The intracellular segment of the sodium channel beta 1 subunit is required for its efficient association with the channel alpha subunit.
Sodium channels consist of a pore-forming alpha subunit and auxiliary beta 1 and beta 2 subunits. The subunit beta 1 alters the kinetics and voltage-dependence of sodium channels expressed in Xenopus oocytes or mammalian cells. Functional modulation in oocytes depends on specific regions in the N-terminal extracellular domain of beta 1, but does not require the intracellular C-terminal domain. Functional modulation is qualitatively different in mammalian cells, and thus could involve different molecular mechanisms. As a first step toward testing this hypothesis, we examined modulation of brain Na(V)1.2a sodium channel alpha subunits expressed in Chinese hamster lung cells by a mutant beta1 construct with 34 amino acids deleted from the C-terminus. This deletion mutation did not modulate sodium channel function in this cell system. Co-immunoprecipitation data suggest that this loss of functional modulation was caused by inefficient association of the mutant beta 1 with alpha, despite high levels of expression of the mutant protein. In Xenopus oocytes, injection of approximately 10,000 times more mutant beta 1 RNA was required to achieve the level of functional modulation observed with injection of full-length beta 1. Together, these findings suggest that the C-terminal cytoplasmic domain of beta 1 is an important determinant of beta1 binding to the sodium channel alpha subunit in both mammalian cells and Xenopus oocytes.
Meadows
L
L
Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada.
Malhotra
J D
JD
Stetzer
A
A
Isom
L L
LL
Ragsdale
D S
DS
D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000378:metabolism; D002462:Cell Membrane / Q000502:physiology; D008322:Mammals; D008564:Membrane Potentials; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000502:physiology; D021122:Protein Subunits; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012530:Saxitoxin / Q000493:pharmacokinetics; D015222:Sodium Channels / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D014982:Xenopus laevis
D021122:Protein Subunits; D011994:Recombinant Proteins; D015222:Sodium Channels; D012530:Saxitoxin