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González Sanabria J, Hurtado Paso M, Frontera T, Losavio A. Effect of endogenous purines on electrically evoked ACh release at the mouse neuromuscular junction. J Neurosci Res 2022; 100:1933-1950. [PMID: 35839285 DOI: 10.1002/jnr.25107] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2021] [Revised: 06/22/2022] [Accepted: 07/04/2022] [Indexed: 11/11/2022]
Abstract
At the mouse neuromuscular junction, adenosine triphosphate (ATP), which is co-released with the neurotransmitter acetylcholine (ACh), and its metabolite adenosine, modulate neurotransmitter release by activating presynaptic inhibitory P2Y13 receptors (a subtype of ATP/adenosine diphosphate [ADP] receptor), inhibitory A1 and A3 adenosine receptors, and excitatory A2A adenosine receptors. To study the effect of endogenous purines, when phrenic-diaphragm preparations are depolarized by different nerve stimulation patterns, we analyzed the effect of the antagonists for P2Y13 , A1 , A3 , and A2A receptors (AR-C69931MX, 8-cyclopentyl-1,3-dipropylxanthine, MRS-1191, and SCH-58261, respectively) on the amplitude of the end-plate potentials of the trains, and contrasted these results with those obtained with the selective agonists of these receptors (2-methylthioadenosine 5'-diphosphate trisodium salt hydrate, 2-chloro-N6 -cyclopentyl-adenosine, inosine, and PSB-0777, respectively). During continuous 0.5-Hz stimulation, the amount of endogenous purines was not enough to activate purinergic receptors, while at continuous 5-Hz stimulation, an incipient action of endogenous purines on P2Y13 , A1 and A3 receptors might be evident just at the end of the trains. During continuous 50-Hz stimulation, the concentration of endogenous ATP/ADP and adenosine exerted an inhibitory action on ACh release after of the initial phase of the train, but when the nerve was stimulated at intermittent 50 Hz (5 bursts), this behavior was not observed. Excitatory A2A receptors were only activated when continuous 100-Hz stimulation was applied. In conclusion, when motor nerve terminals are depolarized by repetitive stimulation of the phrenic nerve, endogenous ATP/ADP and adenosine are able to fine-tune neurosecretion depending on the frequency and pattern of stimulation.
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Affiliation(s)
- Javier González Sanabria
- Laboratorio de Neurofisiología, Instituto de Investigaciones Médicas Alfredo Lanari - Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad de Buenos Aires (UBA), Ciudad Autónoma de Buenos Aires, Argentina
| | - Maximiliano Hurtado Paso
- Laboratorio de Neurofisiología, Instituto de Investigaciones Médicas Alfredo Lanari - Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad de Buenos Aires (UBA), Ciudad Autónoma de Buenos Aires, Argentina
| | - Tamara Frontera
- Laboratorio de Neurofisiología, Instituto de Investigaciones Médicas Alfredo Lanari - Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad de Buenos Aires (UBA), Ciudad Autónoma de Buenos Aires, Argentina
| | - Adriana Losavio
- Laboratorio de Neurofisiología, Instituto de Investigaciones Médicas Alfredo Lanari - Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad de Buenos Aires (UBA), Ciudad Autónoma de Buenos Aires, Argentina
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Mechanism of P2X7 receptor-dependent enhancement of neuromuscular transmission in pannexin 1 knockout mice. Purinergic Signal 2018; 14:459-469. [PMID: 30362043 DOI: 10.1007/s11302-018-9630-7] [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: 07/05/2018] [Accepted: 10/02/2018] [Indexed: 01/15/2023] Open
Abstract
P2X7 receptors are present in presynaptic membranes of motor synapses, but their regulatory role in modulation of neurotransmitter release remains poorly understood. P2X7 receptors may interact with pannexin 1 channels to form a purinergic signaling unit. The potential mechanism of P2X7 receptor-dependent modulation of acetylcholine (ACh) release was investigated by recording miniature endplate potentials (MEPPs) and evoked endplate potentials (EPPs) in neuromuscular junctions of wild-type (WT) and pannexin 1 knockout (Panx1-/-) mice. Modulation of P2X7 receptors with the selective inhibitor A740003 or the selective agonist BzATP did not alter the parameters of either spontaneous or evoked ACh release in WT mice. In Panx1-/- mice, BzATP-induced activation of P2X7 receptors resulted in a uniformly increased quantal content of EPPs during a short stimulation train. This effect was accompanied by an increase in the size of the readily releasable pool, while the release probability did not change. Inhibition of calmodulin by W-7 or of calcium/calmodulin-dependent kinase II (CaMKII) by KN-93 completely prevented the potentiating effect of BzATP on the EPP quantal content. The blockade of L-type calcium channels also prevented BzATP action on evoked synaptic activity. Thus, the activation of presynaptic P2X7 receptors in mice lacking pannexin 1 resulted in enhanced evoked ACh release. Such enhanced release was provoked by triggering the calmodulin- and CaMKII-dependent signaling pathway, followed by activation of presynaptic L-type calcium channels. We suggest that in WT mice, this pathway is downregulated due to pannexin 1-dependent tonic activation of inhibitory presynaptic purinergic receptors, which overcomes P2X7-mediated effects.
