1
|
Altamura C, Desaphy JF, Conte D, De Luca A, Imbrici P. Skeletal muscle ClC-1 chloride channels in health and diseases. Pflugers Arch 2020; 472:961-975. [PMID: 32361781 DOI: 10.1007/s00424-020-02376-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2020] [Revised: 03/18/2020] [Accepted: 03/31/2020] [Indexed: 12/14/2022]
Abstract
In 1970, the study of the pathomechanisms underlying myotonia in muscle fibers isolated from myotonic goats highlighted the importance of chloride conductance for skeletal muscle function; 20 years later, the human ClC-1 chloride channel has been cloned; last year, the crystal structure of human protein has been solved. Over the years, the efforts of many researchers led to significant advances in acknowledging the role of ClC-1 in skeletal muscle physiology and the mechanisms through which ClC-1 dysfunctions lead to impaired muscle function. The wide spectrum of pathophysiological conditions associated with modification of ClC-1 activity, either as the primary cause, such as in myotonia congenita, or as a secondary adaptive mechanism in other neuromuscular diseases, supports the idea that ClC-1 is relevant to preserve not only for skeletal muscle excitability, but also for skeletal muscle adaptation to physiological or harmful events. Improving this understanding could open promising avenues toward the development of selective and safe drugs targeting ClC-1, with the aim to restore normal muscle function. This review summarizes the most relevant research on ClC-1 channel physiology, associated diseases, and pharmacology.
Collapse
Affiliation(s)
- Concetta Altamura
- Department of Biomedical Sciences and Human Oncology, School of Medicine, University of Bari "Aldo Moro", Bari, Italy
| | - Jean-Francois Desaphy
- Department of Biomedical Sciences and Human Oncology, School of Medicine, University of Bari "Aldo Moro", Bari, Italy
| | - Diana Conte
- Department of Pharmacy-Drug Sciences, University of Bari "Aldo Moro", Bari, Italy
| | - Annamaria De Luca
- Department of Pharmacy-Drug Sciences, University of Bari "Aldo Moro", Bari, Italy
| | - Paola Imbrici
- Department of Pharmacy-Drug Sciences, University of Bari "Aldo Moro", Bari, Italy.
| |
Collapse
|
2
|
Imbrici P, Altamura C, Pessia M, Mantegazza R, Desaphy JF, Camerino DC. ClC-1 chloride channels: state-of-the-art research and future challenges. Front Cell Neurosci 2015; 9:156. [PMID: 25964741 PMCID: PMC4410605 DOI: 10.3389/fncel.2015.00156] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2015] [Accepted: 04/08/2015] [Indexed: 01/06/2023] Open
Abstract
The voltage-dependent ClC-1 chloride channel belongs to the CLC channel/transporter family. It is a homodimer comprising two individual pores which can operate independently or simultaneously according to two gating modes, the fast and the slow gate of the channel. ClC-1 is preferentially expressed in the skeletal muscle fibers where the presence of an efficient Cl(-) homeostasis is crucial for the correct membrane repolarization and propagation of action potential. As a consequence, mutations in the CLCN1 gene cause dominant and recessive forms of myotonia congenita (MC), a rare skeletal muscle channelopathy caused by abnormal membrane excitation, and clinically characterized by muscle stiffness and various degrees of transitory weakness. Elucidation of the mechanistic link between the genetic defects and the disease pathogenesis is still incomplete and, at this time, there is no specific treatment for MC. Still controversial is the subcellular localization pattern of ClC-1 channels in skeletal muscle as well as its modulation by some intracellular factors. The expression of ClC-1 in other tissues such as in brain and heart and the possible assembly of ClC-1/ClC-2 heterodimers further expand the physiological properties of ClC-1 and its involvement in diseases. A recent de novo CLCN1 truncation mutation in a patient with generalized epilepsy indeed postulates an unexpected role of this channel in the control of neuronal network excitability. This review summarizes the most relevant and state-of-the-art research on ClC-1 chloride channels physiology and associated diseases.
