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Kalashnyk O, Lykhmus O, Koval L, Uspenska K, Obolenskaya M, Chernyshov V, Komisarenko S, Skok M. α7 Nicotinic acetylcholine receptors regulate translocation of HIF-1α to the cell nucleus and mitochondria upon hypoxia. Biochem Biophys Res Commun 2023; 657:35-42. [PMID: 36972659 DOI: 10.1016/j.bbrc.2023.03.021] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2023] [Accepted: 03/08/2023] [Indexed: 03/17/2023]
Abstract
Nicotinic acetylcholine receptors (nAChRs), initially characterized as ligand-gated ion channels mediating fast synaptic transmission, are now found in many non-excitable cells and mitochondria where they function in ion-independent manner and regulate vital cellular processes like apoptosis, proliferation, cytokine secretion. Here we show that the nAChRs of α7 subtype are present in the nuclei of liver cells and astrocytoma U373 cell line. As shown by lectin ELISA, the nuclear α7 nAChRs are mature glycoproteins that follow the standard rout of post-translational modifications in Golgi; however, their glycosylation profile is non-identical to that of mitochondrial nAChRs. They are exposed on the outer nuclear membrane and are found in combination with lamin B1. The nuclear α7 nAChRs are up-regulated in liver within 1 h after partial hepatectomy and in H2O2-treated U373 cells. As shown both in silico and experimentally, the α7 nAChR interacts with hypoxia-inducible factor HIF-1α and this interaction is impaired by α7-selective agonists PNU282987 and choline or type 2 positive allosteric modulator PNU120596, which prevent HIF-1α accumulation in the nuclei. Similarly, HIF-1α interacts with mitochondrial α7 nAChRs in U373 cells treated with dimethyloxalylglycine. It is concluded that functional α7 nAChRs influence HIF-1α translocation into the nucleus and mitochondria upon hypoxia.
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Affiliation(s)
- Olena Kalashnyk
- Palladin Institute of Biochemistry NAS of Ukraine, 9, Leontovycha str., 01054, Kyiv, Ukraine.
| | - Olena Lykhmus
- Palladin Institute of Biochemistry NAS of Ukraine, 9, Leontovycha str., 01054, Kyiv, Ukraine.
| | - Lyudmyla Koval
- Palladin Institute of Biochemistry NAS of Ukraine, 9, Leontovycha str., 01054, Kyiv, Ukraine.
| | - Kateryna Uspenska
- Palladin Institute of Biochemistry NAS of Ukraine, 9, Leontovycha str., 01054, Kyiv, Ukraine.
| | - Maria Obolenskaya
- Institute of Molecular Biology and Genetics NAS of Ukraine, 150, Zabolotnogo str., 03143, Kyiv, Ukraine.
| | - Volodymyr Chernyshov
- Palladin Institute of Biochemistry NAS of Ukraine, 9, Leontovycha str., 01054, Kyiv, Ukraine.
| | - Serhiy Komisarenko
- Palladin Institute of Biochemistry NAS of Ukraine, 9, Leontovycha str., 01054, Kyiv, Ukraine.
| | - Maryna Skok
- Palladin Institute of Biochemistry NAS of Ukraine, 9, Leontovycha str., 01054, Kyiv, Ukraine.
