Fig. 2.

siRNA depletion of α₂δ-1 changes current kinetics and voltage dependence of cardiac L-type Ca²⁺ currents and AP duration. (A) Representative current traces in response to 200-ms test pulses to voltages between −50 and +80 mV in 10-mV increments recorded from dysgenic myotubes cotransfected with GFP-α_1C and either control or α₂δ-1-siRNA. (B and C) Current-to-voltage curves show that, in myotubes expressing α₂δ-1 siRNA, the peak current amplitude is reduced by 36% (B) and that the voltage-dependence of activation is shifted by +9 mV (P < 0.0001) (C). Fitting the current traces with a triple exponential function reveals two components of activation and one of inactivation. (D and E) Depletion of α₂δ-1 increases the contribution of the slow activation component without changing its specific time constant. (F and G) The third kinetic component reveals that α₂δ-1 depletion doubles the time constant of inactivation. (H) Current clamp recordings in GFP-α_1C + control siRNA expressing dysgenic myotubes reveal APs with cardiac shape. In α₂δ-1-depleted myotubes (gray trace) the duration of the AP plateau is significantly prolonged. (I) In the box plots, the boxes contain 50% and the vertical bars 99% of data points; central dots represent the mean; horizontal lines represent the median; asterisks represent extreme values. Error bars represent the SEM.