RESUMO
The experiments of modeling hypogravity using fluorescent microscopy have shown a decrease of expression of b1 of Na +/K+-ATPase and Ca2+-ATPase subunits and the increase in the insensitivity of synthesis of a1S subunit of the L-type Ca2+-channel of the plasmatic membrane, whereas the synthesis of a2 subunit of Na+/K+-ATPase does not change. In «fast¼ muscle only observed similar for «slow¼ muscle decrease in the expression of b1 subunit without changing other parameters were studied. However, the decrease in fluorescence b1 subunit due to spread of data was not statistically significant. Thus hypogravity adversely affects the functioning primarily skeletal muscles, providing static load.
Assuntos
Canais de Cálcio Tipo L/biossíntese , Hipergravidade , Fibras Musculares de Contração Lenta/metabolismo , ATPases Transportadoras de Cálcio do Retículo Sarcoplasmático/biossíntese , ATPase Trocadora de Sódio-Potássio/biossíntese , Animais , Masculino , Microscopia de Fluorescência , Fibras Musculares de Contração Lenta/patologia , Ratos , Ratos WistarRESUMO
Experiments on neuromuscular synapses of rats at different stages of ontogenesis have been performed. It has been found that one of the reasons of higher asynchrony of the release of single quanta of acetylcholine in the synapses of newborn animals is the activity of the presynaptic dihydropyridine-sensitive calcium channels of the L-type.
Assuntos
Acetilcolina/metabolismo , Canais de Cálcio Tipo L/fisiologia , Ativação do Canal Iônico/fisiologia , Junção Neuromuscular/fisiologia , Neurotransmissores/metabolismo , Transmissão Sináptica/fisiologia , Animais , Animais Recém-Nascidos , Bloqueadores dos Canais de Cálcio/administração & dosagem , Canais de Cálcio Tipo L/efeitos dos fármacos , Di-Hidropiridinas/administração & dosagem , Relação Dose-Resposta a Droga , Técnicas In Vitro , Ativação do Canal Iônico/efeitos dos fármacos , Neurogênese/fisiologia , Junção Neuromuscular/efeitos dos fármacos , Ratos , Ratos Wistar , Transmissão Sináptica/efeitos dos fármacosRESUMO
in the synapses of the "fast" (m. EDL) and "slow" (m. soleus) skeletal muscles of the rat GABABR1 and GABABR2 subunits of metabotropic receptors for γ-aminobutyric acid (GABA), located primarily on the motor nerve ending membrane were detected by immunohistochemistry and fluorescence microscopy methods.
Assuntos
Junção Neuromuscular/metabolismo , Receptores de GABA-B/metabolismo , Animais , Imuno-Histoquímica , Transporte Proteico , RatosRESUMO
Antiorthostatic hindlimb suspension reduces resting membrane potential of rat fast and slow muscles within 7 days. Changes in Na+/K+ pump activity and shifts of the equilibrium potential for chloride ions are the main mechanism of the changes in the resting potential of muscle fibers. The latter is presumably associated with increased intracellular ion current due to activation of the second active Na+, K+, 2Cl- symport. Reduction of the membrane potential is related to muscle denervation. However, membrane depolarization of muscle fibers during antiorthostatic suspension cannot be explained solely by changes in the mechanisms of neurotrophic control from motor neurons.
Assuntos
Cloretos/metabolismo , Hipogravidade , Potenciais da Membrana , Modelos Biológicos , Músculo Esquelético/fisiologia , Animais , Masculino , Ratos , Ratos WistarRESUMO
Using immunofluorescent techniques, we have revealed that, after 35 days of rats hindlimb unloading, neuromuscular synapses of fast and slow muscles show enhanced fluorescence intensity and decreased area of fluorescent staining of acetylcholine receptors; increased fluorescent intensity and area of fluorescent staining for acetylcholinesterase. The ratio of the number of postsynaptic acetylcholine receptors and the amount of acetylcholinesterase changed as well as their spatial position in relation to each other. These rearrangements correspond to electrophysiological data on the reduction of the amplitude of the miniature endplate currents in both muscles. Identified synapses restructuring accompanied by a decrease in the volume of muscle fibers. Hindlimb unloading (simulation of hypogravity) leads to an increase in functional activity of acetylcholinesterase on the background of reduced postsynaptic membrane area occupied by acetylcholine receptors. This leads to a decrease in the amplitude of excitatory postsynaptic potentials thereby reducing the nerve-muscle excitation transmission safety factor.
