TY - JOUR T1 - Molecular Determinants of β<sub>1</sub> Subunit-Induced Gating Modulation in Voltage-Dependent Na<sup>+</sup> Channels JF - The Journal of Neuroscience JO - J. Neurosci. SP - 7117 LP - 7127 DO - 10.1523/JNEUROSCI.16-22-07117.1996 VL - 16 IS - 22 AU - Naomasa Makita AU - Paul B. Bennett AU - Alfred L. George Jr. Y1 - 1996/11/15 UR - http://www.jneurosci.org/content/16/22/7117.abstract N2 - Recombinant brain, skeletal muscle, and heart voltage-gated Na+ channel α subunits differ in their functional responses to an accessory β1 subunit when coexpressed inXenopus oocytes. We exploited the distinct β1 subunit responses observed for the human heart (hH1) and human skeletal muscle (hSkM1) isoforms to identify determinants of this response. Chimeric α subunits were constructed by exchanging the S5–S6 interhelical loops of each domain between hH1 and hSkM1 and then examined for effects on inactivation induced by coexpressed β1 subunit in oocytes. Substitution of single S5–S6 loops in either domain 1 (D1/S5–S6) or domain 4 (D4/S5–S6) of hSkM1 by the corresponding segments of hH1 produced channels that exhibited an attenuated response to coexpressed β1 subunit. Substitutions of both D1/S5–S6 and D4/S5–S6 in hSkM1 by the corresponding loops from hH1 completely abolished the effects of the β1 subunit on inactivation. The reciprocal chimera in which both D1/S5–S6 and D4/S5–S6 from hSkM1 were transplanted into hH1 exhibited significant β1 responsiveness (accelerated inactivation). The region within D4/S5–S6 that conferred β1 responsiveness was determined to reside primarily within an extracellular loop between the putative pore-forming segment SS2 and D4/S6. Gating modulation was also demonstrated using a chimeric β subunit consisting of the extracellular domains of β1and the transmembrane and C-terminal domains of the rat brain β2 subunit. These results suggest that the D1/S5–S6 and D4/S5–S6 loops in the α subunit and the extracellular domain of the β1 subunit are important determinants of the β1 subunit-induced gating modulation in Na+channels. ER -