Current-blockade-dependent increase in the titer of Lv-Kir2.1. (A and B) The Lv-KirDN titer was higher than the Lv-Kir2.1 titer. The titers were determined with aliquots prepared before (unconcentrated) and after (concentrated) centrifugal concentration. The titers of unconcentrated and concentrated Lv-Kir-DN were both significantly higher than those of unconcentrated and concentrated Lv-Kir2.1 (n = 5; *p < 0.05, **p < 0.01, Student’s t test). (C and D) Blocking the Kir2.1 current increased the titer of Lv-Kir2.1. After plasmid transfection, the 293T cells were incubated in the presence or absence of 0.3 mM BaCl2 for 48 h. The addition of BaCl2 significantly increased the titers of both the unconcentrated and concentrated Lv-Kir2.1 (n = 5; p < 0.05, Student’s t test).