μl Na⁺ channels expressed transiently in human embryonic kidney cells: Biochemical and biophysical properties

We describe the transient expression of the rat skeletal muscle μl Na⁺ channel in human embryonic kidney (HEK 293) cells. Functional channels appear at a density of ∼30 in a 10 μm² patch, comparable to those of native excitable cells. Unlike pl currents in oocytes, inactivation gating is predominantly (∼97%) fast, although clear evidence is provided for noninactivating gating modes, which have been linked to anomalous behavior in the inherited disorder hyperkalemic periodic paralysis. Sequence-specific antibodies detect a ∼230 kd glycopeptide. The majority of molecules acquire only neutral oligosaccharides and are retained within the cell. Electrophoretic mobility on SDS gels suggests the molecules may acquire covalently attached lipid. The channel is readily phosphorylated by activation of the protein kinase A and protein kinase C second messenger pathways.