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Kobara M, Amano T, Toba H, Nakata T. Nicorandil Suppresses Ischemia-Induced Norepinephrine Release and Ventricular Arrhythmias in Hypertrophic Hearts. Cardiovasc Drugs Ther 2023; 37:53-62. [PMID: 35895166 DOI: 10.1007/s10557-022-07369-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 07/19/2022] [Indexed: 01/14/2023]
Abstract
PURPOSE Ventricular arrhythmias (VAs) are a common cause of sudden death in acute myocardial infarction (MI), for which hypertension is a major risk factor. Nicorandil opens ATP-sensitive potassium (KATP) channels, which are expressed by nerve terminals and cardiomyocytes and regulate the release of norepinephrine (NE). However, the effects of nicorandil on ischemic NE release in cardiac tissue remain unclear. Therefore, we herein investigated whether nicorandil suppressed interstitial NE concentrations and VAs during acute MI in pressure overload-induced hypertrophic hearts. METHODS Rats were divided into two groups: an abdominal aortic constriction (AAC) group and sham-operated (Sham) group. Four weeks after constriction, cardiac geometry and functions were examined using echocardiography and hemodynamic analyses. Myocardial ischemia was induced by coronary artery occlusion for 100 min with or without the administration of nicorandil. VAs were assessed by electrocardiography, and NE concentrations in the ischemic region were measured using a micro-dialysis method. RESULTS AAC induced left ventricular hypertrophy with diastolic dysfunction. VAs markedly increased in the early phase (0-20 min) of ischemia in both groups and were more frequent in the AAC group. Cardiac interstitial NE concentrations were higher in the AAC group before ischemia and significantly increased during ischemia in both groups. Nicorandil significantly suppressed ischemia-induced VAs and NE increases in the AAC group. CONCLUSION Ischemia-induced VAs were more frequent in hypertrophic hearts and associated with high interstitial concentrations of NE. The attenuation of ischemia-induced increases in NE through neuronal KATP opening by nicorandil may suppress ischemia-induced VAs in hypertrophic hearts.
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Affiliation(s)
- Miyuki Kobara
- Department of Clinical Pharmacology, Division of Pathological Science, Kyoto Pharmaceutical University, 5 Misasagi Nakauchi-cho, Yamashina-ku, Kyoto, 607-8414, Japan.
| | - Toshihiro Amano
- Department of Clinical Pharmacology, Division of Pathological Science, Kyoto Pharmaceutical University, 5 Misasagi Nakauchi-cho, Yamashina-ku, Kyoto, 607-8414, Japan
| | - Hiroe Toba
- Department of Clinical Pharmacology, Division of Pathological Science, Kyoto Pharmaceutical University, 5 Misasagi Nakauchi-cho, Yamashina-ku, Kyoto, 607-8414, Japan
| | - Tetsuo Nakata
- Department of Clinical Pharmacology, Division of Pathological Science, Kyoto Pharmaceutical University, 5 Misasagi Nakauchi-cho, Yamashina-ku, Kyoto, 607-8414, Japan
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Prenatal hypoxia affected endothelium-dependent vasodilation in mesenteric arteries of aged offspring via increased oxidative stress. Hypertens Res 2019; 42:863-875. [DOI: 10.1038/s41440-018-0181-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2018] [Revised: 11/09/2018] [Accepted: 11/14/2018] [Indexed: 12/27/2022]
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Scott AL, Zhang M, Nurse CA. Enhanced BDNF signalling following chronic hypoxia potentiates catecholamine release from cultured rat adrenal chromaffin cells. J Physiol 2016; 593:3281-99. [PMID: 26095976 DOI: 10.1113/jp270725] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2015] [Accepted: 06/06/2015] [Indexed: 12/19/2022] Open
Abstract
KEY POINTS We investigated the role of the neurotrophin BDNF signalling via the TrkB receptor in rat adrenomedullary chromaffin cells (AMCs) exposed to normoxia (Nox; 21% O2) and chronic hypoxia (CHox; 2% O2) in vitro for ∼ 48 h. TrkB receptor expression was upregulated in primary AMCs and in immortalized chromaffin (MAH) cells exposed to CHox; this effect was absent in MAH cells deficient in the transcription factor, hypoxia inducible factor (HIF)-2α. Relative to normoxic controls, activation of the TrkB receptor in chronically hypoxic AMCs led to a marked increase in membrane excitability, intracellular [Ca(2+)], and catecholamine secretion. The BDNF-induced rise of intracellular [Ca(2+)] in CHox cells was sensitive to the selective