FIG. 1.

Efficiency of dipeptidyl-peptidase-like protein (DPPL) DPPX knockdown by short-interfering RNAs (siRNAs). A: immunoblot analysis of CHO cells transfected with siRNAs or empty vector (pSUPER) at a 1:1 ratio with respect to DPPX-S cDNA. Control: cells transfected only with green fluorescent protein (GFP). Cells were harvested at 48 h posttransfection. The bar plots show the fraction of DPPX protein obtained from quantification of immunoblots after subtracting the background obtained from the control lane with respect to the value obtained in cells co-transfected with empty vector (100%). B: high sensitivity of X309 short-interfering DPPX (siDPPX) was shown by immunoblot analysis of CHO cells transfected with the increasing amounts of pSUPER-X309. The total amount of siRNA vector was kept constant at 3 μg by adding complementary amounts of empty pSUPER. Cells were harvested at 48 h posttransfection. C: examples of traces obtained at different voltages (see methods for voltage protocol) from CHO cells transfected with Kv4.2 cRNA alone (left), Kv4.2 + DPPX-S + pSUPER (center), and Kv4.2 + DPPX-S + pSUPER-X309 (right). D: peak current at +40 mV (I_max) plotted against time to peak during a depolarization to +40 mV in cells transfected with Kv4.2 alone (black squares), Kv4.2 + DPPX-S + pSUPER (blue triangles), or Kv4.2 + DPPX-S + pSUPER-X309 (red circles). E: current magnitudes recorded at 24, 48, and 72 h after transfection. Shown as blue triangles are averages (±SE) from cells transfected with Kv4.2 + DPPX-S + pSUPER at 24 h (n = 8), 48 hs (n = 16), and 72 h (n = 7). The dotted line represents the mean value for cells transfected with Kv4.2 alone (471.9 + 111.6, n = 11), which did not vary significantly with time after transfection. The red circles are individual cells transfected with Kv4.2 + DPPX-S + pSUPER-X309. Error bars represent SE.