Figure 1.
Glutamate-transporter mediated inward currents in cultured pinealocytes. A, Top, Family of currents activated by rapid application of 1 mm l-aspartate (left) or 1 mm l-glutamate (right) at membrane potentials between −80 and +40 mV in 20 mV steps. Solutions were applied to the lifted cell with exchange within a few milliseconds. Each trace is the mean of four records. All recordings were from the same cell with CsCl-based internal solution. Bottom, Current–voltage (I–V) relationships of peak currents evoked by l-aspartate (□) or l-glutamate (■) fitted with third-order polynomials. B, Average current density at V = −80 mV with several agonists of glutamate transporters and iGluRs applied at 1 mm, except AMPA and KA at 0.5 mm. Measured peak currents were divided by the capacitance of each cell. For l-, d-aspartate and l-glutamate, only cells showing current were included in the analysis. The NMDA application included 10 μm glycine, and external Mg2+ ions were omitted. C–E, Concentration dependence of currents activated by three excitatory amino acids normalized to the value with 10 mm in each cell. The averages were fitted with the Hill equation (see Materials and Methods). Half-maximal effective concentrations (Hill coefficient) are 89 μm (1.1), 73 μm (1.2), 306 μm (0.7) for l-aspartate, l-glutamate, and d-aspartate, respectively. Shown is the mean of three to four cells at −80 mV with CsCl-based internal solution. Error bars indicate SEM.