T-type Ca(2+) channel blocker TTA-P2 and tetrodotoxin (TTX), suggesting key roles of low threshold T-type Ca(2+) and voltage-gated Na(+) channels in the signalling pathway. Environmental stressors, including chronic hypoxia, enhance the ability of adrenomedullary chromaffin cells (AMCs) to secrete catecholamines; however, the underlying molecular mechanisms remain unclear. Here, we investigated the role of brain-derived neurotrophic factor (BDNF) signalling in rat AMCs exposed to chronic hypoxia. In rat adrenal glands, BDNF and its tropomyosin-related kinase B (TrkB) receptor are highly expressed in the cortex and medulla, respectively. Exposure of AMCs to chronic hypoxia (2% O2; 48 h) in vitro caused a significant increase to TrkB mRNA expression. A similar increase was observed in an immortalized chromaffin cell line (MAH cells); however, it was absent in MAH cells deficient in the transcription factor HIF-2α. A specific TrkB agonist, 7,8-dihydroxyflavone (7,8-DHF), stimulated quantal catecholamine secretion from chronically hypoxic (CHox; 2% O2) AMCs to a greater extent than normoxic (Nox; 21% O2) controls. Activation of TrkB by BDNF or 7,8-DHF increased intracellular Ca(2+) ([Ca(2+)]i), an effect that was significantly larger in CHox cells. The 7,8-DHF-induced [Ca(2+)]i rise was sensitive to the tyrosine kinase inhibitor K252a and nickel (2 mm), but not the Ca(2+) store-depleting agent cyclopiazonic acid. Blockade of T-type calcium channels with TTA-P2 (1 μm) or voltage-gated Na(+) channels with TTX inhibited BDNF-induced [Ca(2+)]i increases. BDNF also induced a dose-dependent enhancement of action potential firing in CHox cells. These data demonstrate that during chronic hypoxia, enhancement of BDNF-TrkB signalling increases voltage-dependent Ca(2+) influx and catecholamine secretion in chromaffin cells, and that T-type Ca(2+) channels play a key role in the signalling pathway.
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Affiliation(s)
- Angela L Scott
- Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4K1, Canada
| | - Min Zhang
- Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4K1, Canada
| | - Colin A Nurse
- Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4K1, Canada
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Ohya S, Kito H, Hatano N, Muraki K. Recent advances in therapeutic strategies that focus on the regulation of ion channel expression. Pharmacol Ther 2016; 160:11-43. [PMID: 26896566 DOI: 10.1016/j.pharmthera.2016.02.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
A number of different ion channel types are involved in cell signaling networks, and homeostatic regulatory mechanisms contribute to the control of ion channel expression. Profiling of global gene expression using microarray technology has recently provided novel insights into the molecular mechanisms underlying the homeostatic and pathological control of ion channel expression. It has demonstrated that the dysregulation of ion channel expression is associated with the pathogenesis of neural, cardiovascular, and immune diseases as well as cancers. In addition to the transcriptional, translational, and post-translational regulation of ion channels, potentially important evidence on the mechanisms controlling ion channel expression has recently been accumulated. The regulation of alternative pre-mRNA splicing is therefore a novel therapeutic strategy for the treatment of dominant-negative splicing disorders. Epigenetic modification plays a key role in various pathological conditions through the regulation of pluripotency genes. Inhibitors of pre-mRNA splicing and histone deacetyalase/methyltransferase have potential as potent therapeutic drugs for cancers and autoimmune and inflammatory diseases. Moreover, membrane-anchoring proteins, lysosomal and proteasomal degradation-related molecules, auxiliary subunits, and pharmacological agents alter the protein folding, membrane trafficking, and post-translational modifications of ion channels, and are linked to expression-defect channelopathies. In this review, we focused on recent insights into the transcriptional, spliceosomal, epigenetic, and proteasomal regulation of ion channel expression: Ca(2+) channels (TRPC/TRPV/TRPM/TRPA/Orai), K(+) channels (voltage-gated, KV/Ca(2+)-activated, KCa/two-pore domain, K2P/inward-rectifier, Kir), and Ca(2+)-activated Cl(-) channels (TMEM16A/TMEM16B). Furthermore, this review highlights expression of these ion channels in expression-defect channelopathies.
