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Decreased content of ascorbic acid (vitamin C) in the brain of knockout mouse models of Na+,K+-ATPase-related neurologic disorders. PLoS One 2021; 16:e0246678. [PMID: 33544780 PMCID: PMC7864419 DOI: 10.1371/journal.pone.0246678] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2020] [Accepted: 01/23/2021] [Indexed: 12/21/2022] Open
Abstract
Na+,K+-ATPase is a crucial protein responsible for maintaining the electrochemical gradients across the cell membrane. The Na+,K+-ATPase is comprised of catalytic α, β, and γ subunits. In adult brains, the α3 subunit, encoded by ATP1A3, is predominantly expressed in neurons, whereas the α2 subunit, encoded by ATP1A2, is expressed in glial cells. In foetal brains, the α2 is expressed in neurons as well. Mutations in α subunits cause a variety of neurologic disorders. Notably, the onset of symptoms in ATP1A2- and ATP1A3-related neurologic disorders is usually triggered by physiological or psychological stressors. To gain insight into the distinct roles of the α2 and α3 subunits in the developing foetal brain, whose developmental dysfunction may be a predisposing factor of neurologic disorders, we compared the phenotypes of mouse foetuses with double homozygous knockout of Atp1a2 and Atp1a3 (α2α3-dKO) to those with single knockout. The brain haemorrhage phenotype of α2α3-dKO was similar to that of homozygous knockout of the gene encoding ascorbic acid (ASC or vitamin C) transporter, SVCT2. The α2α3-dKO brain showed significantly decreased level of ASC compared with the wild-type (WT) and single knockout. We found that the ASC content in the basal ganglia and cerebellum was significantly lower in the adult Atp1a3 heterozygous knockout mouse (α3-HT) than in the WT. Interestingly, we observed a significant decrease in the ASC level in the basal ganglia and cerebellum of α3-HT in the peripartum period, during which mice are under physiological stress. These observations indicate that the α2 and α3 subunits independently contribute to the ASC level in the foetal brain and that the α3 subunit contributes to ASC transport in the adult basal ganglia and cerebellum. We propose that decreases in ASC levels may affect neural network development and are linked to the pathophysiology of ATP1A2- and ATP1A3-related neurologic disorders.
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Hammann J, Bassetti D, White R, Luhmann HJ, Kirischuk S. α2 isoform of Na +,K +-ATPase via Na +,Ca 2+ exchanger modulates myelin basic protein synthesis in oligodendrocyte lineage cells in vitro. Cell Calcium 2018; 73:1-10. [PMID: 29880193 DOI: 10.1016/j.ceca.2018.03.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Revised: 03/05/2018] [Accepted: 03/25/2018] [Indexed: 11/26/2022]
Abstract
Oligodendrocytes in the CNS myelinate neuronal axons, facilitating rapid propagation of action potentials. Myelin basic protein (MBP) is an essential component of myelin and its absence results in severe hypomyelination. In oligodendrocyte lineage cell (OLC) monocultures MBP synthesis starts at DIV4. Ouabain (10 nM), a Na+,K+-ATPase (NKA) blocker, stimulates MBP synthesis. As OLCs express the α2 isoform of NKA (α2-NKA) that has a high affinity for ouabain, we hypothesized that α2-NKA mediates this effect. Knockdown of α2-NKA with small interfering (si)RNA (α2-siRNA) significantly potentiated MBP synthesis at DIV4 and 5. This effect was completely blocked by KB-R7943 (1 μM), a Na+,Ca2+ exchanger (NCX) antagonist. α2-NKA ablation increased the frequency of NCX-mediated spontaneous Ca2+ transients ([Ca2+]t) at DIV4, whereas in control OLC cultures comparable frequency of [Ca2+]t was observed at DIV5. At DIV6 almost no [Ca2+]t were observed either in control or in α2-siRNA-treated cultures. Immunocytochemical analyses showed that α2-NKA co-localizes with MBP in proximal processes of immature OLCs but is only weakly present in MBP-enriched membrane sheets. Knockdown of α2-NKA in cortical slice cultures did not change MBP levels but reduced co-localization of neurofilament- and MBP-positive compartments. We conclude that α2-NKA activity in OLCs affects NCX-mediated [Ca2+]t and the onset of MBP synthesis. We suggest therefore that neuronal activity, presumably in form of local extracellular [K+] changes, might locally influence NCX-mediated [Ca2+]t in OLC processes thus triggering local MBP synthesis in the vicinity of an active axon.
