Abstract
Background and Purpose A second-generation antihistamine, terfenadine, is known to induce arrhythmia by blocking hERG channels. In this study, we have shown that terfenadine also inhibits the activity of G-protein-gated inwardly rectifying K+ (GIRK) channels, which regulate the excitability of neurons and cardiomyocytes. To clarify the underlying mechanism(s), we examined the effects of several antihistamines on GIRK channels and identified the structural determinant for the inhibition. Experimental Approach Electrophysiological recordings were made in Xenopus oocytes and rat atrial myocytes to analyse the effects of antihistamines on various GIRK subunits (K(ir)3.x). Mutagenesis analyses identified the residues critical for inhibition by terfenadine and the regulation of ion selectivity. The potential docking site of terfenadine was analysed by molecular docking. Key Results GIRK channels containing K(ir)3.1 subunits heterologously expressed in oocytes and native GIRK channels in atrial myocytes were inhibited by terfenadine and other non-sedating antihistamines. In K(ir)3.1 subunits, mutation of Phe137, located in the centre of the pore helix, to the corresponding Ser in K(ir)3.2 subunits reduced the inhibition by terfenadine. Introduction of an amino acid with a large side chain in K(ir)3.2 subunits at Ser148 increased the inhibition. When this residue was mutated to a non-polar amino acid, the channel became permeable to Na+. Phosphoinositide-mediated activity was also decreased by terfenadine. Conclusion and Implications The Phe137 residue in K(ir)3.1 subunits is critical for inhibition by terfenadine. This study provides novel insights into the regulation of GIRK channels by the pore helix and information for drug design.
| Original language | English |
|---|---|
| Pages (from-to) | 3161-3179 |
| Number of pages | 19 |
| Journal | British Journal of Pharmacology |
| Volume | 176 |
| Issue number | 17 |
| Early online date | 22 May 2019 |
| DOIs | |
| Publication status | Published - Sept 2019 |
Funding
We thank Ms. C. Naito and T. Yamamoto for technical assistance and all members in Kubo laboratory for discussion. Ci‐VSP cDNA was kindly provided by Dr Y. Okamura (Osaka University, Japan). iCeMS is supported by World Premier International Research Center Initiative (WPI), MEXT, Japan. This study was supported by the Hiroshi and Aya Irisawa Memorial Promotion Award for Young Physiologists (to I‐S.C.) from the Physiological Society of Japan, the Japan Society for the Promotion of Science KAKENHI Grants JP18K15020 (to I‐S.C.), JP17H04021 (to Y.K.), and JP26220206 (to M.U.) and also supported by the Israeli Science Foundation Grant 1248/15 (to E.R.). E.R. is the incumbent of the Charles H. Hollenberg Professorial Chair. I‐S.C. and Y.K. designed the study and experiments. I‐S.C. and C.L. performed all experiments using Xenopus oocytes and data analyses. I‐S.C. isolated rat atrial myocytes, and M.T. performed patch‐clamp recording from atrial myocytes and data analyses. I.K. and E.R. performed molecular docking analyses and interpreted the data. I‐S.C., M.U., and Y.K. contributed to the initial research of screening of a small‐molecule library. I‐S.C. and Y.K. wrote the paper, and all authors revised the paper and confirmed the final version.
All Science Journal Classification (ASJC) codes
- Pharmacology