Collapse
Affiliation(s)
- Paola Imbrici
- Department of Pharmacy - Drug Sciences, University of Bari “Aldo Moro”,Bari, Italy
| | - Concetta Altamura
- Department of Pharmacy - Drug Sciences, University of Bari “Aldo Moro”,Bari, Italy
| | - Mauro Pessia
- Department of Pharmacy - Drug Sciences, University of Bari “Aldo Moro”,Bari, Italy
| | - Renato Mantegazza
- Department of Pharmacy - Drug Sciences, University of Bari “Aldo Moro”,Bari, Italy
| | | | - Diana Conte Camerino
- Department of Pharmacy - Drug Sciences, University of Bari “Aldo Moro”,Bari, Italy
| |
Collapse
|
3
|
Yang B, Song JC, Jiang JH, Li ST. Receptor analysis of differential sensitivity change to succinylcholine induced by nerve injury in rat gastrocnemius. J Surg Res 2015; 195:136-43. [PMID: 25703161 DOI: 10.1016/j.jss.2015.01.012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2014] [Revised: 12/14/2014] [Accepted: 01/08/2015] [Indexed: 10/24/2022]
Abstract
BACKGROUND Urgent tracheal intubation is common in intensive care units and the emergency room, and succinylcholine is a first-line neuromuscular blocker used in these situations. Paraplegic or critically ill patients may be at a high risk of receiving succinylcholine because the denervation stage changes nicotinic receptors, which affect the efficacy and safety of succinylcholine. The objective of this study was to determine the receptor subtypes associated with changes in the pharmacodynamics of succinylcholine and its time-line trend. METHODS Denervated gastrocnemius was collected from tibial nerve transected rats. To determine the 50% effective dose of succinylcholine and rocuronium at 0 (control), 1, 3, 7, 14, and 28 d after denervation, action potential amplitude was monitored by an intracellular recording method. Subunits α1, α7, ε, and γ of the acetylcholine receptor (AChR) were quantified by real-time polymerase chain reaction. Receptor amount and pharmacodynamic changes were analyzed by correlation and regression analysis. RESULTS The pharmacodynamic change in succinylcholine was a dynamic process, and at the same time α7, ε, and γ-nicotinic AChR genes in denervated muscle were significantly changed but only α7 was closely correlated with the action of succinylcholine. Subunit γ and α7 were related to pharmacodynamic change in the nondepolarizing neuromuscular agent, rocuronium. CONCLUSIONS Nerve injury may alter nicotinic AChR subtypes in skeletal muscle at different stages, which probably affected the pharmacodynamics of neuromuscular blockers in different ways. Denervation time and stage and the type of neuromuscular blocker and dosage should be taken into consideration when using these drugs in patients with nerve injury.
Collapse
Affiliation(s)
- Bin Yang
- Department of Anesthesiology, Shanghai First People's Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, P.R.China
| | - Jin-Chao Song
- Department of Anesthesiology, Eastern Hepatobiliary Surgery Hospital, Second Military Medical University, Shanghai, China
| | - Ji-Hong Jiang
- Department of Anesthesiology, Shanghai First People's Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, P.R.China
| | - Shi-Tong Li
- Department of Anesthesiology, Shanghai First People's Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, P.R.China.
| |
Collapse
|
4
|
Yang B, Jiang JH, Zhou YC, Zhang Y, Li ST. Denervation stage differentially influences resistance to neuromuscular blockers in rat gastrocnemius. J Surg Res 2013; 180:266-73. [DOI: 10.1016/j.jss.2012.11.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2012] [Revised: 10/30/2012] [Accepted: 11/02/2012] [Indexed: 10/27/2022]
|
5
|
Leite-Moreira AF, Rocha-Sousa A, Henriques-Coelho T. Cardiac, skeletal, and smooth muscle regulation by ghrelin. VITAMINS AND HORMONES 2008; 77:207-38. [PMID: 17983858 DOI: 10.1016/s0083-6729(06)77009-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Ghrelin, mainly secreted from gastric mucosa, is the endogenous ligand for the growth hormone secretagogue receptor and induces a potent release of growth hormone. Ghrelin is widely expressed in different tissues and therefore has both endocrine and paracrine/autocrine effects. In this chapter, we summarize: (1) structure and distribution of ghrelin and its receptors; (2) myocardial effects of ghrelin, describing its acute and chronic actions on cardiac function; (3) ghrelin effects on smooth muscle, namely vascular smooth muscle, intraocular and gastrointestinal smooth muscle; and (4) skeletal actions of ghrelin. Ghrelin has a potent vasodilator effect, thereby reducing cardiac afterload and increasing cardiac output. In models of heart failure and myocardial ischemia, ghrelin administration has beneficial effects. At smooth muscle, ghrelin modulates vascular tone, increases gut transit, and relaxes iris muscles. In the skeletal muscle, ghrelin regulates resting membrane potential. In conclusion, there are increasing evidences that ghrelin is a peptide with paracrine actions that can modulate cardiac, smooth, and skeletal muscle functions.
