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 mu M). Blockade of hERG channels was dependent on channel opening, and tonic block was minimal. Steady-state activation V-0.5 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 V-0.5 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 mu M BAPTA-AM. The S6 mutant Y652A and the pore helix mutant S631A significantly attenuated blockade by BAPTA-AM at 10 mu M 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 mu M, 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. (c) 2007 Elsevier Inc. All rights reserved.