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Affiliation(s)
- Jens Hammann
- Institute of Physiology, University Medical Center of the Johannes Gutenberg University Mainz, Duesbergweg 6, D-55128 Mainz, Germany
| | - Davide Bassetti
- Institute of Physiology, University Medical Center of the Johannes Gutenberg University Mainz, Duesbergweg 6, D-55128 Mainz, Germany
| | - Robin White
- Institute of Physiology, University Medical Center of the Johannes Gutenberg University Mainz, Duesbergweg 6, D-55128 Mainz, Germany
| | - Heiko J Luhmann
- Institute of Physiology, University Medical Center of the Johannes Gutenberg University Mainz, Duesbergweg 6, D-55128 Mainz, Germany
| | - Sergei Kirischuk
- Institute of Physiology, University Medical Center of the Johannes Gutenberg University Mainz, Duesbergweg 6, D-55128 Mainz, Germany.
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Hertz L, Chen Y. Glycogenolysis, an Astrocyte-Specific Reaction, is Essential for Both Astrocytic and Neuronal Activities Involved in Learning. Neuroscience 2017; 370:27-36. [PMID: 28668486 DOI: 10.1016/j.neuroscience.2017.06.025] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2017] [Revised: 06/10/2017] [Accepted: 06/19/2017] [Indexed: 01/26/2023]
Abstract
In brain glycogen, formed from glucose, is degraded (glycogenolysis) in astrocytes but not in neurons. Although most of the degradation follows the same pathway as glucose, its breakdown product, l-lactate, is released from astrocytes in larger amounts than glucose when glycogenolysis is activated by noradrenaline. However, this is not the case when glycogenolysis is activated by high potassium ion (K+) concentrations - possibly because noradrenaline in contrast to high K+ stimulates glycogenolysis by an increase not only in free cytosolic Ca2+ concentration ([Ca2+]i) but also in cyclic AMP (c-AMP), which may increase the expression of the monocarboxylate transporter through which it is released. Several transmitters activate glycogenolysis in astrocytes and do so at different time points after training. This stimulation is essential for memory consolidation because glycogenolysis is necessary for uptake of K+ and stimulates formation of glutamate from glucose, and therefore is needed both for removal of increased extracellular K+ following neuronal excitation (which initially occurs into astrocytes) and for formation of transmitter glutamate and GABA. In addition the released l-lactate has effects on neurons which are essential for learning and for learning-related long-term potentiation (LTP), including induction of the neuronal gene Arc/Arg3.1 and activation of gene cascades mediated by CREB and cofilin. Inhibition of glycogenolysis blocks learning, LTP and all related molecular events, but all changes can be reversed by injection of l-lactate. The effect of extracellular l-lactate is due to both astrocyte-mediated signaling which activates noradrenergic activity on all brain cells and to a minor uptake, possibly into dendritic spines.
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Affiliation(s)
- Leif Hertz
- Laboratory of Metabolic Brain Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical University, Shenyang, PR China
| | - Ye Chen
- Henry M. Jackson Foundation, Bethesda, MD 20817, USA.