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Zhang D, Wang D, Pipinos II, Muelleman RL, Li YL. Dexamethasone promotes long-term functional recovery of neuromuscular junction in a murine model of tourniquet-induced ischaemia-reperfusion. Acta Physiol (Oxf) 2017; 219:453-464. [PMID: 27306588 DOI: 10.1111/apha.12737] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Revised: 03/12/2016] [Accepted: 06/14/2016] [Indexed: 11/28/2022]
Abstract
AIM Tourniquet-induced ischaemia and subsequent reperfusion cause serious ischaemia-reperfusion (IR) injury in the neuromuscular junction (NMJ) and skeletal muscle. Here, we investigated whether dexamethasone (Dex) promotes long-term functional recovery of the NMJ and skeletal muscle in tourniquet-induced hindlimb IR. METHODS Unilateral hindlimb of C57/BL6 mice was subjected to 3 h of ischaemia following 6 weeks of reperfusion (6-wk IR). Dex treatment began on the day of IR induction and lasted for different periods. Sciatic nerve-stimulated gastrocnemius muscle contraction was detected in situ. Function of the NMJ was measured in situ using electrophysiological recording of the miniature endplate potential (mEPP) and endplate potential (EPP). Western blot was used to detect protein expression of nicotinic acetylcholine receptors (nAChRs) in gastrocnemius muscles. RESULTS Gastrocnemius muscle contraction in mice with 6-wk IR was about 60% of normal skeletal muscle contraction recorded in age-matched sham mice. The amplitude of the mEPP and EPP was lower in mice with 6-wk IR, compared to sham mice. Dex treatment for 1 or 3 days did not restore the function of the NMJ and improve gastrocnemius muscle contraction in mice with 6-wk IR. Dex treatment for 1 week exerted a maximum effect on improving the function of the NMJ and skeletal muscle, with the effect of Dex gradually lessening with prolonged Dex treatment. There are no significant differences in protein expression of nAChR-α1 and nAChR-β1 subunits in the gastrocnemius muscle among all groups. CONCLUSION Dex promotes repair of the NMJ and subsequently restores skeletal muscle contractile function in tourniquet-induced 6-wk IR.
