Throughout the brain, the potassium channel Kv4.2 regulates signal propagation in dendrites and action potential properties in subtypes of neurons. In adult rodents Kv4.2 is expressed predominantly in two bands in the inner plexiform layer (IPL) and in retinal ganglion cell (RGC) somas (Klumpp et al. [15]; Pinto and Klumpp [20]), suggesting a role regulating the activity of specific subtypes of RGCs. To understand the role of Kv4.2 in the regulation of the activity of RGCs during development we determined the developmental expression pattern of Kv4.2 immunoreactivity (Kv4.2-IR). At P4-6 Kv4.2-IR appeared diffusely throughout the IPL in cross-sectioned retinas. From postantal day 10 (P10) through adult there was an additional pair of brighter Kv4.2-IR bands between the ChAT bands that had a reticular pattern in flat-mounted retinas. Kv4.2-IR was not present in somas at P4-6, but appeared in ganglion cell layer (GCL) somas beginning at P10. The fraction of somas expressing Kv4.2 in the GCL was about 8% at P10-11, decreased to 5% at P20-21, then increased to 9% in adult retinas. The restriction of Kv4.2 expression to less than 10% of the GCL somas and the specificity of expression in the IPL suggest that Kv4.2 regulates activity in one or a few functional subtypes of RGCs. The pattern of Kv4.2-IR through postnatal development indicates that Kv4.2-mediated currents are important for development in a subset of RGCs, especially around P10 as the bipolar cells mature.
