Figure 1.

Characteristics of astrocyte passive conductance. A, DIC image of an astrocyte in the CA1 stratum radiatum during single-astrocyte dual-patch whole-cell recording, with two recording electrodes (shadows) sealed on the cell somata. While the conventional whole-cell recording was performed in one of the electrodes (the left electrode in A), the actual membrane potential (V_M) change following the delivery of command voltages was recorded by the second electrode simultaneously (right electrode in A). B, Command voltage pulse protocol: 200 ms test voltages were stepped from −180 mV to +20 mV with an increment of 20 mV from a holding potential of −80 mV. C, E, The whole-cell currents recorded from the left electrode and actual membrane potentials V_M recorded from the right electrode, respectively. D, Superimposing the current–command voltage relationship (I–V_C) and current–membrane potential relationship (I–V_M) from the same dual-patch recording revealed an ∼80% deficit of V_M from the expected V_C in voltage-clamp recording. The outward rectifying GHK currents generated by using the same chemical gradient of K⁺ in the recording solutions ([K⁺]_i/[K⁺]_o = 140/3.5 mm) is also shown in E, indicating a considerable deviation of the passive conductance from the expected GHK constant field rectification. As the GHK fit assumed only membrane permeability for the K⁺ ion, the GHK fit yielded a reversal potential of −93 mV, differing from the actual reversal potential of −87 mV measured from the dual-patch-recorded astrocyte.