Loss of Perivascular Kir4.1 Potassium Channels in the Sclerotic Hippocampus of Patients With Mesial Temporal Lobe Epilepsy

Recent experimental data in mice have shown that the inwardly rectifying K+ channel Kir4.1 mediates K+ spatial buffering in the hippocampus. Here we used immunohistochemistry to examine the distribution of Kir4.1 in hippocampi from patients with medication-refractory temporal lobe epilepsy. The selectivity of the antibody was confirmed in mice with a glial conditional deletion of the gene encoding Kir4.1. These mice showed a complete loss of labeled cells, indicating that Kir4.1 is restricted to glia. In human cases, Kir4.1 immunoreactivity observed in cells morphologically consistent with astrocytes was significantly reduced in 12 patients with hippocampal sclerosis versus 11 patients without sclerosis and 4 normal autopsy controls. Loss of astrocytic Kir4.1 immunoreactivity was most pronounced around vessels and was restricted to gliotic areas. Loss of Kir4.1 expression was associated with loss of dystrophin and alpha-syntrophin, but not with loss of beta-dystroglycan, suggesting partial disruption of the dystrophin- associated protein complex. The changes identified in patients with hippocampal sclerosis likely interfere with K+ homeostasis and may contribute to the epileptogenicity of the sclerotic hippocampus.