Figure 6. Effect of β‐subunits on Na_V current inactivation in Ins1 and HEK cells.

A, relative mRNA expression of Scn1b, Scn2b, Scn3b and Scn4b in control Ins1 cells transfected with a scramble siRNA or β₃ siRNA (n = 3 preparations). B, voltage dependence of inactivation (h _∞) of endogenous Na_V currents from control (black; n = 22, from 3 preparations) and β₃ siRNA treated Ins1 cells (red; n = 26 from 3 preparations). The curves represent a double Boltzmann fit to the data. C, voltage dependence of Na_V1.7 current inactivation when the α‐subunit is co‐expressed with β₃‐subunit (black; n = 9) in Ins1 cells. Dashed red curve represents voltage dependence of Na_V1.7 current inactivation when the α‐subunit is co‐expressed with β₁‐ and β₂‐subunits in Ins1 cells (data shown in Fig. 3). The curves represent a double Boltzmann fit to the data. Arrow indicates a component of inactivation occurring at positive membrane potentials. D, as in C but for Na_V1.3 (black; n = 11). E, voltage dependence of Na_V1.7 current inactivation when the α­subunit is co­expressed with β₃‐subunit (black; n = 9) or GFP alone (red; n = 12) in HEK cells. The curves represent a single Boltzmann fit to the data. F, as in E, but for Na_V1.3 (black, n = 12; red; n = 10). V _h and k value for the respective conditions are given in Table 2. [Color figure can be viewed at http://wileyonlinelibrary.com]