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Davis MJ, Earley S, Li YS, Chien S. Vascular mechanotransduction. Physiol Rev 2023; 103:1247-1421. [PMID: 36603156 PMCID: PMC9942936 DOI: 10.1152/physrev.00053.2021] [Citation(s) in RCA: 50] [Impact Index Per Article: 50.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2021] [Revised: 09/26/2022] [Accepted: 10/04/2022] [Indexed: 01/07/2023] Open
Abstract
This review aims to survey the current state of mechanotransduction in vascular smooth muscle cells (VSMCs) and endothelial cells (ECs), including their sensing of mechanical stimuli and transduction of mechanical signals that result in the acute functional modulation and longer-term transcriptomic and epigenetic regulation of blood vessels. The mechanosensors discussed include ion channels, plasma membrane-associated structures and receptors, and junction proteins. The mechanosignaling pathways presented include the cytoskeleton, integrins, extracellular matrix, and intracellular signaling molecules. These are followed by discussions on mechanical regulation of transcriptome and epigenetics, relevance of mechanotransduction to health and disease, and interactions between VSMCs and ECs. Throughout this review, we offer suggestions for specific topics that require further understanding. In the closing section on conclusions and perspectives, we summarize what is known and point out the need to treat the vasculature as a system, including not only VSMCs and ECs but also the extracellular matrix and other types of cells such as resident macrophages and pericytes, so that we can fully understand the physiology and pathophysiology of the blood vessel as a whole, thus enhancing the comprehension, diagnosis, treatment, and prevention of vascular diseases.
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Affiliation(s)
- Michael J Davis
- Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri
| | - Scott Earley
- Department of Pharmacology, University of Nevada, Reno, Nevada
| | - Yi-Shuan Li
- Department of Bioengineering, University of California, San Diego, California
- Institute of Engineering in Medicine, University of California, San Diego, California
| | - Shu Chien
- Department of Bioengineering, University of California, San Diego, California
- Institute of Engineering in Medicine, University of California, San Diego, California
- Department of Medicine, University of California, San Diego, California
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2
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Vera OD, Wulff H, Braun AP. Endothelial KCa channels: Novel targets to reduce atherosclerosis-driven vascular dysfunction. Front Pharmacol 2023; 14:1151244. [PMID: 37063294 PMCID: PMC10102451 DOI: 10.3389/fphar.2023.1151244] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2023] [Accepted: 03/24/2023] [Indexed: 04/03/2023] Open
Abstract
Elevated levels of cholesterol in the blood can induce endothelial dysfunction, a condition characterized by impaired nitric oxide production and decreased vasodilatory capacity. Endothelial dysfunction can promote vascular disease, such as atherosclerosis, where macrophages accumulate in the vascular intima and fatty plaques form that impair normal blood flow in conduit arteries. Current pharmacological strategies to treat atherosclerosis mostly focus on lipid lowering to prevent high levels of plasma cholesterol that induce endothelial dysfunction and atherosclerosis. While this approach is effective for most patients with atherosclerosis, for some, lipid lowering is not enough to reduce their cardiovascular risk factors associated with atherosclerosis (e.g., hypertension, cardiac dysfunction, stroke, etc.). For such patients, additional strategies targeted at reducing endothelial dysfunction may be beneficial. One novel strategy to restore endothelial function and mitigate atherosclerosis risk is to enhance the activity of Ca2+-activated K+ (KCa) channels in the endothelium with positive gating modulator drugs. Here, we review the mechanism of action of these small molecules and discuss their ability to improve endothelial function. We then explore how this strategy could mitigate endothelial dysfunction in the context of atherosclerosis by examining how KCa modulators can improve cardiovascular function in other settings, such as aging and type 2 diabetes. Finally, we consider questions that will need to be addressed to determine whether KCa channel activation could be used as a long-term add-on to lipid lowering to augment atherosclerosis treatment, particularly in patients where lipid-lowering is not adequate to improve their cardiovascular health.
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Affiliation(s)
- O. Daniel Vera
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada
| | - Heike Wulff
- Department of Pharmacology, School of Medicine, University of California, Davis, CA, United States
| | - Andrew P. Braun
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada
- *Correspondence: Andrew P. Braun,
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3
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Sancho M, Klug NR, Mughal A, Koide M, Huerta de la Cruz S, Heppner TJ, Bonev AD, Hill-Eubanks D, Nelson MT. Adenosine signaling activates ATP-sensitive K + channels in endothelial cells and pericytes in CNS capillaries. Sci Signal 2022; 15:eabl5405. [PMID: 35349300 DOI: 10.1126/scisignal.abl5405] [Citation(s) in RCA: 29] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
The dense network of capillaries composed of capillary endothelial cells (cECs) and pericytes lies in close proximity to all neurons, ideally positioning it to sense neuron- and glial-derived compounds that enhance regional and global cerebral perfusion. The membrane potential (VM) of vascular cells serves as the physiological bridge that translates brain activity into vascular function. In other beds, the ATP-sensitive K+ (KATP) channel regulates VM in vascular smooth muscle, which is absent in the capillary network. Here, with transgenic mice that expressed a dominant-negative mutant of the pore-forming Kir6.1 subunit specifically in brain cECs or pericytes, we demonstrated that KATP channels were present in both cell types and robustly controlled VM. We further showed that the signaling nucleotide adenosine acted through A2A receptors and the Gαs/cAMP/PKA pathway to activate capillary KATP channels. Moreover, KATP channel stimulation in vivo increased cerebral blood flow (CBF), an effect that was blunted by expression of the dominant-negative Kir6.1 mutant in either capillary cell type. These findings establish an important role for KATP channels in cECs and pericytes in the regulation of CBF.
