Figure 5.

Absence of the characteristics of Kir_4.1 activation kinetics in mature astrocytes. A: 100 μM Ba²⁺ brought about a 2.5 mV and 14 mV depolarization of membrane potential (V_M) in a syncytial coupled (black trace) and a freshly dissociated astrocyte (gray trace), respectively. B and C: in a syncytial coupled astrocyte, the Ba²⁺-sensitive currents remained a linear current-voltage (I-V) relationship, exhibiting neither an Mg²⁺ nor Na⁺ inhibition of outward- and inward-going currents noted in Fig. 4. D and E: in a single freshly dissociated astrocyte, 100 μM Ba²⁺ were able to substantially inhibit the passive conductance but failed to isolate a current component fitting in the activation kinetics of Kir_4.1 shown in Fig. 4, indicating a mixed expression of multiple Ba²⁺-sensitive currents other than Kir_4.1. V_C, command voltage. Modified from Ref. 29.