Figure 8. Effects of avian β2-subunit on the properties of 4:61 and 4:3 α-subunit isoforms.

A, voltage activation in 5 μM Ca²⁺ for a 4:61 α-subunit co-expressed with different β-subunits. Each set of points is the mean current (I), normalized to its maximum value (I_max), and has been fitted with a Boltzmann function (eqn (1)). Fitting parameters for V_½ and slope factor V_ε, and the number of experiments averaged for each condition were: α: -44 mV, 17 mV, 3; α+ bovine β: -155 mV, 21 mV, 1; α+ ccβ2 (quail): -119 mV, 21 mV, 3; α+ ggβ2 (chicken): -128 mV, 21 mV, 3. B, normalized tail currents measured at -80 mV holding potential for 4:61 α-subunit alone, or α-subunit co-expressed with quail β2 (α+ ccβ2). Time constants of decay of the tail current were 3.2 ms (α) and 37 ms (α+ ccβ2). C, voltage activation in 5 μM Ca²⁺ for 4:3 α alone and when co-expressed with quail β-subunit (α+ ccβ2). Boltzmann fitting parameters for V_½ and V_ε, and the number of experiments averaged for each condition were: α: 1 mV, 18 mV, 4; α+ ccβ2 (quail): -53 mV, 27 mV, 4. D, normalized tail currents measured at -50 mV holding potential for 4:3 α-subunit alone, or α-subunit co-expressed with quail β2 (α+ ccβ2). Time constants of decay of the tail currents were 3.1 ms (α) and 21 ms (α+ ccβ2). In both A and C, bars are ± 1 s.e.m.