Channel blockers increase titers of Lv-Kv1.4 and Lv-TREK, but not those of Lv-GFP and Lv-HERG. (A) Ba2+ had no effect on the titer of Lv-GFP. After 293T cells were transfected with Lv-GFP and helper plasmids, they were incubated in the presence or absence of 0.3 mM BaCl2 for 48 h. The titers in the unconcentrated aliquots were determined by measuring the number of GFP-positive cell clusters after the transduction to 293T cells (n = 5). (B) Increase in Lv-Kv1.4 titer. The addition of 4-AP (0.5 mM) significantly increased the titer of Lv-Kv1.4. Because the lentiviral vectors prepared in the presence or absence of blocker were prepared concurrently, the data were analyzed with a paired t test (n = 5, p < 0.05). (C) Increase in Lv-TREK titer. Similarly, the transfected 293T cells were incubated in the presence or absence of 1 mM BaCl2, and the titers were measured (p < 0.05, n = 5). (D) No increase in Lv-HERG titer. In contrast, the addition of E-4031 did not increase the titer of Lv-HERG (n = 8).