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Hertz L, Chen Y. Importance of astrocytes for potassium ion (K+) homeostasis in brain and glial effects of K+ and its transporters on learning. Neurosci Biobehav Rev 2016; 71:484-505. [DOI: 10.1016/j.neubiorev.2016.09.018] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2016] [Revised: 08/12/2016] [Accepted: 09/23/2016] [Indexed: 10/20/2022]
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Isaksen TJ, Lykke-Hartmann K. Insights into the Pathology of the α2-Na(+)/K(+)-ATPase in Neurological Disorders; Lessons from Animal Models. Front Physiol 2016; 7:161. [PMID: 27199775 PMCID: PMC4854887 DOI: 10.3389/fphys.2016.00161] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Accepted: 04/15/2016] [Indexed: 12/12/2022] Open
Abstract
A functional Na+/K+-ATPase consists of a catalytic α subunit and a regulatory β subunit. Four α isoforms of the Na+/K+-ATPase are found in mammals, each with a unique expression pattern and catalytic activity. The α2 isoform, encoded by the ATP1A2 gene, is primarily found in the central nervous system (CNS) and in heart-, skeletal- and smooth muscle tissues. In the CNS, the α2 isoform is mainly expressed in glial cells. In particular, the α2 isoform is found in astrocytes, important for astrocytic K+ clearance and, consequently, the indirect uptake of neurotransmitters. Both processes are essential for proper brain activity, and autosomal dominantly mutations in the ATP1A2 gene cause the neurological disorder Familial hemiplegic migraine type 2 (FHM2). FHM2 is a severe subtype of migraine with aura including temporary numbness or weakness, and affecting only one side of the body. FHM2 patients often suffer from neurological comorbidities such as seizures, sensory disturbances, cognitive impairment, and psychiatric manifestations. The functional consequences of FHM2 disease mutations leads to a partial or complete loss of function of pump activity; however, a clear phenotype-genotype correlation has yet to be elucidated. Gene-modified mouse models targeting the Atp1a2 gene have proved instrumental in the understanding of the pathology of FHM2. Several Atp1a2 knockout (KO) mice targeting different exons have been reported. Homozygous Atp1a2 KO mice die shortly after birth due to respiratory malfunction resulting from abnormal Cl− homeostasis in brainstem neurons. Heterozygous KO mice are viable, but display altered behavior and neurological deficits such as altered spatial learning, decreased motor activity and enhanced fear/anxiety compared to wild type mice. FHM2 knock-in (KI) mouse models carrying the human in vivo disease mutations W887R and G301R have also been reported. Both models display altered cortical spreading depression (CSD) and point to deficits in the glutamatergic system as the main underlying mechanism of FHM2.
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Affiliation(s)
- Toke J Isaksen
- Department of Biomedicine, Aarhus UniversityAarhus, Denmark; Centre for Membrane Pumps in Cells and Disease-PUMPKIN, Danish National Research Foundation, Department of Molecular Biology and Genetics, Aarhus UniversityAarhus, Denmark
| | - Karin Lykke-Hartmann
- Department of Biomedicine, Aarhus UniversityAarhus, Denmark; Centre for Membrane Pumps in Cells and Disease-PUMPKIN, Danish National Research Foundation, Department of Molecular Biology and Genetics, Aarhus UniversityAarhus, Denmark; Aarhus Institute of Advanced Studies, Aarhus UniversityAarhus, Denmark
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Ionic transporter activity in astrocytes, microglia, and oligodendrocytes during brain ischemia. J Cereb Blood Flow Metab 2013; 33:969-82. [PMID: 23549380 PMCID: PMC3705429 DOI: 10.1038/jcbfm.2013.44] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/05/2012] [Revised: 02/27/2013] [Accepted: 02/28/2013] [Indexed: 01/09/2023]
Abstract
Glial cells constitute a large percentage of cells in the nervous system. During recent years, a large number of studies have critically attributed to glia a new role which no longer reflects the long-held view that glia constitute solely a silent and passive supportive scaffolding for brain cells. Indeed, it has been hypothesized that glia, partnering neurons, have a much more actively participating role in brain function. Alteration of intraglial ionic homeostasis in response to ischemic injury has a crucial role in inducing and maintaining glial responses in the ischemic brain. Therefore, glial transporters as potential candidates in stroke intervention are becoming promising targets to enhance an effective and additional therapy for brain ischemia. In this review, we will describe in detail the role played by ionic transporters in influencing astrocyte, microglia, and oligodendrocyte activity and the implications that these transporters have in the progression of ischemic lesion.
