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External Hemin as an Inhibitor of Mitochondrial Large-Conductance Calcium-Activated Potassium Channel Activity. Int J Mol Sci 2022; 23:ijms232113391. [DOI: 10.3390/ijms232113391] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2022] [Revised: 10/26/2022] [Accepted: 11/01/2022] [Indexed: 11/06/2022] Open
Abstract
The mitochondrial large-conductance calcium-activated potassium channel (mitoBKCa) is located in the inner mitochondrial membrane and seems to play a crucial role in cytoprotection. The mitoBKCa channel is regulated by many modulators, including activators, such as calcium ions and inhibitors, such as heme and its oxidized form hemin. Heme/hemin binds to the heme-binding motif (CXXCH) located between two RCK domains present in the mitochondrial matrix. In the present study, we used the patch-clamp technique in the outside-out configuration to record the activity of mitoBKCa channels. This allowed for the application of channel modulators to the intermembrane-space side of the mitoBKCa. We found that hemin applied in this configuration inhibits the activity of mitoBKCa. In addition, we proved that the observed hemin effect is specific and it is not due to its interaction with the inner mitochondrial membrane. Our data suggest the existence of a new potential heme/hemin binding site in the structure of the mitoBKCa channel located on the mitochondrial intermembrane space side, which could constitute a new way for the regulation of mitoBKCa channel activity.
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Kampa RP, Flori L, Sęk A, Spezzini J, Brogi S, Szewczyk A, Calderone V, Bednarczyk P, Testai L. Luteolin-Induced Activation of Mitochondrial BK Ca Channels: Undisclosed Mechanism of Cytoprotection. Antioxidants (Basel) 2022; 11:1892. [PMID: 36290615 PMCID: PMC9598376 DOI: 10.3390/antiox11101892] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2022] [Revised: 09/20/2022] [Accepted: 09/21/2022] [Indexed: 09/29/2023] Open
Abstract
Luteolin (LUT) is a well-known flavonoid that exhibits a number of beneficial properties. Among these, it shows cardioprotective effects, as confirmed by numerous studies. However, its effect on mitochondrial potassium channels, the activation of which is related to cytoprotection, as well as on heart ischemia/reperfusion (I/R) damage prevention, has not yet been investigated. The large conductance calcium-regulated potassium channel (mitoBKCa) has been identified in both the mitochondria of the vascular endothelial cells, which plays a significant role in the functioning of the cardiovascular system under oxidative stress-related conditions, and in the mitochondria of cardiomyocytes, where it is deeply involved in cardiac protection against I/R injury. Therefore, the aim of this study was to explore the role of the mitoBKCa channel in luteolin-induced cytoprotection. A number of in vitro, in vivo, ex vivo and in silico studies have confirmed that luteolin activates this channel in the mitochondria of cardiomyocytes and endothelial cells, which in turn leads to the protection of the endothelium and a significant reduction in the extent of damage resulting from myocardial infarction, where this effect was partially abolished by the mitoBKCa channel blocker paxilline. In conclusion, these results suggest that luteolin has cardioprotective effects, at least in part, through the activation of the mitoBKCa channel, shedding light on a new putative mechanism of action.
