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Abstract:
ATP-sensitive potassium channels (K-ATP channels) directly couple the energy state of a cell to its excitability, are activated by hypoxia, and have been suggested to protect neurons during disturbances of energy metabolism such as transient ischemic attacks or stroke. Molecular studies have demonstrated that functional K-ATP channels are octameric protein complexes, consisting of four sulfonylurea receptor proteins and four pore-forming subunits which are members of the Kir6 family of inwardly rectifying potassium channels. Here we show, using specific antibodies against the two known pore- forming subunits (Kir6.1 and Kir6.2) of K-ATP channels, that only Kir6.1 and not Kir6.2 subunits are expressed in astrocytes. In addition to a minority of neurons, Kir6.1 protein is present on hippocampal, cortical, and cerebellar astrocytes, tanycytes, and Bergmann glial cells. We also provide ultrastructural evidence that Kir6.1 immunoreactivity is primarily localized to distal perisynaptic and peridendritic astrocyte plasma membrane processes, and we confirm the presence of functional K-ATP channels in Bergmann glial cells by slice-patch-clamp experiments. The identification of Kir6.1 as the principal pore-forming subunit of plasma membrane K-ATP channels in astrocytes suggests that these glial K-ATP channels act in synergy with neuronal Kir6.2-mediated K-ATP channels during metabolic challenges in the brain.
