Inhibitory Effective Perturbations of Cilobradine (DK-AH269), A Blocker of HCN Channels, on the Amplitude and Gating of Both Hyperpolarization-Activated Cation and Delayed-Rectifier Potassium Currents
Cilobradine (CIL, DK-AH269), an inhibitor of hyperpolarization-activated cation current (<i>I</i><sub>h</sub>), has been observed to possess pro-arrhythmic properties. Whether and how CIL is capable of perturbing different types of membrane ionic currents existing in electric...
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MDPI AG
2020-03-01
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| Series: | International Journal of Molecular Sciences |
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| Online Access: | https://www.mdpi.com/1422-0067/21/7/2416 |
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| author | Te-Ling Lu Te-Jung Lu Sheng-Nan Wu |
| author_facet | Te-Ling Lu Te-Jung Lu Sheng-Nan Wu |
| author_sort | Te-Ling Lu |
| collection | DOAJ |
| description | Cilobradine (CIL, DK-AH269), an inhibitor of hyperpolarization-activated cation current (<i>I</i><sub>h</sub>), has been observed to possess pro-arrhythmic properties. Whether and how CIL is capable of perturbing different types of membrane ionic currents existing in electrically excitable cells, however, is incompletely understood. In this study, we intended to examine possible modifications by it or other structurally similar compounds of ionic currents in pituitary tumor (GH<sub>3</sub>) cells and in heart-derived H9c2 cells. The standard whole-cell voltage-clamp technique was performed to examine the effect of CIL on ionic currents. GH<sub>3</sub>-cell exposure to CIL suppressed the density of hyperpolarization-evoked <i>I</i><sub>h</sub> in a concentration-dependent manner with an effective IC<sub>50</sub> of 3.38 μM. Apart from its increase in the activation time constant of <i>I</i><sub>h</sub> during long-lasting hyperpolarization, the presence of CIL (3 μM) distinctly shifted the steady-state activation curve of <i>I</i><sub>h</sub> triggered by a 2-s conditioning pulse to a hyperpolarizing direction by 10 mV. As the impedance-frequency relation of <i>I</i><sub>h</sub> was studied, its presence raised the impedance magnitude at the resonance frequency induced by chirp voltage. CIL also suppressed delayed-rectifier K<sup>+</sup> current (<i>I</i><sub>K(DR)</sub>) followed by the accelerated inactivation time course of this current, with effective IC<sub>50</sub> (measured at late <i>I</i><sub>K(DR)</sub>) or <i>K</i><sub>D</sub> value of 3.54 or 3.77 μM, respectively. As the CIL concentration increased 1 to 3 μM, the inactivation curve of <i>I</i><sub>K(DR)</sub> elicited by 1- or 10-s conditioning pulses was shifted to a hyperpolarizing potential by approximately 10 mV, and the recovery of <i>I</i><sub>K(DR)</sub> inactivation during its presence was prolonged. The peak Na<sup>+</sup> current (<i>I</i><sub>Na</sub>) during brief depolarization was resistant to being sensitive to the presence of CIL, yet to be either decreased by subsequent addition of A-803467 or enhanced by that of tefluthrin. In cardiac H9c2 cells, unlike the CIL effect, the addition of either ivabradine or zatebradine mildly led to a lowering in <i>I</i><sub>K(DR)</sub> amplitude with no conceivable change in the inactivation time course of the current. Taken together, the compound like CIL, which was tailored to block hyperpolarization-activated cation (HCN) channels effectively, was also capable of altering the amplitude and gating of <i>I</i><sub>K(DR)</sub>, thereby influencing the functional activities of electrically excitable cells, such as GH<sub>3</sub> cells. |
| first_indexed | 2024-03-10T20:46:44Z |
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| spelling | doaj.art-4571acf8c7c64066b89a752d8c81016a2023-11-19T20:15:13ZengMDPI AGInternational Journal of Molecular Sciences1661-65961422-00672020-03-01217241610.3390/ijms21072416Inhibitory Effective Perturbations of Cilobradine (DK-AH269), A Blocker of HCN Channels, on the Amplitude and Gating of Both Hyperpolarization-Activated Cation and Delayed-Rectifier Potassium CurrentsTe-Ling Lu0Te-Jung Lu1Sheng-Nan Wu2School of Pharmacy, China Medical University, Taichung 40402, TaiwanDepartment of Medical Laboratory Science and Biotechnology, Chung Hwa University of Medical Technology, Tainan 71703, TaiwanInstitute of Basic Medical Sciences, National Cheng Kung University Medical College, Tainan 70101, TaiwanCilobradine (CIL, DK-AH269), an inhibitor of hyperpolarization-activated cation current (<i>I</i><sub>h</sub>), has been observed to possess pro-arrhythmic properties. Whether and how CIL is capable of perturbing