Assuntos
Acetilcolinesterase/metabolismo , Elevação dos Membros Posteriores , Fibras Musculares de Contração Rápida/metabolismo , Fibras Musculares de Contração Lenta/metabolismo , Junção Neuromuscular/ultraestrutura , Receptores Colinérgicos/ultraestrutura , Acetilcolina/metabolismo , Animais , Potenciais Pós-Sinápticos Excitadores/fisiologia , Humanos , Masculino , Potenciais Pós-Sinápticos em Miniatura/fisiologia , Fibras Musculares de Contração Rápida/ultraestrutura , Fibras Musculares de Contração Lenta/ultraestrutura , Junção Neuromuscular/metabolismo , Ratos , Ratos Wistar , Receptores Colinérgicos/metabolismo , Sinapses/metabolismo , Sinapses/ultraestrutura , Transmissão SinápticaRESUMO
When modeling effects of hypogravitation by the method of hindlimb unloading in rats the area of cross-section in lumbar part of a spinal cord was found to reduce. The analysis of spinal cord slides showed that these changes are associated with a decrease in the area of white substance of a spinal cord. Data obtained are consistent with our previous observation of a decrease in expression of the genes encoding myelin proteins. Results of our researches give the good reasons to believe that miyelinization failure in CNS is one of the factors that underlie the development of hypogravitational motor syndrome.
Assuntos
Leucoencefalopatias/patologia , Transtornos das Habilidades Motoras/patologia , Bainha de Mielina/patologia , Medula Espinal/patologia , Animais , Elevação dos Membros Posteriores , Histocitoquímica , Hipogravidade/efeitos adversos , Leucoencefalopatias/etiologia , Região Lombossacral , Masculino , Transtornos das Habilidades Motoras/etiologia , Ratos , Ratos Wistar , Síndrome , Simulação de Ausência de PesoRESUMO
The miniature excitatory postsynaptic currents (MEPCs) of the muscle cells of the earthworm Lumbricus terrestris were recorded by glass microelectrodes. In a single synaptic zone, three types of MEPC were recorded: a fast single-exponential type that decayed with tau =0.9 ms, a slow single-exponential with tau = 9.2 ms and a two-exponential MEPC with tau = 1.3 and 8.5 ms, respectively. The muscle cells of earthworms contain populations of yet-unidentified ionic channels that might be different from the common nicotinic and muscarinic groups of acetylcholine receptors, since these MEPCs are not sensitive to d-tubocurarine, atropine, benzohexonium or proserine. Alternatively, besides ACh receptors, the membrane may contain receptors for another yet-unidentified excitatory transmitter.
Assuntos
Canais Iônicos/metabolismo , Músculos/inervação , Junção Neuromuscular/metabolismo , Oligoquetos/metabolismo , Transmissão Sináptica , Animais , Antagonistas Colinérgicos/farmacologia , Potenciais Pós-Sinápticos Excitadores , Técnicas In Vitro , Canais Iônicos/efeitos dos fármacos , Junção Neuromuscular/efeitos dos fármacos , Transmissão Sináptica/efeitos dos fármacos , Fatores de TempoRESUMO
The effect of Na+-K+-ATPase inhibitor ouabain on the resting membrane potential (Vm) was studied by glass microelectrodes in isolated somatic longitudinal muscles of the earthworm Lumbricus terrestris and compared with frog sartorius muscle. In earthworm muscle, Vm was -49 mV (inside negative) in a reference external solution with 4 mmol/l K+. The electrogenic participation of Na+-K+-ATPase was absent in solutions with very low concentrations of 0.01 mmol/l K+, higher in 4 and 8 mmol/l K+ (4-5 mV) and maximal (13 mV) in solutions containing 12 mmol/l K+ where Vm was -46 mV in the absence and -33 mV in the presence of 1 x 10(4) M ouabain. The electrogenic participation of Na+-K+-ATPase was much smaller in m. sartorius of the frog Rana temporaria bathed in 8 and 12 mmol/l K+. The results indicate that the Na+-K+-ATPase is an important electrogenic factor in earthworm longitudinal muscle fibres and that its contribution to Vm depends directly on the concentration of K+ in the bathing solution.