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Affiliation(s)
- D. Zhang
- Department of Emergency Medicine; University of Nebraska Medical Center; Omaha NE USA
| | - D. Wang
- Department of Pharmaceutical Sciences; University of Nebraska Medical Center; Omaha NE USA
| | - I. I. Pipinos
- Department of Surgery; University of Nebraska Medical Center; Omaha NE USA
| | - R. L. Muelleman
- Department of Emergency Medicine; University of Nebraska Medical Center; Omaha NE USA
| | - Y.-L. Li
- Department of Emergency Medicine; University of Nebraska Medical Center; Omaha NE USA
- Department of Cellular & Integrative Physiology; University of Nebraska Medical Center; Omaha NE USA
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Heredia DJ, Schubert D, Maligireddy S, Hennig GW, Gould TW. A Novel Striated Muscle-Specific Myosin-Blocking Drug for the Study of Neuromuscular Physiology. Front Cell Neurosci 2016; 10:276. [PMID: 27990107 PMCID: PMC5130989 DOI: 10.3389/fncel.2016.00276] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2016] [Accepted: 11/18/2016] [Indexed: 12/27/2022] Open
Abstract
The failure to transmit neural action potentials (APs) into muscle APs is referred to as neuromuscular transmission failure (NTF). Although synaptic dysfunction occurs in a variety of neuromuscular diseases and impaired neurotransmission contributes to muscle fatigue, direct evaluation of neurotransmission by measurement of successfully transduced muscle APs is difficult due to the subsequent movements produced by muscle. Moreover, the voltage-gated sodium channel inhibitor used to study neurotransmitter release at the adult neuromuscular junction is ineffective in embryonic tissue, making it nearly impossible to precisely measure any aspect of neurotransmission in embryonic lethal mouse mutants. In this study we utilized 3-(N-butylethanimidoyl)-4-hydroxy-2H-chromen-2-one (BHC), previously identified in a small-molecule screen of skeletal muscle myosin inhibitors, to suppress movements without affecting membrane currents. In contrast to previously characterized drugs from this screen such as N-benzyl-p-toluene sulphonamide (BTS), which inhibit skeletal muscle myosin ATPase activity but also block neurotransmission, BHC selectively blocked nerve-evoked muscle contraction without affecting neurotransmitter release. This feature allowed a detailed characterization of neurotransmission in both embryonic and adult mice. In the presence of BHC, neural APs produced by tonic stimulation of the phrenic nerve at rates up to 20 Hz were successfully transmitted into muscle APs. At higher rates of phrenic nerve stimulation, NTF was observed. NTF was intermittent and characterized by successful muscle APs following failed ones, with the percentage of successfully transmitted muscle APs diminishing over time. Nerve stimulation rates that failed to produce NTF in the presence of BHC similarly failed to produce a loss of peak muscle fiber shortening, which was examined using a novel optical method of muscle fatigue, or a loss of peak cytosolic calcium transient intensity, examined in whole populations of muscle cells expressing the genetically-encoded calcium indicator GCaMP3. Most importantly, BHC allowed for the first time a detailed analysis of synaptic transmission, calcium signaling and fatigue in embryonic mice, such as in Vamp2 mutants reported here, that die before or at birth. Together, these studies illustrate the wide utility of BHC in allowing stable measurements of neuromuscular function.
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Affiliation(s)
- Dante J Heredia
- Department of Physiology and Cell Biology, University of Nevada School of Medicine Reno, NV, USA
| | - Douglas Schubert
- Department of Physiology and Cell Biology, University of Nevada School of Medicine Reno, NV, USA
| | - Siddhardha Maligireddy
- Department of Physiology and Cell Biology, University of Nevada School of Medicine Reno, NV, USA
| | - Grant W Hennig
- Department of Physiology and Cell Biology, University of Nevada School of Medicine Reno, NV, USA
| | - Thomas W Gould
- Department of Physiology and Cell Biology, University of Nevada School of Medicine Reno, NV, USA
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Scurry AN, Heredia DJ, Feng CY, Gephart GB, Hennig GW, Gould TW. Structural and Functional Abnormalities of the Neuromuscular Junction in the Trembler-J Homozygote Mouse Model of Congenital Hypomyelinating Neuropathy. J Neuropathol Exp Neurol 2016; 75:334-46. [PMID: 26921370 DOI: 10.1093/jnen/nlw004] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Mutations in peripheral myelin protein 22 (PMP22) result in the most common form of Charcot-Marie-Tooth (CMT) disease, CMT1A. This hereditary peripheral neuropathy is characterized by dysmyelination of peripheral nerves, reduced nerve conduction velocity, and muscle weakness. APMP22 point mutation in L16P (leucine 16 to proline) underlies a form of human CMT1A as well as the Trembler-J mouse model of CMT1A. Homozygote Trembler-J mice (Tr(J)) die early postnatally, fail to make peripheral myelin, and, therefore, are more similar to patients with congenital hypomyelinating neuropathy than those with CMT1A. Because recent studies of inherited neuropathies in humans and mice have demonstrated that dysfunction and degeneration of neuromuscular synapses or junctions (NMJs) often precede impairments in axonal conduction, we examined the structure and function of NMJs in Tr(J)mice. Although synapses appeared to be normally innervated even in end-stage Tr(J)mice, the growth and maturation of the NMJs were altered. In addition, the amplitudes of nerve-evoked muscle endplate potentials were reduced and there was transmission failure during sustained nerve stimulation. These results suggest that the severe congenital hypomyelinating neuropathy that characterizes Tr(J)mice results in structural and functional deficits of the developing NMJ.
