Sodium channel expression and assembly during development of retinal ganglion cells

Acquisition of functional Na + channels is a critical event in the development of a neuron because it allows the generation of conducted action potentials. a subunit mRNA is first detected in developing rat retina at 1% of its maximum level on embryonic day 15, 4 days after the first ganglion cells are formed. a subunit protein is detected in the axons of the ganglion cells at this time, but β1 subunits, β2 subunits, and high affinity saxitoxin binding sites are not detected until after birth. There is an approximately coordinate increase in α subunit mRNA, α, β1, and β2 subunit protein, assembled complexes of α, β1, and β2 subunits, and high affinity saxitoxin binding sites between postnatal days 7 and 21. Expression of α subunit genes is an early event in ganglion cell differentiation, and both gene transcription and posttranslational assembly are separate, ratelimiting steps in development of Na + channels.