Collapse
Affiliation(s)
- Adelino F Leite-Moreira
- Department of Physiology, Faculty of Medicine, University of Porto, Alameda Professor Hernâni Monteiro, 4200-319, Porto, Portugal
| | | | | |
Collapse
|
6
|
Fraysse B, Desaphy JF, Rolland JF, Pierno S, Liantonio A, Giannuzzi V, Camerino C, Didonna MP, Cocchi D, De Luca A, Conte Camerino D. Fiber type-related changes in rat skeletal muscle calcium homeostasis during aging and restoration by growth hormone. Neurobiol Dis 2006; 21:372-80. [PMID: 16153853 DOI: 10.1016/j.nbd.2005.07.012] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2005] [Accepted: 07/29/2005] [Indexed: 01/06/2023] Open
Abstract
The mechanisms by which aging induces muscle impairment are not well understood yet. We studied the impact of aging on Ca2+ homeostasis in the slow-twitch soleus and the fast-twitch extensor digitorum longus (EDL) muscles of aged rats by using the fura-2 fluorescent probe. In both muscles aging increases the resting cytosolic calcium concentration ([Ca2+]i). This effect was independent on calcium influx since a reduced resting permeability of sarcolemma to divalent cations was observed in aged muscles likely due to a reduced activity of leak channels. Importantly the effects of aging on resting [Ca2+]i, fiber diameter, mechanical threshold and sarcolemmal resting conductances were less pronounced in the soleus muscle, suggesting that muscle impairment may be less dependent on [Ca2+]i in the slow-twitch muscle. The treatment of aged rats with growth hormone restored the resting [Ca2+]i toward adult values in both muscles. Thus, an increase of resting [Ca2+]i may contribute to muscle weakness associated with aging and may be considered for developing new therapeutic strategies in the elderly.
Collapse
Affiliation(s)
- Bodvael Fraysse
- Division of Pharmacology, Department of Pharmaco-Biology, Faculty of Pharmacy, University of Bari, Bari I-70125, Italy
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
7
|
Pierno S, Luca AD, Desaphy JF, Fraysse B, Liantonio A, Didonna MP, Lograno M, Cocchi D, Smith RG, Camerino DC. Growth hormone secretagogues modulate the electrical and contractile properties of rat skeletal muscle through a ghrelin-specific receptor. Br J Pharmacol 2003; 139:575-84. [PMID: 12788817 PMCID: PMC1573883 DOI: 10.1038/sj.bjp.0705284] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
(1) Growth hormone secretagogues (GHS) exhibit potent growth hormone (GH)-releasing activity through the activation of a pituitary receptor. Here, we consider the possibility that GHS can target a specific receptor in rat skeletal muscle and have a role in the control of muscle function. (2) By means of the intracellular microelectrode technique, we found that in vitro application of hexarelin and L-163,255 dose dependently reduced resting chloride (gCl) and potassium (gK) conductances in rat skeletal muscle. These effects were prevented by the GHS-receptor antagonist [D-Lys-3]-GHRP-6, and by either phospholipase C or protein kinase C (PKC) inhibitors. Ghrelin, a natural ligand of GHS receptors, also induced a reduction of muscle gCl and gK, which was antagonised by [D-Lys-3]-GHRP-6. (3) Both GHS shifted the mechanical threshold for the contraction of muscle fibres towards more negative voltages. Accordingly, by means of FURA-2 fluorescent measurements, we demonstrated that L-163,255 induced a resting [Ca(2+)](i) increase, which was reversible and not blocked by nifedipine or removal of external Ca(2+). (4) Ageing is a condition characterised by a deficit of GH secretion, which in turn modifies the electrical and contractile properties of skeletal muscle. In contrast to GH, chronic treatment of aged rats with hexarelin or L-163,255 failed to restore the electrical and contractile muscle properties. Moreover, the two GHS applied in vitro were able to antagonise the beneficial effect on gCl and gK obtained through chronic treatment of aged animals with GH. (5) Thus, skeletal muscle expresses a specific GHS receptor able to decrease gCl and gK through a PKC-mediated intracellular pathway. This peripheral action may account for the lack of restoration of skeletal muscle function in long-term GHS-treated aged animals.
