Distinct expression patterns of inwardly rectifying potassium currents in developing cerebellar granule cells of the hemispheres and the vermis

G-protein-coupled inwardly rectifying potassium (GIRK) channels play a crucial role during the migration and maturation of cerebellar
granule cells (GCs) in the vermis. In the cerebellar hemispheres, however, only minor effects on the development of GCs
are observed in mice with GIRK channel impairment. This regional difference may reflect distinct ontogenetic expression patterns
of GIRK channels. Therefore, inwardly rectifying responses in mice were characterized at different stages of development in the
vermis and the hemispheres. In the vermis, GCs in the premigratory zone (PMZ) at P7–P15 exhibit GIRK current but not constitutive
inwardly rectifying potassium (CIRK) current, and are relatively depolarized at rest. In contrast, premigratory GCs in the hemispheres
express only CIRK channels, which accounts for their more hyperpolarized resting membrane potential. Furthermore, the
pattern of voltage-dependent inward currents in the PMZ GCs of cerebellar hemispheres is consistent with a more mature stage
of development than the corresponding GCs in the vermis, resulting in robust firing properties mediated by sodium channels.
Later in development (P21–P22), CIRK current is then observed in the majority of vermis GCs. This developmental pattern,
revealed by electrophysiological recordings, was confirmed by immunohistological experiments that showed greater reactivity for
GIRK2 in the PMZ of the vermis than in the hemispheres during development (P7–P15). These findings suggest that regional differences
in development are responsible for the differential expression of inwardly rectifying potassium channels in the vermis
and in the hemispheres.