Verapamil blocks HERG channel by the helix residue Y652 and F656 in the S6 transmembrane domain.
OBJECTIVE
The objectives of this study were to investigate the inhibitory action of verapamil on wild-type(WT) and mutation HERG K+ channel current (I(HERG)), and to determine whether mutations in the S6 region are important for the inhibition of I(HERG) by verapamil.


METHODS
HERG channels (WT, Y652A, and F656A) were expressed in oocytes of Xenopus laevis and studied using the 2-electrode voltage- clamp technique.


RESULTS
WT HERG is blocked in a concentration-dependent manner by verapamil (half-maximal inhibition concentration [IC(50)]=5.1 micromol/L), and the steady state activation and inactivation parameters are shifted to more negative values. However, mutation to Ala of Y652 and F656 located on the S6 domain produced 16-fold and 20-fold increases in IC(50) for IHERG blockade, respectively. Simultaneously, the steady state activation and inactivation parameters for Y652A are also shifted to more negative values in the presence of the blockers.


CONCLUSIONS
Verapamil preferentially binds to and blocks open HERG channels. Tyr-652 and Phe-656, 2 aromatic amino-acid residues in the inner (S6) helix, are critical in the verapamil-binding site.
Duan
Jing-jing
JJ
Cardio-Electrophysiological Research Laboratory Medical College, Wuhan University of Science and Technology, Wuhan 430081, China.
Ma
Ji-hua
JH
Zhang
Pei-hua
PH
Wang
Xian-pei
XP
Zou
An-rou
AR
Tu
Dan-na
DN
D000818:Animals; D002121:Calcium Channel Blockers / Q000378:metabolism*; D051638:Ether-A-Go-Go Potassium Channels / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects; D009865:Oocytes / Q000166:cytology / Q000502:physiology; D018408:Patch-Clamp Techniques; D011487:Protein Conformation; D014700:Verapamil / Q000378:metabolism* / Q000494:pharmacology; D014982:Xenopus laevis
D002121:Calcium Channel Blockers; D051638:Ether-A-Go-Go Potassium Channels; D014700:Verapamil