Assuntos
Potenciais da Membrana/fisiologia , Músculos/fisiologia , ATPase Trocadora de Sódio-Potássio/fisiologia , Animais , OligoquetosRESUMO
The resting membrane potential (V(m)) of isolated somatic longitudinal muscles of the earthworm Lumbricus terrestris was studied by glass microelectrodes. The inhibition of chloride permeability by low pH did not affect V(m) of the muscle fibers in isolated somatic longitudinal muscles of the earthworm Lumbricus terrestris which was -48.7 mV (inside negative) at pH 7.3 and -49.1 at pH 5.6. On the other hand, bathing the muscles in Cl(-) and Na(+)-free solutions, or application of the chloride transporter inhibitor furosemide and Na(+)-K(+)-ATPase inhibitor ouabain depolarized the V(m) by 3-5 mV. The effects of a Cl(-) -free solution and ouabain were not additive. This demonstrates relatively small contribution of equilibrium potential for Cl(-) to the resting membrane potential and electrogenic effect of Na(+)K(+)-ATPase which is dependent on the supply of Na(+)(i) ions by furosemide-sensitive and Cl(-)(e)- and Na(+)(e)-dependent electroneutral transport (most probably Na(+)K(+)Cl(-) cotransport).
Assuntos
Cloretos/metabolismo , Transporte de Íons/fisiologia , Músculos/fisiologia , Oligoquetos/fisiologia , Animais , Cloretos/farmacologia , Eletrofisiologia , Furosemida/farmacologia , Concentração de Íons de Hidrogênio , Técnicas In Vitro , Potenciais da Membrana/efeitos dos fármacos , Potenciais da Membrana/fisiologia , Fibras Musculares Esqueléticas/efeitos dos fármacos , Fibras Musculares Esqueléticas/fisiologia , Concentração Osmolar , Ouabaína/farmacologia , Potássio/farmacologia , Sódio/farmacologia , Inibidores de Simportadores de Cloreto de Sódio e Potássio , Simportadores de Cloreto de Sódio-Potássio/fisiologia , ATPase Trocadora de Sódio-Potássio/antagonistas & inibidoresRESUMO
On the nerve-muscle preparation of rats diaphragm muscle on different stages of postnatal development, the comparison of morphological features and functions of synaptic apparatus, including induced secretion time parameters was carried out. It was found that, along with the reduced, compared to the adult animals, area of nerve endings in the newborn the speed of the motor nerve excitation was slower, intensity of spontaneous and induced secretion of quantum fluctuations was reduced and real synaptic delays in the end plate were intense. Severe degree of acetylcholine quanta asynchronous secretion with longer open state of the ion channel in newborns synapses can compensate reduction in reliability of synaptic transmission due to a decrease of the quantal content of the postsynaptic response.
Assuntos
Acetilcolina/metabolismo , Diafragma/crescimento & desenvolvimento , Placa Motora/fisiologia , Neurônios Motores/fisiologia , Sinapses/fisiologia , Fatores Etários , Animais , Animais Recém-Nascidos , Potenciais Pós-Sinápticos Excitadores , Microeletrodos , Ratos , Reprodutibilidade dos Testes , Transmissão Sináptica/fisiologia , Técnicas de Cultura de TecidosRESUMO
It is well known that antagonists of N-type voltage-gated calcium channels inhibit the evoked quantal release of acetylcholine in amphibian neuromuscular synapses. This, however, does not exclude the functional expression of other types of voltage-gated calcium channels in these nerve terminals. Using immunocytochemistry, we detected the expression of the alpha1A subunit of P/Q-type calcium channels (that is otherwise typical of mammalian motor nerve endings) in the frog neuromuscular junction. In addition, we demonstrated that the P/Q-type channel blocker omega-agatoxin IVA (20 nM) reduced the action potential-induced calcium transient and significantly decreased both spontaneous and evoked mediator release. Our data indicates the functional expression of P/Q-type calcium channels in the frog motor nerve ending which participate in acetylcholine release.