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Bøttger P, Doğanlı C, Lykke-Hartmann K. Migraine- and dystonia-related disease-mutations of Na+/K+-ATPases: relevance of behavioral studies in mice to disease symptoms and neurological manifestations in humans. Neurosci Biobehav Rev 2011; 36:855-71. [PMID: 22067897 DOI: 10.1016/j.neubiorev.2011.10.005] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2011] [Revised: 10/20/2011] [Accepted: 10/26/2011] [Indexed: 10/15/2022]
Abstract
The two autosomal dominantly inherited neurological diseases: familial hemiplegic migraine type 2 (FHM2) and familial rapid-onset of dystonia-parkinsonism (Familial RDP) are caused by in vivo mutations of specific alpha subunits of the sodium-potassium pump (Na(+)/K(+)-ATPase). Intriguingly, patients with classical FHM2 and RDP symptoms additionally suffer from other manifestations, such as epilepsy/seizures and developmental disabilities. Recent studies of FHM2 and RDP mouse models provide valuable tools for dissecting the vital roles of the Na(+)/K(+)-ATPases, and we discuss their relevance to the complex patient symptoms and manifestations. Thus, it is interesting that mouse models targeting a specific α-isoform cause different, although still comparable, phenotypes consistent with classical symptoms and other manifestations observed in FHM2 and RDP patients. This review highlights that use of mouse models have broad potentials for future research concerning migraine and dystonia-related diseases, which will contribute towards understanding the, yet unknown, pathophysiologies.
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Affiliation(s)
- Pernille Bøttger
- Centre for Membrane Pumps in Cells and Disease-PUMPKIN, Danish National Research Foundation, Denmark; Department of Biomedicine, Aarhus University, Ole Worms Allé 3, Aarhus C, Denmark
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Das G, Gopalakrishnan A, Faisal M, Mallick B. Stimulatory role of calcium in rapid eye movement sleep deprivation–induced noradrenaline-mediated increase in Na-K-ATPase activity in rat brain. Neuroscience 2008; 155:76-89. [DOI: 10.1016/j.neuroscience.2008.04.069] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2007] [Revised: 03/07/2008] [Accepted: 04/28/2008] [Indexed: 11/16/2022]
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Yamaguchi Y, Miyagi Y, Baba H. Two-dimensional electrophoresis with cationic detergents: A powerful tool for the proteomic analysis of myelin proteins. Part 2: Analytical aspects. J Neurosci Res 2008; 86:766-75. [DOI: 10.1002/jnr.21549] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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Werner HB, Kuhlmann K, Shen S, Uecker M, Schardt A, Dimova K, Orfaniotou F, Dhaunchak A, Brinkmann BG, Möbius W, Guarente L, Casaccia-Bonnefil P, Jahn O, Nave KA. Proteolipid protein is required for transport of sirtuin 2 into CNS myelin. J Neurosci 2007; 27:7717-30. [PMID: 17634366 PMCID: PMC2676101 DOI: 10.1523/jneurosci.1254-07.2007] [Citation(s) in RCA: 193] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Mice lacking the expression of proteolipid protein (PLP)/DM20 in oligodendrocytes provide a genuine model for spastic paraplegia (SPG-2). Their axons are well myelinated but exhibit impaired axonal transport and progressive degeneration, which is difficult to attribute to the absence of a single myelin protein. We hypothesized that secondary molecular changes in PLP(null) myelin contribute to the loss of PLP/DM20-dependent neuroprotection and provide more insight into glia-axonal interactions in this disease model. By gel-based proteome analysis, we identified >160 proteins in purified myelin membranes, which allowed us to systematically monitor the CNS myelin proteome of adult PLP(null) mice, before the onset of disease. We identified three proteins of the septin family to be reduced in abundance, but the nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase sirtuin 2 (SIRT2) was virtually absent. SIRT2 is expressed throughout the oligodendrocyte lineage, and immunoelectron microscopy revealed its association with myelin. Loss of SIRT2 in PLP(null) was posttranscriptional, suggesting that PLP/DM20 is required for its transport into the myelin compartment. Because normal SIRT2 activity is controlled by the NAD+/NADH ratio, its function may be coupled to the axo-glial metabolism and the long-term support of axons by oligodendrocytes.