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Affiliation(s)
- Alexandra N Scurry
- From the Departments of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada
| | - Dante J Heredia
- From the Departments of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada
| | - Cheng-Yuan Feng
- From the Departments of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada
| | - Gregory B Gephart
- From the Departments of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada
| | - Grant W Hennig
- From the Departments of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada
| | - Thomas W Gould
- From the Departments of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada.
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Li J, Liu YQ, Zhang HT. Effects of rocuronium and vecuronium on initial rundown of endplate potentials in the isolated phrenic nerve diaphragm preparation of rats. SPRINGERPLUS 2013; 2:155. [PMID: 23641322 PMCID: PMC3639353 DOI: 10.1186/2193-1801-2-155] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/23/2012] [Accepted: 04/04/2013] [Indexed: 11/18/2022]
Abstract
Rocuronium and vecuronium, two non-depolarizing neuromuscular blockers, have been widely used in surgery procedures. However, their electrophysiological properties need to be more widely explored. We examined the effects of rocuronium and vecuronium on initial rundown of endplate potential amplitudes in the non-uniform stretched muscle preparation of the rat isolated phrenic nerve diaphragm. More specifically, the endplate potentials were recorded with one microelectrode from a single endplate. The effects of rocuronium or vecuronium each at 4 concentrations (0.5 ×, l ×, 2 ×, 4 × EC95; EC95 = concentration of the drug required to produce the inhibitory effect by 95%) on the amplitude of endplate potentials and its rundown were observed. Treatment of the isolated rat phrenic nerve-diaphragm preparation with rocuronium (2.5-20 μg/ml) or vecuronium (0.5-4 μg/ml) decreased the amplitude of endplate potentials and inhibited its rundown in a concentration-dependent manner. At the concentration (2.5 μg/ml for rocuronium and 0.5 μg/ml for vecuronium) that did not alter the endplate potential amplitude, the onset of reduced endplate potential rundown was 3 and 5 min after administration of rocuronium or vecuronium, respectively. The results suggest that rocuronium and vecuronium block the neuromuscular junction presynaptically and that rocuronium does it faster than vecuronium.
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Affiliation(s)
- Jun Li
- Department of Anesthesiology, Navy General Hospital of PLA, Beijing, 100037 China
| | - Yong-Qin Liu
- Department of Anesthesiology, Navy General Hospital of PLA, Beijing, 100037 China
| | - Han-Ting Zhang
- Departments of Behavioral Medicine & Psychiatry and Physiology & Pharmacology, West Virginia University Health Sciences Center, Morgantown, WV 26506 USA
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Role of acetylcholinesterase on the structure and function of cholinergic synapses: insights gained from studies on knockout mice. Cell Mol Neurobiol 2011; 31:909-20. [PMID: 21538119 DOI: 10.1007/s10571-011-9690-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2011] [Accepted: 04/06/2011] [Indexed: 10/18/2022]
Abstract
Electrophysiological and ultrastructural studies were performed on phrenic nerve-hemidiaphragm preparations isolated from wild-type and acetylcholinesterase (AChE) knockout (KO) mice to determine the compensatory mechanisms manifested by the neuromuscular junction to excess acetylcholine (ACh). The diaphragm was selected since it is the primary muscle of respiration, and it must adapt to allow for survival of the organism in the absence of AChE. Nerve-elicited muscle contractions, miniature endplate potentials (MEPPs) and evoked endplate potentials (EPPs) were recorded by conventional electrophysiological techniques from phrenic nerve-hemidiaphragm preparations isolated from 1.5- to 2-month-old wild-type (AChE(+/+)) or AChE KO (AChE(-/-)) mice. These recordings were chosen to provide a comprehensive assessment of functional alterations of the diaphragm muscle resulting from the absence of AChE. Tension measurements from AChE(-/-) mice revealed that the amplitude of twitch tensions was potentiated, but tetanic tensions underwent a use-dependent decline at frequencies below 70 Hz and above 100 Hz. MEPPs recorded from hemidiaphragms of AChE(-/-) mice showed a reduction in frequency and a prolongation in decay (37%) but no change in amplitude compared to values observed in age-matched wild-type littermates. In contrast, MEPPs recorded from hemidiaphragms of wild-type mice that were exposed for 30 min to the selective AChE inhibitor 5-bis(4-allyldimethyl-ammoniumphenyl)pentane-3-one (BW284C51) exhibited a pronounced increase in amplitude (42%) and a more marked prolongation in decay (76%). The difference between MEPP amplitudes and decays in AChE(-/-) hemidiaphragms and in wild-type hemidiaphragms treated with BW284C51 represents effective adaptation by the former to a high ACh environment. Electron microscopic examination revealed that diaphragm muscles of AChE(-/-) mice had smaller nerve terminals and diminished pre- and post-synaptic surface contacts relative to neuromuscular junctions of AChE(+/+) mice. The morphological changes are suggested to account, in part, for the ability of muscle from AChE(-/-) mice to function in the complete absence of AChE.