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Affiliation(s)
- Susumu Ohya
- Department of Pharmacology, Division of Pathological Sciences, Kyoto Pharmaceutical University, Kyoto 607-8414, Japan.
| | - Hiroaki Kito
- Department of Pharmacology, Division of Pathological Sciences, Kyoto Pharmaceutical University, Kyoto 607-8414, Japan
| | - Noriyuki Hatano
- Laboratory of Cellular Pharmacology, School of Pharmacy, Aichi-Gakuin University, Nagoya 464-8650, Japan
| | - Katsuhiko Muraki
- Laboratory of Cellular Pharmacology, School of Pharmacy, Aichi-Gakuin University, Nagoya 464-8650, Japan.
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Zhu X, Gao Q, Tu Q, Zhong Y, Zhu D, Mao C, Xu Z. Prenatal hypoxia enhanced angiotensin II-mediated vasoconstriction via increased oxidative signaling in fetal rats. Reprod Toxicol 2016; 60:21-8. [PMID: 26796766 DOI: 10.1016/j.reprotox.2016.01.001] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Revised: 12/29/2015] [Accepted: 01/08/2016] [Indexed: 02/07/2023]
Abstract
Toxic factors could cause in utero hypoxia, and prenatal hypoxia (PH) increased incidence of cardiovascular diseases in late life. It is unclear whether/how PH causes vascular injury during fetal life. This study found that PH significantly increased angiotensin II (Ang II)-mediated vessel contractions in fetal thoracic aortas, which was blocked by losartan, not PD123319, indicating that AT1 receptors played a dominant role in the enhanced fetal vasoconstriction following hypoxia. Prenatal hypoxia increased superoxide production and decreased superoxide dismutase (SOD) expression, associated with the enhanced NADPH oxidase (Nox) 4, but not Nox1 or Nox2 in fetal aortas. Ang II-increased vasoconstriction was inhibited by Nox inhibitor apocynin and SOD mimetic blocker tempol. These findings suggested that PH resulted in Ang II/AT1R-mediated fetal vascular hypertensive re-activity via pathways of Nox4-dependent oxidative stress, providing new information regarding the impact of PH on the functional and molecular development of fetal vascular systems.
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Affiliation(s)
- Xiaolin Zhu
- Institute for Fetology and Reproductive Medicine Center, The First Affiliated Hospital of Soochow University, Suzhou, China
| | - Qinqin Gao
- Institute for Fetology and Reproductive Medicine Center, The First Affiliated Hospital of Soochow University, Suzhou, China
| | - Qing Tu
- Institute for Fetology and Reproductive Medicine Center, The First Affiliated Hospital of Soochow University, Suzhou, China
| | - Yuan Zhong
- Institute for Fetology and Reproductive Medicine Center, The First Affiliated Hospital of Soochow University, Suzhou, China
| | - Di Zhu
- Institute for Fetology and Reproductive Medicine Center, The First Affiliated Hospital of Soochow University, Suzhou, China
| | - Caiping Mao
- Institute for Fetology and Reproductive Medicine Center, The First Affiliated Hospital of Soochow University, Suzhou, China
| | - Zhice Xu
- Institute for Fetology and Reproductive Medicine Center, The First Affiliated Hospital of Soochow University, Suzhou, China; Center for Perinatal Biology, Loma Linda University, CA, USA.
