Beta1-subunit modulates the Nav1.4 sodium channel by changing the surface charge.
Voltage-gated sodium channels, comprised of a pore-forming alpha-subunit and additional regulatory (beta) subunits, play a critical role in regulation of neuronal excitability. Mechanisms of regulation of beta-subunits remain elusive. We have tested the functional effects of beta1 sodium channel subunit on surface charges as a mechanism for channel modulation. HEK-293 cell lines permanently transfected with the sole rat skeletal muscle sodium channel alpha-subunit (Nav1.4), or co-expressing the sodium channel alpha-subunit and beta1-subunit were studied with the whole-cell mode of the patch-clamp technique. At physiological extracellular Ca2+ concentration (2 mM), expression of beta1-subunit did not produce any significant effect on the voltage-dependent properties of sodium currents. However, a shift of half-activation potentials of sodium channel by changing the extracellular Ca2+ was potentiated when beta1 was co-expressed with alpha-subunit. In contrast, the expression of beta1-subunit did not affect the Ca2+ binding to the open or to the closed sodium channel pore, difference of the effect provoked by extracellular Ca2+ could therefore be attributed to an increased in negative surface charge determined by the presence of beta1-subunit. These data are in agreement with the hypothesis of a modulation of the sodium current by the expression of the highly sialylated beta1-subunit, which would alter the channel gating by increasing the density of surface negative charges in the vicinity of the sodium channel voltage sensing machinery.
Ferrera
Loretta
L
Istituto di Biofisica, CNR, Via De Marini 6, Genova, Italy.
Moran
Oscar
O
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D006801:Humans; D015640:Ion Channel Gating; D008433:Mathematics; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D012530:Saxitoxin / Q000378:metabolism; D015222:Sodium Channels / Q000235:genetics / Q000378:metabolism*
D009124:Muscle Proteins; D021122:Protein Subunits; C466180:Scn4a protein, rat; D015222:Sodium Channels; D012530:Saxitoxin; D002118:Calcium