Assuntos
Sinalização do Cálcio/fisiologia , Cálcio/metabolismo , Ativação do Canal Iônico/fisiologia , Potenciais da Membrana/fisiologia , Junção Neuromuscular/fisiologia , Transmissão Sináptica/fisiologia , Animais , Rana ridibundaAssuntos
Acetilcolina/metabolismo , Canais de Cálcio Tipo T/metabolismo , Junção Neuromuscular/metabolismo , Animais , Bloqueadores dos Canais de Cálcio/farmacologia , Canais de Cálcio Tipo T/imunologia , Técnicas In Vitro , Mibefradil/farmacologia , Junção Neuromuscular/efeitos dos fármacos , Rana ridibundaAssuntos
Acetilcolina/metabolismo , Hipogravidade/efeitos adversos , Neurônios Motores/metabolismo , Junção Neuromuscular/metabolismo , Animais , Masculino , Potenciais da Membrana , Fibras Musculares Esqueléticas/metabolismo , Junção Neuromuscular/fisiopatologia , Ratos , Ratos Wistar , Voo Espacial , SíndromeRESUMO
Potential created by electrogenic ionic pumps under conditions of maximum activation in a warm standard ionic medium with K(+) after preincubation in cold potassium-free solution has two components: a higher ouabaine-insensitive "stationary" component, and a lower "regulatory" component sensitive to ouabaine, furosemide, and removal of Cl(-) or Ca(2+) from the medium. Functional heterogeneity of electrogenic ionic pumps is hypothesized implying the existence of two components: "stationary" (not regulated extracellularly) and "regulatory" (controlled and directly related to active Cl(-) transfer).
Assuntos
Células Musculares/efeitos dos fármacos , Células Musculares/metabolismo , Oligoquetos/fisiologia , Sarcolema/efeitos dos fármacos , Animais , Cálcio/metabolismo , Cloretos/metabolismo , Meios de Cultura , Relação Dose-Resposta a Droga , Inibidores Enzimáticos/farmacologia , Furosemida/farmacologia , Agonistas GABAérgicos/classificação , Agonistas GABAérgicos/farmacologia , Íons/farmacologia , Potenciais da Membrana/efeitos dos fármacos , Oligoquetos/metabolismo , Ouabaína/farmacologia , Potássio/metabolismo , Potássio/farmacologia , Sarcolema/metabolismo , Sódio/metabolismo , Sódio/farmacologia , Inibidores de Simportadores de Cloreto de Sódio e Potássio/farmacologia , ATPase Trocadora de Sódio-Potássio/fisiologiaRESUMO
GABA, baclofen, epinephrine, and norepinephrine hyperpolarized the membrane of earthworm somatic cells. This effect was prevented by furosemide, removal of Cl- from the medium, or activation of Na+/K+ pump by 3-fold increase external potassium concentration. It was hypothesized that GABA, baclofen, epinephrine, and norepinephrine stimulate Na+/K+ transport via specific receptor inputs, but their effect on resting potential can be realized only under conditions of working Cl- symport.
Assuntos
Adrenérgicos/farmacologia , GABAérgicos/farmacologia , Potenciais da Membrana/efeitos dos fármacos , Músculos/efeitos dos fármacos , Oligoquetos/metabolismo , Simportadores de Cloreto de Sódio/metabolismo , ATPase Trocadora de Sódio-Potássio/metabolismo , Animais , Músculos/metabolismoRESUMO
Miniature stimulating postsynaptic currents of Lumbricus terrestris somatic muscle cells were recorded. Atropine, d-tubocurarin, alpha-bungarotoxin, carbacholine, and proserin did not modify the amplitude and temporal parameters of miniature stimulatory postsynaptic currents, while carbacholine and nicotine depolarized the muscle membrane. Presumably, Lumbricus terrestris muscle cells contain acetylcholine-sensitive channel-receptor complexes not belonging to classical nicotinic or muscarinic acetylcholine receptors.
