The membrane permeable calcium chelator BAPTA-AM directly blocks human ether a-go-go-related gene potassium channels stably expressed in HEK 293 cells

BAPTA-AM is a well-known membrane permeable Ca2+ chelator. The present study found that BAPTA-AM rapidly and reversibly suppressed human ether a-go-go-related gene (hERG or Kv11.1) K+ current, human Kv1.3 and human Kv1.5 channel currents stably expressed in HEK 293 cells, and the effects were not related to Ca2+ chelation. The externally applied BAPTA-AM inhibited hERG channels in a concentration-dependent manner (IC50: 1.3 μM). Blockade of hERG channels was dependent on channel opening, and tonic block was minimal. Steady-state activation V0.5 of hERG channels was negatively shifted by 8.5 mV (from −3.7 ± 2.8 of control to −12.2 ± 3.1 mV, P < 0.01), while inactivation V0.5 was negatively shifted by 6.1 mV (from −37.9 ± 2.0 mV of control to −44.0 ± 1.6 mV, P < 0.05) with application of 3 μM BAPTA-AM. The S6 mutant Y652A and the pore helix mutant S631A significantly attenuated blockade by BAPTA-AM at 10 μM causing profound blockade of wild-type hERG channels. In addition, BAPTA-AM inhibited hKv1.3 and hKv1.5 channels in a concentration-dependent manner (IC50: 1.45 and 1.23 μM, respectively), and the blockade of these two types of channels was also dependent on channel opening. Moreover, EGTA-AM was found to be an open channel blocker of hERG, hKv1.3, hKv1.5 channels, though its efficacy is weaker than that of BAPTA-AM. These results indicate that the membrane permeable Ca2+ chelator BAPTA-AM (also EGTA-AM) exerts an open channel blocking effect on hERG, hKv1.3 and hKv1.5 channels.