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Affiliation(s)
- Hauke B Werner
- Department of Neurogenetics, Max Planck Institute of Experimental Medicine, D-37075 Goettingen, Germany.
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Kahlert S, Reiser G. Glial perspectives of metabolic states during cerebral hypoxia—calcium regulation and metabolic energy. Cell Calcium 2004; 36:295-302. [PMID: 15261485 DOI: 10.1016/j.ceca.2004.02.009] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2004] [Accepted: 02/18/2004] [Indexed: 11/23/2022]
Abstract
Cooperation between astrocytes and neurons is a unique interaction between two highly specialized cell types of the brain. Therefore, lack of nutrient supply during ischemia requires tight coordination of metabolism between astrocytes and neurons to keep the brain functions intact. To understand the impact of energy limitation on astrocytes, the functions of astrocytes have to be considered: (i) supplementation of neuronal cells, (ii) modulation of the extracellular milieu, mainly of the glutamate level, and (iii) elimination of reactive oxygen species (ROS). In cultured astrocytes and neurons inhibition of oxidative phosphorylation, using rotenone, was tested. Interestingly, this had only a negligible effect on Ca2+ homeostasis in astrocytes, even in combination with a severe glutamate stress. In contrast, in neurons glutamate in the presence of rotenone induced Ca2+ deregulation. Ca2+ homeostasis is very critical for cell survival. A massive and prolonged Ca2+ rise will lead to deregulation of many processes in such a way that the cells affected can hardly survive. Ca2+ homeostasis depends on the energy-consuming processes, which maintain the steep gradient between intracellular and extracellular Ca2+ concentration. Deprivation of oxygen and glucose during ischemia leads to a depletion of ATP in the brain, due to inhibited glycolytic and mitochondrial activity, whereas energy-consuming processes like ion pumps drain the ATP pools. On the other hand, specific mechanisms can protect brain structures against the massive insult of ischemia. Glycogen, stored in astrocytes, can maintain both neurons and astrocytes alive during short limitation of oxygen and glucose. Moreover, astrocytes can fuel ATP generation by providing lactate for neurons.