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Wu ZZ, Li DP, Chen SR, Pan HL. Aminopyridines potentiate synaptic and neuromuscular transmission by targeting the voltage-activated calcium channel beta subunit. J Biol Chem 2009; 284:36453-36461. [PMID: 19850918 DOI: 10.1074/jbc.m109.075523] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Aminopyridines such as 4-aminopyridine (4-AP) are widely used as voltage-activated K(+) (Kv) channel blockers and can improve neuromuscular function in patients with spinal cord injury, myasthenia gravis, or multiple sclerosis. Here, we present novel evidence that 4-AP and several of its analogs directly stimulate high voltage-activated Ca(2+) channels (HVACCs) in acutely dissociated neurons. 4-AP, 4-(aminomethyl)pyridine, 4-(methylamino)pyridine, and 4-di(methylamino)pyridine profoundly increased HVACC, but not T-type, currents in dissociated neurons from the rat dorsal root ganglion, superior cervical ganglion, and hippocampus. The widely used Kv channel blockers, including tetraethylammonium, alpha-dendrotoxin, phrixotoxin-2, and BDS-I, did not mimic or alter the effect of 4-AP on HVACCs. In HEK293 cells expressing various combinations of N-type (Cav2.2) channel subunits, 4-AP potentiated Ca(2+) currents primarily through the intracellular beta(3) subunit. In contrast, 4-AP had no effect on Cav3.2 channels expressed in HEK293 cells. Furthermore, blocking Kv channels did not mimic or change the potentiating effects of 4-AP on neurotransmitter release from sensory and motor nerve terminals. Thus, our findings challenge the conventional view that 4-AP facilitates synaptic and neuromuscular transmission by blocking Kv channels. Aminopyridines can directly target presynaptic HVACCs to potentiate neurotransmitter release independent of Kv channels.
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Affiliation(s)
- Zi-Zhen Wu
- Division of Anesthesiology and Critical Care, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030
| | - De-Pei Li
- Division of Anesthesiology and Critical Care, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030
| | - Shao-Rui Chen
- Division of Anesthesiology and Critical Care, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030
| | - Hui-Lin Pan
- Division of Anesthesiology and Critical Care, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030; Program in Neuroscience, The University of Texas Graduate School of Biomedical Sciences, Houston, Texas 77225.
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Petrov KA, Kovyazina IV, Zobov VV, Bukharaeva EA, Reznik VS, Nikolsky EE. Effect of a tetraalkylammonium derivative of 6-methyluracil from a new class of acetylcholinesterase inhibitors on the endplate potential amplitude in muscles of different function types under high-frequency nerve stimulation. DOKLADY BIOLOGICAL SCIENCES : PROCEEDINGS OF THE ACADEMY OF SCIENCES OF THE USSR, BIOLOGICAL SCIENCES SECTIONS 2007; 415:261-264. [PMID: 17929660 DOI: 10.1134/s0012496607040035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Affiliation(s)
- K A Petrov
- Arbuzov Institute of Organic and Physical Chemistry, Kazan Research Center, Russian Academy of Sciences, ul. Akademika Arbuzova 8, Kazan, 420088 Tatarstan, Russia
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van Lunteren E, Moyer M. Modulation of biphasic rate of end-plate potential recovery in rat diaphragm. Muscle Nerve 2005; 31:321-30. [PMID: 15654692 DOI: 10.1002/mus.20245] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Previous diaphragm studies found that during intermittent stimulation, intratrain end-plate potential (EPP) amplitude rundown is accelerated by increasing stimulation frequency, whereas intertrain EPP rundown is independent of frequency. We hypothesized that increasing stimulation frequency accelerates rundown recovery, and with a biphasic time course. Intracellular recordings were made in vitro from rat phrenic nerve-hemidiaphragm preparations. EPP amplitude recovery after a 100-ms stimulation train and 100 ms of quiescence was significantly greater following stimulation at 200 HZ than at 20-100 HZ, despite larger antecedent EPP decline. EPP amplitudes recovered with a biphasic pattern: an early component with a fast time-constant (0.03-0.06 s) and a late component with a slow time-constant (0.5-5 s). Increased antecedent stimulation frequency accelerated the early component, but stimulation duration or pulse number modulated the late component. When interpreted in the context of vesicle recycling and replenishment models involving multiple pools and pathways, these data suggest that antecedent stimulation frequency regulates predominantly the fast pathways. This may have important implications for the development of respiratory failure in diseases of the neuromuscular junction, such as myasthenia gravis, when the firing duration and frequency are altered in association with changes in breathing pattern.