Collapse
Affiliation(s)
- Sabata Pierno
- Unit of Pharmacology, Department of Pharmacobiology, Faculty of Pharmacy, University of Bari, Italy
| | - Annamaria De Luca
- Unit of Pharmacology, Department of Pharmacobiology, Faculty of Pharmacy, University of Bari, Italy
| | - Jean-François Desaphy
- Unit of Pharmacology, Department of Pharmacobiology, Faculty of Pharmacy, University of Bari, Italy
| | - Bodvael Fraysse
- Unit of Pharmacology, Department of Pharmacobiology, Faculty of Pharmacy, University of Bari, Italy
| | - Antonella Liantonio
- Unit of Pharmacology, Department of Pharmacobiology, Faculty of Pharmacy, University of Bari, Italy
| | - Maria Paola Didonna
- Unit of Pharmacology, Department of Pharmacobiology, Faculty of Pharmacy, University of Bari, Italy
| | - Marcello Lograno
- Unit of Pharmacology, Department of Pharmacobiology, Faculty of Pharmacy, University of Bari, Italy
| | - Daniela Cocchi
- Department of Biomedical Sciences and Biotechnology, University of Brescia, Italy
| | - Roy G Smith
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, U.S.A
| | - Diana Conte Camerino
- Unit of Pharmacology, Department of Pharmacobiology, Faculty of Pharmacy, University of Bari, Italy
- Author for correspondence:
| |
Collapse
|
8
|
Abstract
Between the ages of 20 and 80, humans lose approximately 20-30% of their skeletal muscle mass. This age-related loss of muscle mass, sometimes described as 'sarcopenia of old age', is the consequence of complicated multifactorial processes and is commonly associated with osteopenia or osteoporosis. Consequences of the aging changes in muscle are declining physiological function and loss of muscle strength, typically associated with reduced physical activities. Consequently, falls and subsequent serious injuries are prevalent in the elderly. Thus, it is imperative to try and understand the processes, leading to age-related muscle loss, in order to develop means to retard this phenomenon leading to improved quality of life in the elderly. It is possible to divide the causes of muscle aging to intrinsic factors, involving changes at the molecular and cellular levels, and to extrinsic or environmental factors. The purpose of this review is to describe some of the biochemical processes and the possible mechanisms of muscle aging and to evaluate the importance of various extrinsic factors such as nutrition, exercise and limb immobilization. Changes in the aging skeletal muscle are reviewed with regard to: (a) enzyme activities, protein turnover and repair capacities (b) mitochondrial functioning and energy reserve systems (c) ion content and regulation (d) oxidative stress and free radicals (e) nutrition and caloric restriction (f) exercise and limb immobilization.
Collapse
Affiliation(s)
- Eli Carmeli
- Sackler Faculty of Medicine, Department of Physical Therapy, Tel Aviv University, Ramat Aviv, Israel
| | | | | |
Collapse
|
9
|
Singleton JR, Feldman EL. Insulin-like growth factor-I in muscle metabolism and myotherapies. Neurobiol Dis 2001; 8:541-54. [PMID: 11493020 DOI: 10.1006/nbdi.2001.0416] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The critical anabolic and trophic role of signaling by insulin-like growth factors (IGF) I and II via the type-I IGF receptor (IGF-IR) is reviewed throughout the life of skeletal myocytes. The proliferative effects of IGF-IR stimulation, both during embryogenesis and during satellite cell proliferation following denervation or muscle injury, are mediated primarily through activation of mitogen-activated protein kinases. Signaling through phosphatidylinositol 3-kinase is essential to muscle protein synthesis and glucose uptake and may contribute to the observed resilience of mature muscle to programmed cell death. Degeneration or inhibition of the GH--IGF-I axis by aging, cachexia, sepsis, diabetes, drugs, and disuse all enhance muscle catabolism, and opposition of these effects by IGF-I may form the basis of effective myotherapy.