Assuntos
Agonistas Colinérgicos/farmacologia , Antagonistas Colinérgicos/farmacologia , Potenciais Pós-Sinápticos Excitadores/fisiologia , Canais Iônicos/fisiologia , Células Musculares/fisiologia , Oligoquetos/fisiologia , Animais , Atropina/farmacologia , Bungarotoxinas/farmacologia , Carbacol/farmacologia , Neostigmina/farmacologia , Nicotina/farmacologia , Oligoquetos/citologia , Receptores Colinérgicos/efeitos dos fármacos , Tubocurarina/farmacologiaRESUMO
Carbacholine depolarizes Lumbricus terrestris myocyte membrane. Addition of verapamil, tetrodotoxin, removal of K(+), Cl(-), and Ca(2+), and replacement of Ca(2+)with Mn(2+)in the bathing solution did not prevent the carbacholine-induced decrease in resting potential, but in a sodium-free medium carbacholine was ineffective. It was hypothesized that depolarization of the sarcolemma resulting from activation of cholinomimetic-sensitive channel-receptor complex of the Lumbricus terrestris somatic muscle cells is primarily determined by sodium permeability of the membrane.
Assuntos
Carbacol/farmacologia , Células Musculares/efeitos dos fármacos , Células Musculares/metabolismo , Animais , Meios de Cultura , Técnicas In Vitro , Íons/farmacologia , Potenciais da Membrana/efeitos dos fármacos , Oligoquetos , Sarcolema/efeitos dos fármacos , Sarcolema/metabolismo , Sódio/metabolismo , Sódio/farmacologia , Tetrodotoxina/farmacologia , Verapamil/farmacologiaRESUMO
Three types of miniature excitatory synaptic currents were recorded in the same synaptic region of earthworm muscle cells: monoexponential (tau=1.2 msec) and biexponential (tau(1)=1.2 and tau(2)=8.0 msec). It was hypothesized that earthworm muscle cells contain at least two populations of acetylcholine-sensitive ionic channels, which do not belong to classical nicotinic and muscarinic acetylcholine receptors.
Assuntos
Potenciais Pós-Sinápticos Excitadores/fisiologia , Canais Iônicos/fisiologia , Células Musculares/fisiologia , Oligoquetos/fisiologia , Animais , Espaço Extracelular/fisiologia , Cinética , Junção Neuromuscular/fisiologia , Oligoquetos/citologia , Sinapses/fisiologiaRESUMO
Carbachol in a concentration of 5x10(-8) mol/liter does not hyperpolarize, and in a concentration of 5x10(-6) mol/liter depolarizes the membrane of somatic muscle cell in earthworm. d-tubocurarine, alpha-bungarotoxin, atropine, and hexamethonium added to the incubation medium did not abolish the carbachol-induced decrease in resting membrane potential. Each of these drugs alone had no effect on resting membrane potential in muscle cells. Presumably, the acetylcholine-sensitive receptor-channel membrane complex in earthworm muscle cell differs from acetylcholine receptor in skeletal muscle fibers and peripheral neurons of vertebrates.
Assuntos
Carbacol/farmacologia , Agonistas Colinérgicos/farmacologia , Potenciais da Membrana/efeitos dos fármacos , Músculos/citologia , Acetilcolina/farmacologia , Animais , Atropina/farmacologia , Bungarotoxinas/farmacologia , Bloqueadores Ganglionares/farmacologia , Hexametônio/farmacologia , Antagonistas Muscarínicos/farmacologia , Antagonistas Nicotínicos/farmacologia , Oligoquetos , Tubocurarina/farmacologiaRESUMO
Serotonin, glutamate, glycine, ATP, and muscarine had no effect on resting membrane potential of muscle cell in earthworm Lumbricus terrestris. Nicotine depolarizes and GABA hyperpolarizes the muscle membrane. Removal of K(+), Cl(-) and addition of ouabaine and strychnine to the solution abolished the effect of GABA. The authors conclude that the Lumbricus terrestris myocyte membrane contains nicotine receptors and GABAergic receptors sensitive to strychnine. Stimulation of these receptors activates sarcolemmal ionic pumps and causes membrane hyperpolarization.