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Affiliation(s)
- Maria Sancho
- Department of Pharmacology, University of Vermont, Burlington, VT 05405-0068, USA
| | - Nicholas R Klug
- Department of Pharmacology, University of Vermont, Burlington, VT 05405-0068, USA
| | - Amreen Mughal
- Department of Pharmacology, University of Vermont, Burlington, VT 05405-0068, USA
| | - Masayo Koide
- Department of Pharmacology, University of Vermont, Burlington, VT 05405-0068, USA.,Vermont Center for Cardiovascular and Brain Health, Larner College of Medicine, University of Vermont, Burlington, VT 05405-0068, USA
| | | | - Thomas J Heppner
- Department of Pharmacology, University of Vermont, Burlington, VT 05405-0068, USA
| | - Adrian D Bonev
- Department of Pharmacology, University of Vermont, Burlington, VT 05405-0068, USA
| | - David Hill-Eubanks
- Department of Pharmacology, University of Vermont, Burlington, VT 05405-0068, USA
| | - Mark T Nelson
- Department of Pharmacology, University of Vermont, Burlington, VT 05405-0068, USA.,Vermont Center for Cardiovascular and Brain Health, Larner College of Medicine, University of Vermont, Burlington, VT 05405-0068, USA.,Division of Cardiovascular Sciences, University of Manchester, Manchester M13 9PL, UK
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4
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Kendrick DJ, Mishra RC, John CM, Zhu HL, Braun AP. Effects of Pharmacological Inhibitors of NADPH Oxidase on Myogenic Contractility and Evoked Vasoactive Responses in Rat Resistance Arteries. Front Physiol 2022; 12:752366. [PMID: 35140625 PMCID: PMC8818784 DOI: 10.3389/fphys.2021.752366] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2021] [Accepted: 12/17/2021] [Indexed: 11/17/2022] Open
Abstract
Reactive oxygen species (ROS), such as superoxide anions and hydrogen peroxide, are reported to contribute to the dynamic regulation of contractility in various arterial preparations, however, the situation in pressurized, myogenically active resistance arteries is much less clear. In the present study, we have utilized established pharmacological inhibitors of NADPH oxidase activity to examine the potential contribution of ROS to intrinsic myogenic contractility in adult Sprague–Dawley rat resistance arteries and responses to vasoactive agents acting via the endothelium (i.e., acetylcholine, SKA-31) or smooth muscle (i.e., sodium nitroprusside, phenylephrine). In cannulated and pressurized cremaster skeletal muscle and middle cerebral arteries, the NOX inhibitors 2-acetylphenothiazine (2-APT) and VAS2870, selective for NOX1 and NOX2, respectively, evoked concentration-dependent inhibition of basal myogenic tone in a reversible and irreversible manner, respectively, whereas the non-selective inhibitor apocynin augmented myogenic contractility. The vasodilatory actions of 2-APT and VAS2870 occurred primarily via the vascular endothelium and smooth muscle, respectively. Functional responses to established endothelium-dependent and –independent vasoactive agents were largely unaltered in the presence of either 2-APT or apocynin. In cremaster arteries from Type 2 Diabetic (T2D) Goto-Kakizaki rats with endothelial dysfunction, treatment with either 2-APT or apocynin did not modify stimulus-evoked vasoactive responses, but did affect basal myogenic tone. These same NOX inhibitors produced robust inhibition of total NADPH oxidase activity in aortic tissue homogenates from control and T2D rats, and NOX isozymes 1, 2 and 4, along with superoxide dismutase 1, were detected by qPCR in cremaster arteries and aorta from both species. Based on the diverse effects that we observed for established, chemically distinct NOX inhibitors, the functional contribution of vascular NADPH oxidase activity to stimulus-evoked vasoactive signaling in myogenically active, small resistance arteries remains unclear.
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5
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Hakim MA, Behringer EJ. Development of Alzheimer's Disease Progressively Alters Sex-Dependent KCa and Sex-Independent KIR Channel Function in Cerebrovascular Endothelium. J Alzheimers Dis 2021; 76:1423-1442. [PMID: 32651315 DOI: 10.3233/jad-200085] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
BACKGROUND Development of Alzheimer's disease (AD) pathology is associated with impaired blood flow delivery of oxygen and nutrients throughout the brain. Cerebrovascular endothelium regulates vasoreactivity of blood vessel networks for optimal cerebral blood flow. OBJECTIVE We tested the hypothesis that cerebrovascular endothelial Gq-protein-coupled receptor (GPCR; purinergic and muscarinic) and K+ channel [Ca2+-activated (KCa2.3/SK3 and KCa3.1/IK1) and inward-rectifying (KIR2.x)] function declines during progressive AD pathology. METHODS We applied simultaneous measurements of intracellular Ca2+ ([Ca2+]i) and membrane potential (Vm) in freshly isolated endothelium from posterior cerebral arteries of 3×Tg-AD mice [young, no pathology (1- 2 mo), cognitive impairment (CI; 4- 5 mo), extracellular Aβ plaques (Aβ; 6- 8 mo), and Aβ plaques + neurofibrillary tangles (AβT; 12- 15 mo)]. RESULTS The coupling of ΔVm-to-Δ[Ca2+]i during AβT pathology was lowest for both sexes but, overall, ATP-induced purinergic receptor function was stable throughout AD pathology. SKCa/IKCa channel function itself was enhanced by ∼20% during AD (Aβ+ AβT) versus pre-AD (Young + CI) in males while steady in females. Accordingly, hyperpolarization-induced [Ca2+]i increases following SKCa/IKCa channel activation and Δ[Ca2+]i-to-ΔVm coupling was enhanced by ≥two-fold during AD pathology in males but not females. Further, KIR channel function decreased by ∼50% during AD conditions versus young regardless of sex. Finally, other than a ∼40% increase in females versus males during Aβ pathology, [Ca2+]i responses to the mitochondrial uncoupler FCCP were similar among AD versus pre-AD conditions. CONCLUSION Altogether, AD pathology represents a condition of altered KCa and KIR channel function in cerebrovascular endothelium in a sex-dependent and sex-independent manner respectively.
