Invading gastric cancer cells highly express functional Kir2.1. A, Whole-cell patch-clamp measurement showing invading XN0422 gastric cancer cells that displayed higher potassium current compared with noninvading cells. Potassium current was inhibited by barium (5 μmol/L). B, The current density–voltage (pA/pF-V) curves derived from same data presented in A with a typical characteristic of IK+. C, Higher average IK+ at 100 mV in invading gastric cancer cells than in noninvading gastric cancer cells. Data are shown as mean ± SD (n = 20; *, P < 0.05, Student t-test). D, The mRNA level of Kir family in invading and noninvading gastric cancer cells. Data are shown as mean ± SD (n = 3). E, Increased Kir2.1 mRNA expressed by gastric cancer cells with high current (IK+ > 50 pA) compared with low current (IK+ < 5 pA) gastric cancer cells as detected by qRT-PCR. Data are shown as mean ± SD (n = 6; ***, P < 0.0001, Student t test). F, Higher level of Kir2.1 protein in invading gastric cancer cells compared with noninvading gastric cancer cells as detected by Western blotting.