Extracellular Potassium and Astrocytic Kir4.1 Modulate Interneuron Activity in the Cerebral Cortex

Astrocyte potassium buffering through the inwardly rectifying potassium channel, Kir4.1, is a crucial and essential
function. Changes in Kir4.1 have been implicated in epilepsy, seizures, and several neurodegenerative
disorders. However, until recently it was thought that outside of pathological conditions K+e rises would be small
and cleared slowly, with their effects on neurons unclear. We recently showed that presynaptic neuronal activity
induces fast, large, and highly focal astrocyte depolarizations driven by localized increases in extracellular
potassium (K+e) and blunted by Kir4.1 activity. This raises new questions that we seek to address about how
astrocyte K+ buffering and Kir4.1 affect neuronal activity. We hypothesize that interneurons are specifically
sensitive to changes in K+e and Kir4.1 buffering, affecting their excitability, synaptic function, and network activity
while having only small effects on excitatory neurons. Interneurons are fast spiking neurons, potentially leading
to focal K+e accumulation. Interneuron action potential waveforms depend on a fast, and large
afterhyperpolarization to enable their fast spiking frequencies, potentially making them sensitive to changes in
K+e. Preliminary data suggests that GABA clearance and GABAergic network activity are modulated by Kir4.1.
Interneuron activity, especially of parvalbumin interneurons play a crucial role in ictal activity, able to both restrain
ictal activity and pathologically enhance its spread. We hypothesize that K+e enhances PV-hyperactivity and
enhances ictal spread in an in-vitro model of seizure. Conversely, Kir4.1 will inhibit this ictal activity, acting
through PV-INs. If successful this proposal would give a better understanding of how K+e and astrocytic
potassium buffering through Kir4.1 affects neuronal activity, especially GABAergic activity. This can lead to a
better understanding of how Kir4.1 and astrocytes contribute to pathological conditions.

Grant Number: 3R01NS127819-04S1
NIH Institute/Center: NIH
Principal Investigator: Moritz Armbruster