Collapse
Affiliation(s)
- J R Singleton
- Department of Neurology, University of Utah, Salt Lake City, Utah 84108, USA.
| | | |
Collapse
|
10
|
Herzig S, Neumann J. Effects of serine/threonine protein phosphatases on ion channels in excitable membranes. Physiol Rev 2000; 80:173-210. [PMID: 10617768 DOI: 10.1152/physrev.2000.80.1.173] [Citation(s) in RCA: 202] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This review deals with the influence of serine/threonine-specific protein phosphatases on the function of ion channels in the plasma membrane of excitable tissues. Particular focus is given to developments of the past decade. Most of the electrophysiological experiments have been performed with protein phosphatase inhibitors. Therefore, a synopsis is required incorporating issues from biochemistry, pharmacology, and electrophysiology. First, we summarize the structural and biochemical properties of protein phosphatase (types 1, 2A, 2B, 2C, and 3-7) catalytic subunits and their regulatory subunits. Then the available pharmacological tools (protein inhibitors, nonprotein inhibitors, and activators) are introduced. The use of these inhibitors is discussed based on their biochemical selectivity and a number of methodological caveats. The next section reviews the effects of these tools on various classes of ion channels (i.e., voltage-gated Ca(2+) and Na(+) channels, various K(+) channels, ligand-gated channels, and anion channels). We delineate in which cases a direct interaction between a protein phosphatase and a given channel has been proven and where a more complex regulation is likely involved. Finally, we present ideas for future research and possible pathophysiological implications.
Collapse
Affiliation(s)
- S Herzig
- Institut für Pharmakologie, Universität Köln, Köln, Germany.
| | | |
Collapse
|
11
|
Pierno S, De Luca A, Beck CL, George AL, Conte Camerino D. Aging-associated down-regulation of ClC-1 expression in skeletal muscle: phenotypic-independent relation to the decrease of chloride conductance. FEBS Lett 1999; 449:12-6. [PMID: 10225418 DOI: 10.1016/s0014-5793(99)00202-1] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
In order to clarify the mechanism underlying the reduction of resting membrane chloride conductance (gCl) during aging, the levels of mRNA encoding the principal skeletal muscle chloride channel, ClC-1, were measured. Total RNA samples isolated from tibialis anterior muscles of aged (24-29 months old) and adult (3-4 months old) rats were examined for ClC-1 expression using Northern blot analysis, and macroscopic gCl was recorded from extensor digitorum longus muscle fibers from each adult and aged rat in vitro using a two intracellular microelectrode technique. Although interindividual variability was observed, aged rats exhibited a parallel reduction of both gCl and ClC-1 mRNA expression as compared to adult rats. A linear correlation exists between individual values of ClC-1 mRNA and gCl. These results provide evidence that ClC-1 is the main determinant of sarcolemmal gCl and demonstrate that the decrease of gCl observed during aging is associated with a down-regulation of ClC-1 expression in muscle.