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Affiliation(s)
- Erik van Lunteren
- Department of Medicine, Cleveland Department of Veterans Affairs Medical Center, Case Western Reserve University, Cleveland, Ohio 44106, USA.
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Desaulniers P, Lavoie PA, Gardiner PF. Effect of rat soleus muscle overload on neuromuscular transmission efficacy during continuous and intermittent activation. Exp Physiol 2005; 90:333-40. [PMID: 15640276 DOI: 10.1113/expphysiol.2004.029132] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Increased neuromuscular activity is known to provoke morphological and functional adaptations at the neuromuscular synapse. Most of these changes have been documented following endurance exercise training programmes. In this study, the effect of rat soleus muscle overload produced by tenotomy plus voluntary wheel-cage activity on neuromuscular transmission efficacy was investigated. The overload protocol increased miniature endplate potential (MEPP) and endplate potential (EPP) amplitudes by 17 and 19%, respectively (both P < 0.01), and increased MEPP frequency by 86% (P < 0.01). EPP amplitude rundown during continuous trains of activation was attenuated by approximately 10% in the overloaded group (P < 0.01). Also, during intermittent activation, the overload protocol attenuated EPP amplitude rundown, mainly by enhancing EPP amplitude recovery by approximately 10% during the quiescent periods (P < 0.01). Although the present results show that both the degree and direction of adaptation are similar to what has been observed at rat soleus neuromuscular junctions following an endurance training protocol, there are important nuances between the results, suggesting different mechanisms through which these changes may occur.
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Oliveira L, Timóteo MA, Correia-de-Sá P. Tetanic depression is overcome by tonic adenosine A(2A) receptor facilitation of L-type Ca(2+) influx into rat motor nerve terminals. J Physiol 2004; 560:157-68. [PMID: 15297571 PMCID: PMC1665215 DOI: 10.1113/jphysiol.2004.067595] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2004] [Accepted: 08/04/2004] [Indexed: 12/16/2022] Open
Abstract
Motor nerve terminals possess multiple voltage-sensitive calcium channels operating acetylcholine (ACh) release. In this study, we investigated whether facilitation of neuromuscular transmission by adenosine generated during neuronal firing was operated by Ca(2+) influx via 'prevalent' P-type or via the recruitment of 'silent' L-type channels. The release of [(3)H]ACh from rat phrenic nerve endings decreased upon increasing the stimulation frequency of the trains (750 pulses) from 5 Hz (83 +/- 4 x 10(3) disintegrations per minute per gram (d.p.m. g(-1)); n = 11) to 50 Hz (30 +/- 3 x 10(3) d.p.m. g(-1); n = 5). The P-type Ca(2+) channel blocker, omega-agatoxin IVA (100 nm) reduced (by 40 +/- 10%; n = 6) the release of [(3)H]ACh evoked by 50-Hz trains, while nifedipine (1 microM, an L-type blocker) was inactive. Tetanic depression was overcome (88 +/- 6 x 10(3) d.p.m. g(-1); n = 12) by stimulating the phrenic nerve with 50-Hz bursts (five bursts of 150 pulses, 20 s interburst interval). In these conditions, omega-agatoxin IVA (100 nM) failed to affect transmitter release, but nifedipine (1 microM) decreased [(3)H]ACh release by 21 +/- 7% (n = 4). Inactivation of endogenous adenosine with adenosine deaminase (ADA, 0.5 U ml(-1)) reduced (by 54 +/- 8%, n = 5) the release of [(3)H]ACh evoked with 50-Hz bursts. This effect was opposite to the excitatory actions of adenosine (0.5 mm), S-(p-nitrobenzyl)-6-thioinosine (5 microM, an adenosine uptake blocker) and CGS 21680C (3 nM, a selective A(2A) receptor agonist); as the