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Affiliation(s)
- Stefan Kahlert
- Institut für Neurobiochemie, Medizinische Fakultät der Otto-von-Guericke-Universität Magdeburg, Leipziger Strabetae 44, D-39120 Magdeburg, Germany
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Ong MD, Payne DM, Garner MH. Differential protein expression in lens epithelial whole-mounts and lens epithelial cell cultures. Exp Eye Res 2003; 77:35-49. [PMID: 12823986 DOI: 10.1016/s0014-4835(03)00090-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
PURPOSE Lens fibergenesis is a problem in several types of cataract and in the posterior capsular opacification following cataract surgery. To correct improper fiber differentiation or to prevent unwanted growth on the posterior capsule following cataract surgery requires a thorough understanding of normal and abnormal fiber formation. To this end, studies were initiated to characterize fiber differentiation in the bovine lens and in lens epithelial cell cultures. METHODS Indirect immunofluorescence and immunoblot analysis were employed to study the expression of vimentin, beta-crystallin, gamma-crystallin, filensin, aquaporin 0 and the Na, K-ATPase catalytic subunit isoforms (alpha1, alpha2, alpha3) in bovine lens epithelium whole-mounts as well as lens epithelial cell cultures propagated in medium containing 10% bovine serum or in medium supplemented with bovine serum concentrations < or =4%. RESULTS Three distinct cell types were observed in the bovine lens epithelium. The cells of the central zone were identified by a polarized distribution of two distinct Na, K-ATPase catalytic subunit isoforms, alpha1 to the apical (fiber side) and alpha3 to the basal (aqueous humor side) membranes. Lateral to the polarized central zone, was the germinative zone of cells, best characterized by perinuclear vimentin basket-like structures and the loss of polarized Na, K-ATPase catalytic subunit isoforms. Lateral to the germinative zone were the cells of the transition zone (meridinal rows) where expression of the lens specific proteins beta-crystallin, gamma-crystallin, filensin and aquaporin 0 as well as the lens fiber-, adipocyte- and brain glia-specific Na, K-ATPase catalytic subunit, alpha2 are expressed. The cultured cells propagated in medium supplemented with 10% serum bore no resemblance to any of the cells of the bovine lens epithelium whole-mounts. The cells propagated in the medium supplemented with the lower bovine serum levels resembled the differentiating fibers of the transition zone of the bovine lens epithelium whole-mounts as well as superficial cortical fibers. CONCLUSIONS Since the low-serum lens epithelial cell cultures bear a remarkable resemblance to early differentiating fibers, they are reasonable models for the study of early fiber differentiation or prevention of differentiation. The culture conditions employed do not yield the polarized cells of the central zone. Nor has the function of these polarized cells in lens fluid, nutrient and ion homeostasis been determined.
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Affiliation(s)
- Marcia D Ong
- Department of Pathology and Anatomy, Division of Cell Biology and Genetics, UNT Health Science Center, Fort Worth, TX 76107, USA
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Quintas LEM, Lafayette SSL, Caricati-Neto A, Jurkiewicz A, Noël F. Role of noradrenaline on the expression of the Na+/K+-ATPase alpha2 isoform and the contractility of cultured rat vas deferens. Biochem Pharmacol 2002; 64:1431-7. [PMID: 12417256 DOI: 10.1016/s0006-2952(02)01359-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Rat vasa deferentia were cultured for 3 days in Dulbecco's modified Eagle's medium in the absence or presence of 1 microM noradrenaline (NA) to investigate if the lack of NA release is the key factor to explain the selective reduction of the Na(+)/K(+)-ATPase alpha(2) isoform previously observed after in vivo denervation of this organ (Quintas et al., Biochem Pharmacol 2000;60:741-7). The lack of effects of the indirect sympathomimetic tyramine and the neuronal amine uptake blocker cocaine on NA curves indicated that cultured organs were denervated completely. Organ culture induced supersensitivity, expressed as a 6.3-fold increase of pD(2) and a 42% elevation of maximal contraction for NA but not for Ba(2+). Western blotting indicated that the level of the alpha(1) isoform of Na(+)/K(+)-ATPase was unchanged after organ culture, but the alpha(2) isoform was down-regulated drastically to levels that were barely detectable. The addition of NA to the culture medium did not prevent the reduction of alpha(2) expression although it did impede NA supersensitivity (in fact a 4-fold decrease of pD(2) and a 32% reduction of maximal response were observed after incubation in the presence of NA). A striking reduction of L-type Ca(2+) channel expression also was observed, indicated by an 85% decrease of [3H]isradipine binding sites. These data suggest that NA is a trophic factor relevant to the control of muscle contraction, mediated by alpha(1)-adrenoceptors, but not to the expression of either Na(+)/K(+)-ATPase or the L-type Ca(2+) channel.
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Affiliation(s)
- Luis Eduardo M Quintas
- Departamento de Farmacologia Básica e Clínica, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Cidade Universitária, 21941-590 Rio de Janeiro, Brazil
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