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High Effectiveness in Actions of Carfilzomib on Delayed-Rectifier K+ Current and on Spontaneous Action Potentials
Edmund Cheung So1,2, Ping-Yen Liu3, Chien-Ching Lee1,4
1Department of Anesthesia, An Nan Hospital, China Medical University, Tainan, Taiwan.
Abstract:
Carfilzomib (CFZ, Kyprolis®) is widely recognized as an irreversible inhibitor of proteasome activity; however, its actions on ion currents in electrically excitable cells are largely unresolved. The possible actions of CFZ on ionic currents and membrane potential in pituitary GH3, A7r5 vascular smooth muscle, and heart-derived H9c2 cells were extensively investigated in this study. The presence of CFZ suppressed the amplitude of delayed-rectifier K+ current (I K(DR)) in a time-, state-, and concentration-dependent manner in pituitary GH3 cells. Based on minimal reaction scheme, the value of dissociation constant for CFZ-induced open-channel block of I K(DR) in these cells was 0.33 µM, which is similar to the IC50 value (0.32 µM) used for its efficacy on inhibition of I K(DR) amplitude. Recovery from I K(DR) block by CFZ (0.3 µM and 1 µM) could be well fitted by single exponential with 447 and 645 ms, respectively. The M-type K+ current, another type of K+ current elicited by low-threshold potential, was slightly suppressed by CFZ (1 µM). Under current-clamp condition, addition of CFZ depolarized GH3 cells, broadened the duration of action potentials as well as raised the firing frequency. In A7r5 vascular smooth muscle cells or H9c2 cardiac cells, the CFZ-induced inhibition of I K(DR) remained efficacious. Therefore, our study led us to reflect that CFZ or other structurally similar compounds should somehow act on the activity of membrane KV channels through which they influence the functional activities in different types of electrically excitable cells such as endocrine, neuroendocrine cells, smooth muscle cells, or heart cells, if similar in vivo findings occur.
Insights
Carfilzomib, a proteasome inhibitor, affects ion currents in electrically active cells. This study reveals carfilzomib suppresses potassium currents and alters cell electrical activity, suggesting potential impacts on various cell types.
Area of Science:
- Electrophysiology
- Pharmacology
- Cell Biology
Background:
- Carfilzomib (CFZ) is a proteasome inhibitor with largely unknown effects on ion currents in excitable cells.
- Understanding CFZ's impact on ion channels is crucial for evaluating its broader physiological effects.
Purpose of the Study:
- To investigate the actions of carfilzomib on ionic currents and membrane potential in pituitary GH3, A7r5 vascular smooth muscle, and H9c2 cardiac cells.
- To elucidate the mechanism of CFZ's interaction with potassium currents.
Main Methods:
- Whole-cell patch-clamp electrophysiology was used to measure ionic currents (delayed-rectifier K+, I K(DR), and M-type K+) and membrane potential.
- Concentration-response, time-course, and recovery experiments were performed to characterize CFZ's effects.
- Data analysis included fitting to kinetic schemes and IC50 calculations.
Main Results:
- Carfilzomib significantly suppressed delayed-rectifier K+ current (I K(DR)) in GH3 cells in a time-, state-, and concentration-dependent manner, with a dissociation constant of 0.33 µM.
- CFZ also slightly inhibited M-type K+ current and, under current-clamp, depolarized GH3 cells, broadened action potentials, and increased firing frequency.
- Similar inhibition of I K(DR) by CFZ was observed in A7r5 vascular smooth muscle and H9c2 cardiac cells.
Conclusions:
- Carfilzomib acts as an open-channel blocker of delayed-rectifier K+ channels.
- CFZ influences the electrical activity of various excitable cells, including endocrine, neuroendocrine, smooth muscle, and cardiac cells, by modulating K+ channel function.
- These findings suggest that carfilzomib and related compounds may have broader implications for cellular function beyond proteasome inhibition.
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