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Bae WJ, Shin MR, Kang SK, Zhang-Jun, Kim JY, Lee SC, Kim EC. HIF-2 Inhibition Supresses Inflammatory Responses and Osteoclastic Differentiation in Human Periodontal Ligament Cells. J Cell Biochem 2015; 116:1241-55. [DOI: 10.1002/jcb.25078] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2014] [Accepted: 12/18/2014] [Indexed: 01/20/2023]
Affiliation(s)
- Won-Jung Bae
- Department of Oral and Maxillofacial Pathology; Research Center for Tooth and Periodontal Regeneration (MRC); School of Dentistry; Kyung Hee University; Seoul Republic of Korea
| | - Mee-Ran Shin
- Department of Prosthodontics; Dongatn Sacred Heart Hospital; Hallym University; Dongtan South Korea
| | - Soo-Kyung Kang
- Department of Oral Medicine; School of Dentistry; Kyung Hee University; Seoul Republic of Korea
| | - Zhang-Jun
- Department of Oral and Maxillofacial Pathology; Research Center for Tooth and Periodontal Regeneration (MRC); School of Dentistry; Kyung Hee University; Seoul Republic of Korea
| | - Jun-Yeol Kim
- Department of Oral and Maxillofacial Pathology; Research Center for Tooth and Periodontal Regeneration (MRC); School of Dentistry; Kyung Hee University; Seoul Republic of Korea
| | - Sang-Cheon Lee
- Department of Maxillofacial Biomedical Engineering; School of Dentistry; Kyung Hee University; Seoul Republic of Korea
| | - Eun-Cheol Kim
- Department of Oral and Maxillofacial Pathology; Research Center for Tooth and Periodontal Regeneration (MRC); School of Dentistry; Kyung Hee University; Seoul Republic of Korea
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Salman S, Buttigieg J, Nurse CA. Ontogeny of O2 and CO2//H+ chemosensitivity in adrenal chromaffin cells: role of innervation. ACTA ACUST UNITED AC 2014; 217:673-81. [PMID: 24574383 DOI: 10.1242/jeb.086165] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The adrenal medulla plays a key role in the physiological responses of developing and mature mammals by releasing catecholamines (CAT) during stress. In rodents and humans, the innervation of CAT-producing, adrenomedullary chromaffin cells (AMCs) is immature or absent during early postnatal life, when these cells possess 'direct' hypoxia- and CO2/H(+)-chemosensing mechanisms. During asphyxial stressors at birth, these mechanisms contribute to a CAT surge that is critical for adaptation to extra-uterine life. These direct chemosensing mechanisms regress postnatally, in parallel with maturation of splanchnic innervation. Here, we review the evidence that neurotransmitters released from the splanchnic nerve during innervation activate signaling cascades that ultimately cause regression of direct AMC chemosensitivity to hypoxia and hypercapnia. In particular, we consider the roles of cholinergic and opioid receptor signaling, given that splanchnic nerves release acetylcholine and opiate peptides onto their respective postsynaptic nicotinic and opioid receptors on AMCs. Recent in vivo and in vitro studies in the rat suggest that interactions involving α7 nicotinic acetylcholine receptors (nAChRs), the hypoxia inducible factor (HIF)-2α signaling pathway, protein kinases and ATP-sensitive K(+) (KATP) channels contribute to the selective suppression of hypoxic chemosensitivity. In contrast, interactions involving μ- and/or δ-opiod receptor signaling pathways contribute to the suppression of both hypoxic and hypercapnic chemosensitivity, via regulation of the expression of KATP channels and carbonic anhydrase (CA I and II), respectively. These data suggest that the ontogeny of O2 and CO2/H(+) chemosensitivity in chromaffin cells can be regulated by the tonic release of presynaptic neurotransmitters.