A(1) receptor agonist R-N(6)-phenylisopropyl adenosine (R-PIA, 300 nM) failed to affect the release of [(3)H]ACh, the results indicate that adenosine generated during 50-Hz bursts exerts an A(2A)-receptor-mediated tonus. The effects of ADA (0.5 U ml(-1)) and CGS 21680C (3 nm) were prevented by nifedipine (1 microM). Blocking tonic A(2A) receptor activation, with ADA (0.5 U ml(-1)) or 3,7-dimethyl-1-propargyl xanthine (10 microM, an A(2A) antagonist), recovered omega-agatoxin IVA (100 nM) inhibition and caused the loss of function of nifedipine (1 microM). Data indicate that, in addition to the predominant P-type Ca(2+) current triggering ACh release during brief tetanic trains, motoneurones possess L-type channels that may be recruited to facilitate transmitter release during high-frequency bursts. The fine-tuning control of Ca(2+) influx through P- or L-type channels is likely to be mediated by endogenous adenosine. Therefore, tonic activation of presynaptic A(2A) receptors operating Ca(2+) influx via L-type channels may contribute to overcome tetanic depression during neuronal firing.
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Affiliation(s)
- Laura Oliveira
- Laboratório de Farmacologia, Instituto de Ciências Biomédicas de Abel Salazar, Universidade do Porto, L. Prof Abel Salazar 2, 4099-003 Porto, Portugal
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van Lunteren E, Moyer M, Kaminski HJ. Adverse effects of myasthenia gravis on rat phrenic diaphragm contractile performance. J Appl Physiol (1985) 2004; 97:895-901. [PMID: 15107414 DOI: 10.1152/japplphysiol.01266.2003] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Myasthenia gravis has variable effects on the respiratory system, ranging from no abnormalities to life-threatening respiratory failure. Studies characterized diaphragm muscle contractile performance in rat autoimmune myasthenia gravis. Rats received monoclonal antibody that recognizes acetylcholine receptor determinants (or inactive antibody); 3 days later, phrenic nerve and diaphragm were studied in vitro. Myasthenic rats segregated into two groups, those with normal vs. impaired limb muscle function when tested in intact animals ("mild" and "severe" myasthenic). Baseline diaphragm twitch force was reduced for both severe (P < 0.01) and mild (P < 0.05) myasthenic compared with control animals (twitch force: normal 1,352 +/- 140, mild myasthenic 672 +/- 99, severe myasthenic 687 +/- 74 g/cm2). However, only severe myasthenic diaphragm had impaired diaphragm endurance, based on significantly (P < 0.05) accelerated rate of peak force decline during the initial period of stimulation (0.02 + 0.02, 0.03 +/- 0.01, and 0.09 +/- 0.01%/pulse for normal, mild myasthenic, and severe myasthenic, respectively, during continuous stimulation) and intratrain fatigue (up to 30.5 +/- 7.4% intratrain force drop in severe myasthenic vs. none in normal and mild myasthenic, P < 0.01). Furthermore, compared with continuous stimulation, intermittent stimulation had a protective effect on force of severe myasthenic diaphragm (force after 2,000 pulses was 31.4 +/- 2.0% of initial during intermittent stimulation vs. 13.0 +/- 2.1% of initial during continuous stimulation, P < 0.01) but not on normal diaphragm. These data indicate that baseline force and fatigue may be affected to different extents by varying severity of myasthenia gravis and furthermore provide a mechanism by which alterations in breathing pattern may worsen respiratory muscle function in neuromuscular diseases.
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Affiliation(s)
- Erik van Lunteren
- Department of Medicine, (Pulmonary), Case Western Reserve University and Cleveland Department of Veterans Affairs Medical Center, Cleveland, Ohio 44106, USA.