Collapse
Affiliation(s)
- S Pierno
- Department of Pharmacobiology, Faculty of Pharmacy, University of Bari, Italy
| | | | | | | | | |
Collapse
|
12
|
De Luca A, Pierno S, Camerino C, Cocchi D, Camerino DC. Higher content of insulin-like growth factor-I in dystrophic mdx mouse: potential role in the spontaneous regeneration through an electrophysiological investigation of muscle function. Neuromuscul Disord 1999; 9:11-8. [PMID: 10063830 DOI: 10.1016/s0960-8966(98)00092-3] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Insulin-like growth factor-I (IGF-I) is known to promote proliferation and differentiation of muscle cells during growth and regeneration. Both these conditions are characterized by acquisition of specialized muscle functions, such as a large macroscopic chloride conductance (GCl), a parameter that is a target of growth hormone (GH)/IGF-I axis action on skeletal muscle. The present study has been aimed at evaluating the role of IGF-I in the spontaneous regeneration occurring in hind limb muscle of dystrophic mdx mouse. IGF-I levels have been measured in hind limb muscles, plasma and liver of mdx and control mice of 8-10 weeks and 5 months of age by radioimmunoassay. In parallel the biophysical and pharmacological properties of muscle chloride channels of extensor digitorum longus (EDL) muscle fibers of mice belonging to the same age-group have been measured electrophysiologically in vitro. At 8-10 weeks of age, significantly greater amounts of IGF-I were found in plasma and hind limb muscles of mdx mice with respect to controls. Such a difference was only just detectable and no longer statistically significant at 5 months of age. No differences were found in hepatic IGF-I levels at either age. The EDL muscle fibers of mdx mice at 8-10 weeks of age were characterized by higher GCl values and by a different pharmacological sensitivity to the enantiomers of 2-(p-chlorophenoxy)-propionic acid (CPP), specific chloride channel ligands, with respect to age-matched controls. However, these differences were no longer detected at 5 months of age. Our results suggest a role of IGF-I in the high regenerative potential of muscles from mdx mice and support the hypothesis that the biophysical and pharmacological properties of chloride channels of EDL muscle fibers are sensitive indices of the action of regeneration-promoting factors on muscle function.
Collapse
Affiliation(s)
- A De Luca
- Unità di Farmacologia, Dipartimento Farmacobiologico, Facoltà di Farmacia, Università di Bari, Italy
| | | | | | | | | |
Collapse
|
13
|
De Luca A, Pierno S, Liantonio A, Camerino C, Conte Camerino D. Phosphorylation and IGF-1-mediated dephosphorylation pathways control the activity and the pharmacological properties of skeletal muscle chloride channels. Br J Pharmacol 1998; 125:477-82. [PMID: 9806330 PMCID: PMC1565652 DOI: 10.1038/sj.bjp.0702107] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. In the present study we tested the hypothesis that insulin-like growth factor-1 (IGF-1) modulates resting chloride conductance (G(Cl)) of rat skeletal muscle by activating a phosphatase and that the chloride channel, based on the activity of phosphorylating-dephosphorylating pathways, has different sensitivity to specific ligands, such as the enantiomers of 2-(p-chlorophenoxy) propionic acid (CPP). 2. For this purpose G(Cl) in EDL muscle isolated from adult rat was first lowered by treatment with 5 nM 4-beta-phorbol 12,13 dibutyrate (4-beta-PDB), presumably activating protein kinase C (PKC). The effects of IGF-1 and of the enantiomers of CPP on G(Cl) were then tested. 3. IGF-1 (3.3 nM) had no effect of G(Cl) on EDL muscle fibres in normal physiological solution, whereas it completely counteracted the 30% decrease of G(Cl) induced by 4-beta-PDB. No effects of IGF-1 were observed on G(Cl) lowered by the phosphatase inhibitor okadaic acid (0.25 microM). 4. Ceramide, reported to activate on okadaic acid-sensitive phosphatase, mimicked the effects of IGF-1. In fact, N-acetyl-sphingosine (2.5-5 microM), not very effective in control conditions, increased the G(Cl) lowered by the phorbol ester, but not the G(Cl) lowered by okadaic acid. 5. In the presence of 4-beta-PDB, G(Cl) was differently affected by the enantiomers of CPP. The S(-)-CPP was remarkably less potent in producing the concentration-dependent reduction of G(Cl), whereas the R(+)-CPP caused an increase of G(Cl) at all the concentrations tested. 6. In conclusion, the PKC-induced lowering of G(Cl) is counteracted by IGF-1 through an okadaic acid sensitive phosphatase, and this effect can have therapeutic relevance in situations characterized by excessive channel phosphorylation. In turn the phosphorylation state of the channel can modulate the effects and the therapeutic potential of direct channel ligands.
Collapse
Affiliation(s)
- A De Luca
- Dipartimento Farmacobiologico, Facoltà di Farmacia, Università di Bari, Italy
| | | | | | | | | |
Collapse
|