Noise analysis to study unitary properties of transporter-associated ion channels

Excitatory amino acid transporters (EAATs) do not only mediate secondary-active glutamate uptake but also function as anion channels. We recently used macroscopic current recordings and noise analysis to determine unitary current amplitudes of anion channels associated with a neuronal EAAT isoform, EAAT4. We found that, at symmetrical NO(3)(-), EAAT4 anion channels exhibit a single channel conductance of ~1 pS in the absence as well as in the presence of glutamate. These results indicate that glutamate increases EAAT4 anion currents by modifying exclusively open probabilities, however, leaves unitary current amplitudes unaffected. Noise analysis has been developed for ion channels with a single conductance state and limitations might ensue when using this approach for transporter-associated ion channels. We here performed stochastic simulations of EAAT transporter-associated anion channels and noise analysis of simulated currents to assess the reliability and possible limitations of this technique in studying this special class of ion channels.