after subtraction of the endogenous currents recorded in control cells. The I/V relationships illustrate the magnitude and the E_rev (arrows) of the inward currents in cells preloaded with malate (left) or water (right) prior to (dashed line) and after (solid line) exposure to extracellular Al³⁺. C, Preloading cells with malate led to an increase in the magnitude of the TaALMT1-mediated inward current and a shift in E_rev (arrow and dotted lines) to more positive potentials. The I/V relationship shown corresponds to the net enhanced TaALMT1 mediated current corresponding to the difference between the current in the presence and absence of Al³⁺, calculated after subtracting the endogenous currents recorded in control cells. Currents were calculated from the relationships shown in A.