Macroscopic and microscopic properties of a cloned glutamate transporter/chloride channel

The behavior of a Cl^- channel associated with a glutamate transporter was studied using intracellular and patch recording techniques in Xenopus oocytes injected with human EAAT1 cRNA. Channels could be activated by application of glutamate to either face of excised membrane patches. The channel exhibited strong selectivity for amphipathic anions and had a minimum pore diameter of ~5Å. Glutamate flux exhibited a much greater temperature dependence than Cl^- flux. Stationary and nonstationary noise analysis was consistent with a sub-femtosiemen Cl^- conductance and a maximum channel P(o) << 1. The glutamate binding rate was similar to estimates for receptor binding. After glutamate binding, channels activated rapidly followed by a relaxation phase. Differences in the macroscopic kinetics of channels activated by concentration jumps of L-glutamate or D-aspartate were correlated with differences in uptake kinetics, indicating a close correspondence of channel gating to state transitions in the transporter cycle.