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Affiliation(s)
- Md A Hakim
- Basic Sciences, Loma Linda University, Loma Linda, CA, USA
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6
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Mishra RC, Kyle BD, Kendrick DJ, Svystonyuk D, Kieser TM, Fedak PWM, Wulff H, Braun AP. KCa channel activation normalizes endothelial function in Type 2 Diabetic resistance arteries by improving intracellular Ca 2+ mobilization. Metabolism 2021; 114:154390. [PMID: 33039407 PMCID: PMC7736096 DOI: 10.1016/j.metabol.2020.154390] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/14/2020] [Revised: 09/28/2020] [Accepted: 09/30/2020] [Indexed: 10/23/2022]
Abstract
BACKGROUND Endothelial dysfunction is an early pathogenic event in the progression of cardiovascular disease in patients with Type 2 Diabetes (T2D). Endothelial KCa2.3 and KCa3.1 K+ channels are important regulators of arterial diameter, and we thus hypothesized that SKA-31, a small molecule activator of KCa2.3 and KCa3.1, would positively influence agonist-evoked dilation in myogenically active resistance arteries in T2D. METHODOLOGY Arterial pressure myography was utilized to investigate endothelium-dependent vasodilation in isolated cremaster skeletal muscle resistance arteries from 22 to 24 week old T2D Goto-Kakizaki rats, age-matched Wistar controls, and small human intra-thoracic resistance arteries from T2D subjects. Agonist stimulated changes in cytosolic free Ca2+ in acutely isolated, single endothelial cells from Wistar and T2D Goto-Kakizaki cremaster and cerebral arteries were examined using Fura-2 fluorescence imaging. MAIN FINDINGS Endothelium-dependent vasodilation in response to acetylcholine (ACh) or bradykinin (BK) was significantly impaired in isolated cremaster arteries from T2D Goto-Kakizaki rats compared with Wistar controls, and similar results were observed in human intra-thoracic arteries. In contrast, inhibition of myogenic tone by sodium nitroprusside, a direct smooth muscle relaxant, was unaltered in both rat and human T2D arteries. Treatment with a threshold concentration of SKA-31 (0.3 μM) significantly enhanced vasodilatory responses to ACh and BK in arteries from T2D Goto-Kakizaki rats and human subjects, whereas only modest effects were observed in non-diabetic arteries of both species. Mechanistically, SKA-31 enhancement of evoked dilation was independent of vascular NO synthase and COX activities. Remarkably, SKA-31 treatment improved agonist-stimulated Ca2+ elevation in acutely isolated endothelial cells from T2D Goto-Kakizaki cremaster and cerebral arteries, but not from Wistar control vessels. In contrast, SKA-31 treatment did not affect intracellular Ca2+ release by the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) inhibitor cyclopiazonic acid. CONCLUSIONS Collectively, our data demonstrate that KCa channel modulation can acutely restore endothelium-dependent vasodilatory responses in T2D resistance arteries from rats and humans, which appears to involve improved endothelial Ca2+ mobilization.
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Affiliation(s)
- Ramesh C Mishra
- Dept. of Physiology and Pharmacology, Libin Cardiovascular Institute of Alberta, University of Calgary, 3330 Hospital Drive NW, Calgary, AB T2N 4N1, Canada
| | - Barry D Kyle
- Dept. of Physiology and Pharmacology, Libin Cardiovascular Institute of Alberta, University of Calgary, 3330 Hospital Drive NW, Calgary, AB T2N 4N1, Canada
| | - Dylan J Kendrick
- Dept. of Physiology and Pharmacology, Libin Cardiovascular Institute of Alberta, University of Calgary, 3330 Hospital Drive NW, Calgary, AB T2N 4N1, Canada
| | - Daniyil Svystonyuk
- Dept. of Cardiac Sciences, Libin Cardiovascular Institute of Alberta, University of Calgary, 3330 Hospital Drive NW, Calgary, AB T2N 4N1, Canada
| | - Teresa M Kieser
- Dept. of Cardiac Sciences, Libin Cardiovascular Institute of Alberta, University of Calgary, 3330 Hospital Drive NW, Calgary, AB T2N 4N1, Canada
| | - Paul W M Fedak
- Dept. of Cardiac Sciences, Libin Cardiovascular Institute of Alberta, University of Calgary, 3330 Hospital Drive NW, Calgary, AB T2N 4N1, Canada
| | - Heike Wulff
- Dept of Pharmacology, University of California Davis, 451 Health Sciences Drive, Davis, CA 95616, USA
| | - Andrew P Braun
- Dept. of Physiology and Pharmacology, Libin Cardiovascular Institute of Alberta, University of Calgary, 3330 Hospital Drive NW, Calgary, AB T2N 4N1, Canada.