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Affiliation(s)
- Rafał P. Kampa
- Laboratory of Intracellular Ion Channels, Nencki Institute of Experimental Biology PAS, 02-093 Warsaw, Poland
- Department of Pharmacology, Faculty of Pharmacy, University of Pisa, 6 via Bonanno Pisano, 56120 Pisa, Italy
| | - Lorenzo Flori
- Department of Pharmacology, Faculty of Pharmacy, University of Pisa, 6 via Bonanno Pisano, 56120 Pisa, Italy
| | - Aleksandra Sęk
- Laboratory of Intracellular Ion Channels, Nencki Institute of Experimental Biology PAS, 02-093 Warsaw, Poland
| | - Jacopo Spezzini
- Department of Pharmacology, Faculty of Pharmacy, University of Pisa, 6 via Bonanno Pisano, 56120 Pisa, Italy
| | - Simone Brogi
- Department of Pharmacology, Faculty of Pharmacy, University of Pisa, 6 via Bonanno Pisano, 56120 Pisa, Italy
| | - Adam Szewczyk
- Laboratory of Intracellular Ion Channels, Nencki Institute of Experimental Biology PAS, 02-093 Warsaw, Poland
| | - Vincenzo Calderone
- Department of Pharmacology, Faculty of Pharmacy, University of Pisa, 6 via Bonanno Pisano, 56120 Pisa, Italy
| | - Piotr Bednarczyk
- Department of Physics and Biophysics, Institute of Biology, Warsaw University of Life Sciences–SGGW (WULS-SGGW), 159 Nowoursynowska St., 02-776 Warsaw, Poland
| | - Lara Testai
- Department of Pharmacology, Faculty of Pharmacy, University of Pisa, 6 via Bonanno Pisano, 56120 Pisa, Italy
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Boengler K, Leybaert L, Ruiz-Meana M, Schulz R. Connexin 43 in Mitochondria: What Do We Really Know About Its Function? Front Physiol 2022; 13:928934. [PMID: 35860665 PMCID: PMC9289461 DOI: 10.3389/fphys.2022.928934] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2022] [Accepted: 05/26/2022] [Indexed: 01/04/2023] Open
Abstract
Connexins are known for their ability to mediate cell-cell communication via gap junctions and also form hemichannels that pass ions and molecules over the plasma membrane when open. Connexins have also been detected within mitochondria, with mitochondrial connexin 43 (Cx43) being the best studied to date. In this review, we discuss evidence for Cx43 presence in mitochondria of cell lines, primary cells and organs and summarize data on its localization, import and phosphorylation status. We further highlight the influence of Cx43 on mitochondrial function in terms of respiration, opening of the mitochondrial permeability transition pore and formation of reactive oxygen species, and also address the presence of a truncated form of Cx43 termed Gja1-20k. Finally, the role of mitochondrial Cx43 in pathological conditions, particularly in the heart, is discussed.
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Affiliation(s)
- Kerstin Boengler
- Institute of Physiology, Justus-Liebig University, Giessen, Germany
| | - Luc Leybaert
- Department of Basic and Applied Medical Sciences—Physiology Group, Faculty of Medicine and Health Sciences, Ghent University, Ghent, Belgium
| | - Marisol Ruiz-Meana
- Cardiovascular Diseases Research Group, Vall d’Hebron Institut de Recerca (VHIR), Vall d’Hebron Hospital Universitari, Barcelona, Spain
| | - Rainer Schulz
- Institute of Physiology, Justus-Liebig University, Giessen, Germany
- *Correspondence: Rainer Schulz,
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Walewska A, Szewczyk A, Krajewska M, Koprowski P. Targeting mitochondrial large-conductance calcium-activated potassium channel by hydrogen sulfide via heme-binding site. J Pharmacol Exp Ther 2022; 381:137-150. [DOI: 10.1124/jpet.121.001017] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2021] [Accepted: 02/10/2022] [Indexed: 11/22/2022] Open
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Methods of Measuring Mitochondrial Potassium Channels: A Critical Assessment. Int J Mol Sci 2022; 23:ijms23031210. [PMID: 35163132 PMCID: PMC8835872 DOI: 10.3390/ijms23031210] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2021] [Revised: 01/19/2022] [Accepted: 01/20/2022] [Indexed: 12/22/2022] Open
Abstract
In this paper, the techniques used to study the function of mitochondrial potassium channels are critically reviewed. The majority of these techniques have been known for many years as a result of research on plasma membrane ion channels. Hence, in this review, we focus on the critical evaluation of techniques used in the studies of mitochondrial potassium channels, describing their advantages and limitations. Functional analysis of mitochondrial potassium channels in comparison to that of plasmalemmal channels presents additional experimental challenges. The reliability of functional studies of mitochondrial potassium channels is often affected by the need to isolate mitochondria and by functional properties of mitochondria such as respiration, metabolic activity, swelling capacity, or high electrical potential. Three types of techniques are critically evaluated: electrophysiological techniques, potassium flux measurements, and biochemical techniques related to potassium flux measurements. Finally, new possible approaches to the study of the function of mitochondrial potassium channels are presented. We hope that this review will assist researchers in selecting reliable methods for studying, e.g., the effects of drugs on mitochondrial potassium channel function. Additionally, this review should aid in the critical evaluation of the results reported in various articles on mitochondrial potassium channels.
