Figure 4.

Modulation of Ca²⁺ currents by β_1a in dysgenic myotubes expressing the wild-type or Y366S mutant α_1S subunit. Patch-clamp recordings of myotubes transfected with α_1S (a) or α_1S-Y366S (b) with (β⁺) and without (β⁻) β_1a plus GFP as an expression marker are shown. The left panels show representative current traces for step depolarizations from −40 mV to +20 mV and +40 mV (asterisks). The right panels show the average I/V curves for the peak current densities (n, number of analyzed myotubes; when the current did not peak during the 1-s pulse the current value at the end of the pulse was used). In both myotubes expressing α_1S and myotubes expressing α_1S-Y366S, the peak current density is significantly (P < 0.05) increased when β_1a is coexpressed.