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7
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John CM, Khaddaj Mallat R, Mishra RC, George G, Singh V, Turnbull JD, Umeshappa CS, Kendrick DJ, Kim T, Fauzi FM, Visser F, Fedak PWM, Wulff H, Braun AP. SKA-31, an activator of Ca 2+-activated K + channels, improves cardiovascular function in aging. Pharmacol Res 2019; 151:104539. [PMID: 31707036 DOI: 10.1016/j.phrs.2019.104539] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/25/2019] [Revised: 10/22/2019] [Accepted: 11/06/2019] [Indexed: 12/16/2022]
Abstract
Aging represents an independent risk factor for the development of cardiovascular disease, and is associated with complex structural and functional alterations in the vasculature, such as endothelial dysfunction. Small- and intermediate-conductance, Ca2+-activated K+ channels (KCa2.3 and KCa3.1, respectively) are prominently expressed in the vascular endothelium, and pharmacological activators of these channels induce robust vasodilation upon acute exposure in isolated arteries and intact animals. However, the effects of prolonged in vivo administration of such compounds are unknown. In our study, we hypothesized that such treatment would ameliorate aging-related cardiovascular deficits. Aged (∼18 months) male Sprague Dawley rats were treated daily with either vehicle or the KCa channel activator SKA-31 (10 mg/kg, intraperitoneal injection; n = 6/group) for 8 weeks, followed by echocardiography, arterial pressure myography, immune cell and plasma cytokine characterization, and tissue histology. Our results show that SKA-31 administration improved endothelium-dependent vasodilation, reduced agonist-induced vascular contractility, and prevented the aging-associated declines in cardiac ejection fraction, stroke volume and fractional shortening, and further improved the expression of endothelial KCa channels and associated cell signalling components to levels similar to those observed in young male rats (∼5 months at end of study). SKA-31 administration did not promote pro-inflammatory changes in either T cell populations or plasma cytokines/chemokines, and we observed no overt tissue histopathology in heart, kidney, aorta, brain, liver and spleen. SKA-31 treatment in young rats had little to no effect on vascular reactivity, select protein expression, tissue histology, plasma cytokines/chemokines or immune cell properties. Collectively, these data demonstrate that administration of the KCa channel activator SKA-31 improved aging-related cardiovascular function, without adversely affecting the immune system or promoting tissue toxicity.
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Affiliation(s)
- Cini Mathew John
- Dept. of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Canada; Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Canada
| | - Rayan Khaddaj Mallat
- Dept. of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Canada; Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Canada
| | - Ramesh C Mishra
- Dept. of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Canada; Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Canada
| | - Grace George
- Dept. of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Canada; Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Canada
| | - Vikrant Singh
- Dept. of Pharmacology, University of California, Davis, USA
| | - Jeannine D Turnbull
- Dept. of Cardiac Sciences, Cumming School of Medicine, University of Calgary, Canada; Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Canada
| | - Channakeshava S Umeshappa
- Dept. of Microbiology, Immunology and Infectious Diseases, Cumming School of Medicine, University of Calgary, Canada
| | - Dylan J Kendrick
- Dept. of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Canada; Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Canada
| | - Taeyeob Kim
- Dept. of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Canada; Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Canada
| | - Fazlin M Fauzi
- Dept. of Pharmacology and Chemistry, Universiti Teknologi MARA, Malaysia
| | - Frank Visser
- Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Canada
| | - Paul W M Fedak
- Dept. of Cardiac Sciences, Cumming School of Medicine, University of Calgary, Canada; Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Canada
| | - Heike Wulff
- Dept. of Pharmacology, University of California, Davis, USA
| | - Andrew P Braun
- Dept. of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Canada; Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Canada.