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Affiliation(s)
- Shaima Salman
- Department of Biology, McMaster University, Hamilton, ON, Canada, L8S 4K1
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Salman S, Holloway AC, Nurse CA. Chronic opioids regulate KATP channel subunit Kir6.2 and carbonic anhydrase I and II expression in rat adrenal chromaffin cells via HIF-2α and protein kinase A. Am J Physiol Cell Physiol 2014; 307:C266-77. [PMID: 24898587 DOI: 10.1152/ajpcell.00135.2014] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
At birth, asphyxial stressors such as hypoxia and hypercapnia are important physiological stimuli for adrenal catecholamine release that is critical for the proper transition to extrauterine life. We recently showed that chronic opioids blunt chemosensitivity of neonatal rat adrenomedullary chromaffin cells (AMCs) to hypoxia and hypercapnia. This blunting was attributable to increased ATP-sensitive K(+) (KATP) channel and decreased carbonic anhydrase (CA) I and II expression, respectively, and involved μ- and δ-opioid receptor signaling pathways. To address underlying molecular mechanisms, we first exposed an O2- and CO2-sensitive, immortalized rat chromaffin cell line (MAH cells) to combined μ {[d-Arg(2),Ly(4)]dermorphin-(1-4)-amide}- and δ ([d-Pen(2),5,P-Cl-Phe(4)]enkephalin)-opioid agonists (2 μM) for ∼7 days. Western blot and quantitative real-time PCR analysis revealed that chronic opioids increased KATP channel subunit Kir6.2 and decreased CAII expression; both effects were blocked by naloxone and were absent in hypoxia-inducible factor (HIF)-2α-deficient MAH cells. Chronic opioids also stimulated HIF-2α accumulation along a time course similar to Kir6.2. Chromatin immunoprecipitation assays on opioid-treated cells revealed the binding of HIF-2α to a hypoxia response element in the promoter region of the Kir6.2 gene. The opioid-induced regulation of Kir6.2 and CAII was dependent on protein kinase A, but not protein kinase C or calmodulin kinase, activity. Interestingly, a similar pattern of HIF-2α, Kir6.2, and CAII regulation (including downregulation of CAI) was replicated in chromaffin tissue obtained from rat pups born to dams exposed to morphine throughout gestation. Collectively, these data reveal novel mechanisms by which chronic opioids blunt asphyxial chemosensitivity in AMCs, thereby contributing to abnormal arousal responses in the offspring of opiate-addicted mothers.
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Affiliation(s)
- Shaima Salman
- Department of Biology, McMaster University, Hamilton, Ontario, Canada; and
| | - Alison C Holloway
- Division of Reproductive Biology, Department of Obstetrics and Gynecology Division of Reproductive Biology, McMaster University, Hamilton, Ontario, Canada
| | - Colin A Nurse
- Department of Biology, McMaster University, Hamilton, Ontario, Canada; and
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Salman S, Buttigieg J, Zhang M, Nurse CA. Chronic exposure of neonatal rat adrenomedullary chromaffin cells to opioids in vitro blunts both hypoxia and hypercapnia chemosensitivity. J Physiol 2012; 591:515-29. [PMID: 23148319 DOI: 10.1113/jphysiol.2012.243477] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
At birth, rat adrenomedullary chromaffin cells (AMCs) respond directly to asphyxial stressors such as hypoxia and hypercapnia by triggering catecholamine secretion, which is critical for proper transition to extrauterine life. These non-neurogenic responses are suppressed postnatally in parallel with the development of splanchnic innervation, and reappear following denervation of the adult adrenal gland. To test whether neural factors released from the splanchnic nerve may regulate AMC chemosensitivity, we previously showed that nicotinic agonists in utero and in vitro suppressed hypoxia, but not hypercapnia, sensitivity. Here, we considered the potential role of opiate peptides which are also released from the splanchnic nerve and act via postsynaptic μ-, δ- and -opioid receptors. Treatment of neonatal rat AMC cultures for ∼1 week with μ- and/or δ- (but not ) opioid agonists (2 μm) led to a marked suppression of both hypoxia and hypercapnia sensitivity, as measured by K(+) current inhibition and membrane depolarization; co-incubation with naloxone prevented the effects of combined opioids. The suppression of hypoxia sensitivity was attributable to upregulation of K(ATP) current density and the K(ATP) channel subunit Kir6.2, and was reversed by the K(ATP) channel blocker, glibenclamide. By contrast, suppression of hypercapnia sensitivity was associated with down-regulation of two key mediators of CO(2) sensing, i.e. carbonic anhydrase I and II. Collectively, these studies point to a novel role for opioid receptor signalling in the developmental regulation of chromaffin cell chemosensitivity, and suggest that prenatal exposure to opioid drugs could lead to impaired arousal responses in the neonate.
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Affiliation(s)
- Shaima Salman
- Department of Biology, McMaster University, Hamilton, Ontario L8S 4K1, Canada
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