Blocking Kir2.1 current increased the titer of Lv-synapsinP-Kir2.1. (A and B) The titer of Lv-synapsinP-Kir2.1 was increased by blocking the Kir2.1 current. The viral vector was prepared in the presence or absence of 0.3 mM BaCl2. The titers of unconcentrated (A) and concentrated (B) viral vectors were measured in host PC12 cells. The addition of Ba2+ significantly increased the titers (*p < 0.05, **p < 0.005, Student’s t test, n = 4).