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Kloza M, Baranowska-Kuczko M, Toczek M, Kusaczuk M, Sadowska O, Kasacka I, Kozłowska H. Modulation of Cardiovascular Function in Primary Hypertension in Rat by SKA-31, an Activator of KCa2.x and KCa3.1 Channels. Int J Mol Sci 2019; 20:ijms20174118. [PMID: 31450834 PMCID: PMC6747311 DOI: 10.3390/ijms20174118] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Revised: 08/17/2019] [Accepted: 08/21/2019] [Indexed: 12/11/2022] Open
Abstract
The aim of this study was to investigate the hemodynamic effects of SKA-31, an activator of the small (KCa2.x) and intermediate (KCa3.1) conductance calcium-activated potassium channels, and to evaluate its influence on endothelium-derived hyperpolarization (EDH)-KCa2.3/KCa3.1 type relaxation in isolated endothelium-intact small mesenteric arteries (sMAs) from spontaneously hypertensive rats (SHRs). Functional in vivo and in vitro experiments were performed on SHRs or their normotensive controls, Wistar-Kyoto rats (WKY). SKA-31 (1, 3 and 10 mg/kg) caused a brief decrease in blood pressure and bradycardia in both SHR and WKY rats. In phenylephrine-pre-constricted sMAs of SHRs, SKA-31 (0.01–10 µM)-mediated relaxation was reduced and SKA-31 potentiated acetylcholine-evoked endothelium-dependent relaxation. Endothelium denudation and inhibition of nitric oxide synthase (eNOS) and cyclooxygenase (COX) by the respective inhibitors l-NAME or indomethacin, attenuated SKA-31-mediated vasorelaxation. The inhibition of KCa3.1, KCa2.3, KIR and Na+/K+-ATPase by TRAM-34, UCL1684, Ba2+ and ouabain, respectively, reduced the potency and efficacy of the EDH-response evoked by SKA-31. The mRNA expression of eNOS, prostacyclin synthase, KCa2.3, KCa3.1 and KIR were decreased, while Na+/K+-ATPase expression was increased. Collectively, SKA-31 promoted hypotension and vasodilatation, potentiated agonist-stimulated vasodilation, and maintained KCa2.3/KCa3.1-EDH-response in sMAs of SHR with downstream signaling that involved KIR and Na+/K+-ATPase channels. In view of the importance of the dysfunction of endothelium-mediated vasodilatation in the mechanism of hypertension, application of activators of KCa2.3/KCa3.1 channels such as SKA-31 seem to be a promising avenue in pharmacotherapy of hypertension.
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Affiliation(s)
- Monika Kloza
- Department of Experimental Physiology and Pathophysiology, Medical University of Białystok, 15-222 Białystok, Poland
| | - Marta Baranowska-Kuczko
- Department of Experimental Physiology and Pathophysiology, Medical University of Białystok, 15-222 Białystok, Poland
- Department of Clinical Pharmacy, Medical University of Białystok, 15-222 Białystok, Poland
| | - Marek Toczek
- Department of Experimental Physiology and Pathophysiology, Medical University of Białystok, 15-222 Białystok, Poland
| | - Magdalena Kusaczuk
- Department of Pharmaceutical Biochemistry, Medical University of Białystok, 15-222 Białystok, Poland
| | - Olga Sadowska
- Department of Experimental Physiology and Pathophysiology, Medical University of Białystok, 15-222 Białystok, Poland
| | - Irena Kasacka
- Department of Histology and Cytophysiology, Medical University of Białystok, 15-222 Białystok, Poland
| | - Hanna Kozłowska
- Department of Experimental Physiology and Pathophysiology, Medical University of Białystok, 15-222 Białystok, Poland.
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Khaddaj Mallat R, Mathew John C, Mishra RC, Kendrick DJ, Braun AP. Pharmacological Targeting of KCa Channels to Improve Endothelial Function in the Spontaneously Hypertensive Rat. Int J Mol Sci 2019; 20:ijms20143481. [PMID: 31315169 PMCID: PMC6678254 DOI: 10.3390/ijms20143481] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2019] [Revised: 07/05/2019] [Accepted: 07/12/2019] [Indexed: 01/01/2023] Open
Abstract
Systemic hypertension is a major risk factor for the development of cardiovascular disease and is often associated with endothelial dysfunction. KCa2.3 and KCa3.1 channels are expressed in the vascular endothelium and contribute to stimulus-evoked vasodilation. We hypothesized that acute treatment with SKA-31, a selective activator of KCa2.x and KCa3.1 channels, would improve endothelium-dependent vasodilation and transiently lower mean arterial pressure (MAP) in male, spontaneously hypertensive rats (SHRs). Isolated vascular preparations exhibited impaired vasodilation in response to bradykinin (i.e., endothelial dysfunction) compared with Wistar controls, which was associated with decreased bradykinin receptor expression in mesenteric arteries. In contrast, similar levels of endothelial KCa channel expression were observed, and SKA-31 evoked vasodilation was comparable in vascular preparations from both strains. Addition of a low concentration of SKA-31 (i.e., 0.2–0.3 μM) failed to augment bradykinin-induced vasodilation in arteries from SHRs. However, responses to acetylcholine were enhanced. Surprisingly, acute bolus administration of SKA-31 in vivo (30 mg/kg, i.p. injection) modestly elevated MAP compared with vehicle injection. In summary, pharmacological targeting of endothelial KCa channels in SHRs did not readily reverse endothelial dysfunction in situ, or lower MAP in vivo. SHRs thus appear to be less responsive to endothelial KCa channel activators, which may be related to their vascular pathology.
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Affiliation(s)
- Rayan Khaddaj Mallat
- Department of Physiology and Pharmacology and Libin Cardiovascular Institute of Alberta, Cumming School of Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, AB T2N 4N1, Canada
| | - Cini Mathew John
- Department of Physiology and Pharmacology and Libin Cardiovascular Institute of Alberta, Cumming School of Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, AB T2N 4N1, Canada
| | - Ramesh C Mishra
- Department of Physiology and Pharmacology and Libin Cardiovascular Institute of Alberta, Cumming School of Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, AB T2N 4N1, Canada
| | - Dylan J Kendrick
- Department of Physiology and Pharmacology and Libin Cardiovascular Institute of Alberta, Cumming School of Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, AB T2N 4N1, Canada
| | - Andrew P Braun
- Department of Physiology and Pharmacology and Libin Cardiovascular Institute of Alberta, Cumming School of Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, AB T2N 4N1, Canada.
