A large intracellular pool of inactive Na channel alpha subunits in developing rat brain.

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Abstract
An intracellular pool of Na channel .alpha. subunits was detected in developing brain cells in vivo and in vitro by phosphorylation with cAMP-dependent protein kinase, immunoprecipitation with specific antiserum, and NaDodSO4 [sodium dodecyl sulfate] gel electrophoresis or by radioimmunoassay. These .alpha. subunits are membrane-bound, contain complex carbohydrate chains and have an apparent MW of 260,000 like mature .alpha. subunits. In contrast to mature .alpha. subunits, the intracellular subunits are not covalently attached to a .beta.2 subunit, and they do not bind saxitoxin with high affinity. They comprise 67-77% of the total immunoreactive .alpha. subunit in developing rat brain cells but are not a prominent component in the adult brain. This intracellular pool of .alpha. subunits forms a ready reserve of preformed subunits for incorporation into the surface membrane during periods of active membrane biogenesis. Disulfide linkage of the .alpha. and .beta.2 subunits, insertion into the cell surface membrane and attainment of a functional conformation are closely related late events in the biogenesis of the Na channel. These processes may regulate the number of functional Na channels in the developing brain.