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14
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van Lunteren E, Moyer M. Slowing of rat diaphragm action potential depolarization by endurance treadmill training. Neurosci Lett 2003; 339:175-8. [PMID: 12633881 DOI: 10.1016/s0304-3940(03)00031-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This study tested the hypothesis that the action potential properties of the diaphragm muscle are altered by endurance exercise treadmill training. Rats underwent treadmill running or sham training for 8 weeks, and intracellular electrophysiological recordings were subsequently performed in vitro. Diaphragm resting membrane potential was not altered by training. The maximal rate of action potential depolarization was reduced significantly by exercise training, from 551+/-16 to 445+/-15 mV/ms (P<0.00002). In contrast the rate of action potential repolarization was not significantly different between the two groups (P=0.25). Action potential height was significantly higher in control compared with trained muscle (84.5+/-1.0 vs. 78.4+/-1.2 mV, P<0.0005). The combination of slowed action depolarization and decreased peak action potential height resulted in no net change in action potential area. Thus treadmill running endurance exercise training slows rat diaphragm action potential depolarization but not repolarization, suggestive of altered Na+ but not K+ channel function.
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Affiliation(s)
- Erik van Lunteren
- Department of Medicine (Pulmonary) 111J(W), Case Western Reserve University and Cleveland VA Medical Center, 10701 East Boulevard, Cleveland, OH 44106, USA.
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Desaulniers P, Lavoie PA, Gardiner PF. Incomplete recovery of endplate potential amplitude while intermittently activating rat soleus neuromuscular junctions in situ. Muscle Nerve 2002; 26:810-6. [PMID: 12451606 DOI: 10.1002/mus.10275] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Studies dealing with neuromuscular transmission efficacy typically employ continuous patterns of activation to demonstrate decrements in endplate potential (epp) amplitude. Recent evidence from rat diaphragm muscle has shown that including periods of quiescence to the stimulation protocol allows epp amplitude to recover between series of contractions. Whether similar recovery occurs in rat hindlimb muscle is unknown. In this study, we have measured declines in epp amplitude in rat soleus muscle during trains of stimulation evoked either continuously (10 s) or intermittently (400 ms repeated every second), using an in situ approach. As in diaphragm, we found that rest periods within the intermittent trains significantly improved neuromuscular transmission efficacy. However, unlike the diaphragm, epp amplitude recovery was incomplete even by the second train in the intermittent protocols, recovery being frequency-dependent and ranging from 40 to 50%. The results suggest that the kinetics of epp amplitude rundown and recovery may be muscle-specific, and should be considered when evaluating situations in which neuromuscular transmission efficacy may be altered.
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Affiliation(s)
- Patrice Desaulniers
- Département de Kinésiologie, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec H3C-3J7, Canada
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16
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Moyer M, van Lunteren E. Effect of Temperature on Endplate Potential Rundown and Recovery in Rat Diaphragm. J Neurophysiol 2001; 85:2070-5. [PMID: 11353023 DOI: 10.1152/jn.2001.85.5.2070] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The amplitude of neuromuscular junction end-plate potentials (EPPs) decreases quickly within a train but recovers nearly completely from train to train during intermittent stimulation. Rundown has been shown to be dependent not only on the rate of transmitter release but also on the rate of replenishment of the depleted neurotransmitter at the site of release. Two groups of processes have been proposed for synaptic vesicle recycling, both of which involve multiple energy-requiring steps and enzymatic reactions and which therefore would be expected to be very temperature-sensitive. The present study tested the hypothesis that low temperature therefore increases the rate of EPP amplitude rundown. Studies were performed in vitro on rat diaphragm and used μ-conotoxin to allow normal-sized EPPs to be recorded from intact fibers. EPP amplitude rundown during intermittent stimulation at 20 and 50 Hz (duty cycle 333 ms) was greater at 20°C than it was at 37°C. Initially, temperature affected only intra-train rundown but, over longer periods of stimulation, both intra- and inter-train rundown were significantly accelerated by cold temperature. Cumulative EPP amplitudes were calculated by successively adding the amplitudes of each EPP during the stimulation period to provide an estimate of total neurotransmitter release in the neuromuscular junction. The cumulative EPP amplitude was significantly lower at 20°C than it was at 37°C during both 20 and 50 Hz stimulation. These data indicate that the mechanism involved in EPP amplitude rundown and recovery is temperature-sensitive, with a greater decrement in EPP amplitude at cold than at warm temperatures.
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Affiliation(s)
- M Moyer
- Pulmonary Division, Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA
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