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10
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Mishra RC, Rahman MM, Davis MJ, Wulff H, Hill MA, Braun AP. Alpha 1 -adrenergic stimulation selectively enhances endothelium-mediated vasodilation in rat cremaster arteries. Physiol Rep 2019; 6:e13703. [PMID: 29756401 PMCID: PMC5949301 DOI: 10.14814/phy2.13703] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2018] [Revised: 03/19/2018] [Accepted: 04/16/2018] [Indexed: 11/24/2022] Open
Abstract
We have systematically investigated how vascular smooth muscle α1‐adrenoceptor activation impacts endothelium‐mediated vasodilation in isolated, myogenically active, rat cremaster muscle 1A arteries. Cannulated cremaster arteries were pressurized intraluminally to 70 mmHg to induce myogenic tone, and exposed to vasoactive agents via bath superfusion at 34°C. Smooth muscle membrane potential was measured via sharp microelectrode recordings in pressurized, myogenic arteries. The α1‐adrenergic agonist phenylephrine (25–100 nmol/L) produced further constriction of myogenic arteries, but did not alter the vasorelaxant responses to acetylcholine (0.3 μmol/L), SKA‐31 (an activator of endothelial Ca2+‐dependent K+ channels) (3 μmol/L) or sodium nitroprusside (10 μmol/L). Exposure to 0.25–1 μmol/L phenylephrine or 1 μmol/L norepinephrine generated more robust constrictions, and also enhanced the vasodilations evoked by acetylcholine and SKA‐31, but not by sodium nitroprusside. In contrast, the thromboxane receptor agonist U46619 (250 nmol/L) dampened responses to all three vasodilators. Phenylephrine exposure depolarized myogenic arteries, and mimicking this effect with 4‐aminopyridine (1 mmol/L) was sufficient to augment the SKA‐31‐evoked vasodilation. Inhibition of L‐type Ca2+ channels by 1 μmol/L nifedipine decreased myogenic tone, phenylephrine‐induced constriction and prevented α1‐adrenergic enhancement of endothelium‐evoked vasodilation; these latter deficits were overcome by exposure to 3 and 10 μmol/L phenylephrine. Mechanistically, augmentation of ACh‐evoked dilation by phenylephrine was dampened by eNOS inhibition and abolished by blockade of endothelial KCa channels. Collectively, these data suggest that increasing α1‐adrenoceptor activation beyond a threshold level augments endothelium‐evoked vasodilation, likely by triggering transcellular signaling between smooth muscle and the endothelium. Physiologically, this negative feedback process may serve as a “brake” to limit the extent of vasoconstriction in the skeletal microcirculation evoked by the elevated sympathetic tone.
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Affiliation(s)
- Ramesh C Mishra
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Mohammad M Rahman
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Michael J Davis
- Dalton Cardiovascular Research Institute and Dept. of Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri
| | - Heike Wulff
- Department of Pharmacology, University of California Davis, Davis, California
| | - Michael A Hill
- Dalton Cardiovascular Research Institute and Dept. of Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri
| | - Andrew P Braun
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
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SKA-31, an activator of endothelial Ca 2+-activated K + channels evokes robust vasodilation in rat mesenteric arteries. Eur J Pharmacol 2018; 831:60-67. [PMID: 29753043 DOI: 10.1016/j.ejphar.2018.05.006] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Revised: 05/04/2018] [Accepted: 05/08/2018] [Indexed: 12/17/2022]
Abstract
It is now well recognized that endothelial KCa2.3 and KCa3.1 channel activities contribute to dilation of resistance arteries via endothelium-mediated hyperpolarization and vascular smooth muscle relaxation. In this study, we have investigated the functional effect of the KCa channel activator SKA-31 in third order rat mesenteric arteries using arterial pressure myography. Isolated arteries were cannulated, pressurized intraluminally to 70 mmHg at 36 °C and then constricted with 1 μM phenylephrine. Acute bath exposure to SKA-31 evoked a robust and reversible inhibition of developed tone (IC50 = 0.22 μM). The vasodilatory effects of SKA-31 and acetylcholine were blunted in the presence of KCa2.3 and KCa3.1 channel antagonists, and were largely prevented following endothelial denudation. Western blot and q-PCR analyses of isolated mesenteric arteries revealed KCa2.3 and KCa3.1 channel expression at the protein and mRNA levels, respectively. Penitrem-A, an inhibitor of KCa1.1 channels, decreased vasodilatory responses to acetylcholine, sodium nitroprusside and NS-1619, but had little effect on SKA-31. Similarly, bath exposure to the eNOS inhibitor L-NAME did not alter SKA-31 and acetylcholine-mediated vasodilation. Collectively, these data highlight the major cellular mechanisms by which the endothelial KCa channel activator SKA-31 inhibits agonist-evoked vasoconstriction in rat small mesenteric arteries.