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Olszewska AM, Sieradzan AK, Bednarczyk P, Szewczyk A, Żmijewski MA. Mitochondrial potassium channels: A novel calcitriol target. Cell Mol Biol Lett 2022; 27:3. [PMID: 34979905 PMCID: PMC8903690 DOI: 10.1186/s11658-021-00299-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2021] [Accepted: 12/20/2021] [Indexed: 02/07/2023] Open
Abstract
BACKGROUND Calcitriol (an active metabolite of vitamin D) modulates the expression of hundreds of human genes by activation of the vitamin D nuclear receptor (VDR). However, VDR-mediated transcriptional modulation does not fully explain various phenotypic effects of calcitriol. Recently a fast non-genomic response to vitamin D has been described, and it seems that mitochondria are one of the targets of calcitriol. These non-classical calcitriol targets open up a new area of research with potential clinical applications. The goal of our study was to ascertain whether calcitriol can modulate mitochondrial function through regulation of the potassium channels present in the inner mitochondrial membrane. METHODS The effects of calcitriol on the potassium ion current were measured using the patch-clamp method modified for the inner mitochondrial membrane. Molecular docking experiments were conducted in the Autodock4 program. Additionally, changes in gene expression were investigated by qPCR, and transcription factor binding sites were analyzed in the CiiiDER program. RESULTS For the first time, our results indicate that calcitriol directly affects the activity of the mitochondrial large-conductance Ca2+-regulated potassium channel (mitoBKCa) from the human astrocytoma (U-87 MG) cell line but not the mitochondrial calcium-independent two-pore domain potassium channel (mitoTASK-3) from human keratinocytes (HaCaT). The open probability of the mitoBKCa channel in high calcium conditions decreased after calcitriol treatment and the opposite effect was observed in low calcium conditions. Moreover, using the AutoDock4 program we predicted the binding poses of calcitriol to the calcium-bound BKCa channel and identified amino acids interacting with the calcitriol molecule. Additionally, we found that calcitriol influences the expression of genes encoding potassium channels. Such a dual, genomic and non-genomic action explains the pleiotropic activity of calcitriol. CONCLUSIONS Calcitriol can regulate the mitochondrial large-conductance calcium-regulated potassium channel. Our data open a new chapter in the study of non-genomic responses to vitamin D with potential implications for mitochondrial bioenergetics and cytoprotective mechanisms.
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Affiliation(s)
- Anna M Olszewska
- Department of Histology, Medical University of Gdańsk, 1a Dębinki, 80-211, Gdańsk, Poland
| | - Adam K Sieradzan
- Faculty of Chemistry, University of Gdańsk, Wita Stwosza 63, 80-308, Gdańsk, Poland
| | - Piotr Bednarczyk
- Department of Physics and Biophysics, Warsaw University of Life Sciences-SGGW, Nowoursynowska 159, 02-776, Warsaw, Poland
| | - Adam Szewczyk
- Laboratory of Intracellular Ion Channels, Nencki Institute of Experimental Biology, Polish Academy of Sciences, 02-093, Warsaw, Poland
| | - Michał A Żmijewski
- Department of Histology, Medical University of Gdańsk, 1a Dębinki, 80-211, Gdańsk, Poland.
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Kravenska Y, Checchetto V, Szabo I. Routes for Potassium Ions across Mitochondrial Membranes: A Biophysical Point of View with Special Focus on the ATP-Sensitive K + Channel. Biomolecules 2021; 11:1172. [PMID: 34439838 PMCID: PMC8393992 DOI: 10.3390/biom11081172] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Revised: 07/29/2021] [Accepted: 08/02/2021] [Indexed: 12/18/2022] Open
Abstract
Potassium ions can cross both the outer and inner mitochondrial membranes by means of multiple routes. A few potassium-permeable ion channels exist in the outer membrane, while in the inner membrane, a multitude of different potassium-selective and potassium-permeable channels mediate K+ uptake into energized mitochondria. In contrast, potassium is exported from the matrix thanks to an H+/K+ exchanger whose molecular identity is still debated. Among the K+ channels of the inner mitochondrial membrane, the most widely studied is the ATP-dependent potassium channel, whose pharmacological activation protects cells against ischemic damage and neuronal injury. In this review, we briefly summarize and compare the different hypotheses regarding the molecular identity of this patho-physiologically relevant channel, taking into account the electrophysiological characteristics of the proposed components. In addition, we discuss the characteristics of the other channels sharing localization to both the plasma membrane and mitochondria.
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Affiliation(s)
| | | | - Ildiko Szabo
- Department of Biology, University of Padova, 35131 Padova, Italy; (Y.K.); (V.C.)
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