different types of membrane ionic currents existing in electrically excitable cells, however, is incompletely understood. In this study, we intended to examine possible modifications by it or other structurally similar compounds of ionic currents in pituitary tumor (GH<sub>3</sub>) cells and in heart-derived H9c2 cells. The standard whole-cell voltage-clamp technique was performed to examine the effect of CIL on ionic currents. GH<sub>3</sub>-cell exposure to CIL suppressed the density of hyperpolarization-evoked <i>I</i><sub>h</sub> in a concentration-dependent manner with an effective IC<sub>50</sub> of 3.38 μM. Apart from its increase in the activation time constant of <i>I</i><sub>h</sub> during long-lasting hyperpolarization, the presence of CIL (3 μM) distinctly shifted the steady-state activation curve of <i>I</i><sub>h</sub> triggered by a 2-s conditioning pulse to a hyperpolarizing direction by 10 mV. As the impedance-frequency relation of <i>I</i><sub>h</sub> was studied, its presence raised the impedance magnitude at the resonance frequency induced by chirp voltage. CIL also suppressed delayed-rectifier K<sup>+</sup> current (<i>I</i><sub>K(DR)</sub>) followed by the accelerated inactivation time course of this current, with effective IC<sub>50</sub> (measured at late <i>I</i><sub>K(DR)</sub>) or <i>K</i><sub>D</sub> value of 3.54 or 3.77 μM, respectively. As the CIL concentration increased 1 to 3 μM, the inactivation curve of <i>I</i><sub>K(DR)</sub> elicited by 1- or 10-s conditioning pulses was shifted to a hyperpolarizing potential by approximately 10 mV, and the recovery of <i>I</i><sub>K(DR)</sub> inactivation during its presence was prolonged. The peak Na<sup>+</sup> current (<i>I</i><sub>Na</sub>) during brief depolarization was resistant to being sensitive to the presence of CIL, yet to be either decreased by subsequent addition of A-803467 or enhanced by that of tefluthrin. In cardiac H9c2 cells, unlike the CIL effect, the addition of either ivabradine or zatebradine mildly led to a lowering in <i>I</i><sub>K(DR)</sub> amplitude with no conceivable change in the inactivation time course of the current. Taken together, the compound like CIL, which was tailored to block hyperpolarization-activated cation (HCN) channels effectively, was also capable of altering the amplitude and gating of <i>I</i><sub>K(DR)</sub>, thereby influencing the functional activities of electrically excitable cells, such as GH<sub>3</sub> cells.https://www.mdpi.com/1422-0067/21/7/2416cilobradinehyperpolarization-activated cation currentdelayed-rectifier K<sup>+</sup> currentimpedance magnitude analysiscurrent kineticspituitary cell |
| spellingShingle | Te-Ling Lu Te-Jung Lu Sheng-Nan Wu Inhibitory Effective Perturbations of Cilobradine (DK-AH269), A Blocker of HCN Channels, on the Amplitude and Gating of Both Hyperpolarization-Activated Cation and Delayed-Rectifier Potassium Currents International Journal of Molecular Sciences cilobradine hyperpolarization-activated cation current delayed-rectifier K<sup>+</sup> current impedance magnitude analysis current kinetics pituitary cell |
| title | Inhibitory Effective Perturbations of Cilobradine (DK-AH269), A Blocker of HCN Channels, on the Amplitude and Gating of Both Hyperpolarization-Activated Cation and Delayed-Rectifier Potassium Currents |
| title_full | Inhibitory Effective Perturbations of Cilobradine (DK-AH269), A Blocker of HCN Channels, on the Amplitude and Gating of Both Hyperpolarization-Activated Cation and Delayed-Rectifier Potassium Currents |
| title_fullStr | Inhibitory Effective Perturbations of Cilobradine (DK-AH269), A Blocker of HCN Channels, on the Amplitude and Gating of Both Hyperpolarization-Activated Cation and Delayed-Rectifier Potassium Currents |
| title_full_unstemmed | Inhibitory Effective Perturbations of Cilobradine (DK-AH269), A Blocker of HCN Channels, on the Amplitude and Gating of Both Hyperpolarization-Activated Cation and Delayed-Rectifier Potassium Currents |
| title_short | Inhibitory Effective Perturbations of Cilobradine (DK-AH269), A Blocker of HCN Channels, on the Amplitude and Gating of Both Hyperpolarization-Activated Cation and Delayed-Rectifier Potassium Currents |
| title_sort | inhibitory effective perturbations of cilobradine dk ah269 a blocker of hcn channels on the amplitude and gating of both hyperpolarization activated cation and delayed rectifier potassium currents |
| topic | cilobradine hyperpolarization-activated cation current delayed-rectifier K<sup>+</sup> current impedance magnitude analysis current kinetics pituitary cell |
| url | https://www.mdpi.com/1422-0067/21/7/2416 |
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