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Mathew John C, Khaddaj Mallat R, George G, Kim T, Mishra RC, Braun AP. Pharmacologic targeting of endothelial Ca 2+-activated K + channels: A strategy to improve cardiovascular function. Channels (Austin) 2018; 12:126-136. [PMID: 29577810 PMCID: PMC5972810 DOI: 10.1080/19336950.2018.1454814] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2018] [Accepted: 03/15/2018] [Indexed: 12/17/2022] Open
Abstract
Endothelial small and intermediate-conductance, Ca2+-activated K+ channels (KCa2.3 and KCa3.1, respectively) play an important role in the regulation of vascular function and systemic blood pressure. Growing evidence indicates that they are intimately involved in agonist-evoked vasodilation of small resistance arteries throughout the circulation. Small molecule activators of KCa2.x and 3.1 channels, such as SKA-31, can acutely inhibit myogenic tone in isolated resistance arteries, induce effective vasodilation in intact vascular beds, such as the coronary circulation, and acutely decrease systemic blood pressure in vivo. The blood pressure-lowering effect of SKA-31, and early indications of improvement in endothelial dysfunction suggest that endothelial KCa channel activators could eventually be developed into a new class of endothelial targeted agents to combat hypertension or atherosclerosis. This review summarises recent insights into the activation of endothelial Ca2+ activated K+ channels in various vascular beds, and how tools, such as SKA-31, may be beneficial in disease-related conditions.
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Affiliation(s)
- Cini Mathew John
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Rayan Khaddaj Mallat
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Grace George
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Taeyeob Kim
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Ramesh C. Mishra
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Andrew P. Braun
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
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Lukaszewicz KM, Durand MJ, Priestley JRC, Schmidt JR, Allen LA, Geurts AM, Lombard JH. Evaluation of Vascular Control Mechanisms Utilizing Video Microscopy of Isolated Resistance Arteries of Rats. J Vis Exp 2017. [PMID: 29286398 DOI: 10.3791/56133] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
This protocol describes the use of in vitro television microscopy to evaluate vascular function in isolated cerebral resistance arteries (and other vessels), and describes techniques for evaluating tissue perfusion using Laser Doppler Flowmetry (LDF) and microvessel density utilizing fluorescently labeled Griffonia simplicifolia (GS1) lectin. Current methods for studying isolated resistance arteries at transmural pressures encountered in vivo and in the absence of parenchymal cell influences provide a critical link between in vivo studies and information gained from molecular reductionist approaches that provide limited insight into integrative responses at the whole animal level. LDF and techniques to selectively identify arterioles and capillaries with fluorescently-labeled GS1 lectin provide practical solutions to enable investigators to extend the knowledge gained from studies of isolated resistance arteries. This paper describes the application of these techniques to gain fundamental knowledge of vascular physiology and pathology in the rat as a general experimental model, and in a variety of specialized genetically engineered "designer" rat strains that can provide important insight into the influence of specific genes on important vascular phenotypes. Utilizing these valuable experimental approaches in rat strains developed by selective breeding strategies and new technologies for producing gene knockout models in the rat, will expand the rigor of scientific premises developed in knockout mouse models and extend that knowledge to a more relevant animal model, with a well understood physiological background and suitability for physiological studies because of its larger size.
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Affiliation(s)
| | | | | | - James R Schmidt
- Graduate Programs of Nurse Anesthesia, Texas Wesleyan University
| | | | - Aron M Geurts
- Department of Physiology, Medical College of Wisconsin
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Kyle BD, Mishra RC, Braun AP. The augmentation of BK channel activity by nitric oxide signaling in rat cerebral arteries involves co-localized regulatory elements. J Cereb Blood Flow Metab 2017; 37:3759-3773. [PMID: 28155571 PMCID: PMC5718322 DOI: 10.1177/0271678x17691291] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Large conductance, Ca2+-activated K+ (BK) channels control cerebrovascular tone; however, the regulatory processes influencing these channels remain poorly understood. Here, we investigate the cellular mechanisms underlying the enhancement of BK current in rat cerebral arteries by nitric oxide (NO) signaling. In isolated cerebral myocytes, BK current magnitude was reversibly increased by sodium nitroprusside (SNP, 100 μM) and sensitive to the BK channel inhibitor, penitrem-A (100 nM). Fostriecin (30 nM), a protein phosphatase type 2A (PP2A) inhibitor, significantly prolonged the SNP-induced augmentation of BK current and a similar effect was produced by sildenafil (30 nM), a phosphodiesterase 5 (PDE5) inhibitor. Using proximity ligation assay (PLA)-based co-immunostaining, BK channels were observed to co-localize with PP2A, PDE5, and cGMP-dependent protein kinase (cGKI) (spatial restriction < 40 nm); cGKI co-localization increased following SNP exposure. SNP (10 μM) reversibly inhibited myogenic tone in cannulated cerebral arteries, which was augmented by either fostriecin or sildenafil and inhibited by penitrem-A. Collectively, these data suggest that (1) cGKI, PDE5, and PP2A are compartmentalized with cerebrovascular BK channels and determine the extent of BK current augmentation by NO/cGMP signaling, and (2) the dynamic regulation of BK activity by co-localized signaling enzymes modulates NO-evoked dilation of cerebral resistance arteries.
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Affiliation(s)
- Barry D Kyle
- Department of Physiology and Pharmacology and Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Ramesh C Mishra
- Department of Physiology and Pharmacology and Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Andrew P Braun
- Department of Physiology and Pharmacology and Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
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Protective role of ACE2-Ang-(1-7)-Mas in myocardial fibrosis by downregulating K Ca3.1 channel via ERK1/2 pathway. Pflugers Arch 2016; 468:2041-2051. [PMID: 27592222 DOI: 10.1007/s00424-016-1875-9] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2016] [Revised: 08/27/2016] [Accepted: 08/29/2016] [Indexed: 01/18/2023]
Abstract
The intermediate-conductance Ca2+-activated K+ (KCa3.1) channel plays a vital role in myocardial fibrosis induced by angiotensin (Ang) II. However, as the antagonists of Ang II, the effect of angiotensin-converting enzyme 2 (ACE2)-angiotensin-(1-7)-Mas axis on KCa3.1 channel during myocardial fibrosis remains unknown. This study was designed to explore the function of KCa3.1 channel in the cardioprotective role of ACE2-Ang-(1-7)-Mas. Wild-type (WT) mice, hACE2 transgenic mice (Tg), and ACE2 deficiency mice (ACE2-/-) were administrated with Ang II by osmotic mini-pumps. As the activator of ACE2, diminazene aceturate (DIZE) inhibited increase of blood pressure, collagen deposition, and KCa3.1 protein expression in myocardium of WT mice induced by Ang II. In Tg and ACE2-/- mice, besides the elevation of blood pressure, Ang II induced transformation of cardiac fibroblast into myofibroblast and resulted in augmentation of hydroxyproline concentration and collagen deposition, as well as KCa3.1 protein expression, but the changes in ACE2-/- mice were more obvious than those in Tg mice. Mas antagonist A779 reduced blood pressure, myocardium fibrosis, and myocardium KCa3.1 protein expression by Ang II in Tg mice, but activation of KCa3.1 with SKA-31 in Tg mice promoted the pro-fibrogenic effects of Ang II. Respectively, in ACE2-/- mice, TRAM-34, the KCa3.1 blocker, and Ang-(1-7) inhibited increase of blood pressure, collagen deposition, and KCa3.1 protein expression by Ang II. Moreover, DIZE and Ang-(1-7) depressed p-ERK1/2/t-ERK increases by Ang II in WT mice, and after blockage of ERK1/2 pathway with PD98059, the KCa3.1 protein expression was reduced in WT mice. In conclusion, the present study demonstrates that ACE2-Ang-(1-7)-Mas protects the myocardium from hypertension-induced injury, which is related to its inhibiting effect on KCa3.1 channels through ERK1/2 pathway. Our results reveal that KCa3.1 channel is likely to be a critical target on the ACE2-Ang-(1-7)-Mas axis for its protective role in myocardial fibrosis and changes of KCa3.1 induced by homeostasis of ACE-Ang II-AT1 axis and ACE2-Ang-(1-7)-Mas axis may be a new therapeutic target in myocardial fibrosis.
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Mishra RC, Mitchell JR, Gibbons-Kroeker C, Wulff H, Belenkie I, Tyberg JV, Braun AP. A pharmacologic activator of endothelial KCa channels increases systemic conductance and reduces arterial pressure in an anesthetized pig model. Vascul Pharmacol 2015; 79:24-31. [PMID: 26239885 DOI: 10.1016/j.vph.2015.07.016] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2015] [Revised: 07/24/2015] [Accepted: 07/28/2015] [Indexed: 11/27/2022]
Abstract
SKA-31, an activator of endothelial KCa2.3 and KCa3.1 channels, reduces systemic blood pressure in mice and dogs, however, its effects in larger mammals are not well known. We therefore examined the hemodynamic effects of SKA-31, along with sodium nitroprusside (SNP), in anesthetized, juvenile male domestic pigs. Experimentally, continuous measurements of left ventricular (LV), aortic and inferior vena cava (IVC) pressures, along with flows in the ascending aorta, carotid artery, left anterior descending coronary artery and renal artery, were performed during acute administration of SKA-31 (0.1, 0.3, 1.0, 3.0 and 5.0mg/ml/kg) and a single dose of SNP (5.0 μg/ml/kg). SKA-31 dose-dependently reduced mean aortic pressure (mPAO), with the highest dose decreasing mPAO to a similar extent as SNP (-23 ± 3 and -28 ± 4 mmHg, respectively). IVC pressure did not change. Systemic conductance and conductance in coronary and carotid arteries increased in response to SKA-31 and SNP, but renal artery conductance was unaffected. There was no change in either LV stroke volume (SV) or heart rate (versus the preceding control) for any infusion. With no change in SV, drug-evoked decreases in LV stroke work (SW) were attributed to reductions in mPAO (SW vs. mPAO, r(2)=0.82, P<0.001). In summary, SKA-31 dose-dependently reduced mPAO by increasing systemic and arterial conductances. Primary reductions in mPAO by SKA-31 largely account for associated decreases in SW, implying that SKA-31 does not directly impair cardiac contractility.
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Affiliation(s)
- Ramesh C Mishra
- Dept. of Physiology & Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; The Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada
| | - Jamie R Mitchell
- Dept of Physiology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - Carol Gibbons-Kroeker
- Dept. of Physiology & Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Dept. of Medicine, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; The Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada; Dept. of Biology, Ambrose University College, Calgary, Alberta, Canada
| | - Heike Wulff
- Dept. of Pharmacology, University of California Davis, Davis, CA, USA
| | - Israel Belenkie
- Dept. of Cardiac Sciences, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Dept. of Medicine, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; The Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada
| | - John V Tyberg
- Dept. of Physiology & Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Dept. of Cardiac Sciences, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; The Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada
| | - Andrew P Braun
- Dept. of Physiology & Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; The Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada.
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