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At least 1,243 records · Page 69Linked to original sources
PubMed1978

Competitive antagonism between calcium and antibiotics at the neuromuscular junction.

The neuromuscular blockade produced by the amino-glycosidic-aminocyclitolic antibiotics streptomycin and kanamycin and its reversal by calcium was quantitatively studied in the isolated phrenic nerve-diaphragm preparation of the rat. The low dose-response curves obtained presenting no significant deviation from parallelism are highly suggestive of a competitive type of antagonism between those substances. The streptidinic moiety of streptomycin showed the same properties as the original antibiotic. Streptomycin and kanamycin decreased the amplitude of intracellularly recorded e.p.p.'s of the toad sartorius muscle in a manner quite similar to that described for magnesium ions which suggests an interference of the antibiotics with the cooperative interaction of calcium ions with specific receptive sites at the presynaptic membrane of the neuromuscular junction.

Animals↗
PubMed1983

Cooperative interaction among cell surface sites: evidence in support of the surface adsorption theory of cellular electrical potentials.

Resting potentials were studied in frog sartorius muscles equilibrated in Ringer solutions that contained various concentrations of K+. Cells in solutions that contained near-zero K+ showed a rise in potential followed by a slow decline over about 70 hours that paralleled the loss of cellular K+ in exchange for Na+. When these cells were placed in 2.5 mM K+, the re-gain of the potential occurred much more rapidly than the re-gain of cellular K+. Thus, there was no consistent relation between resting potential and concentration of intracellular K+. When cells were immersed in solutions containing 100 mM Na+ and K+ at concentrations of 2.5 mM and greater, there was a semi-logarithmic relation between potential and [K+]ex, in which potential declined as [K+]ex increased. However, when cells were equilibrated in [K+]ex below 2.5 mM, the potential peaked and then declined as [K+]ex decreased. The results are readily explained by the surface adsorption model of the cellular potential, in which the potential is determined simply by the nature of the fixed surface charges that interact with one another in a cooperative manner. The peak and decline of the potential with decreasing [K+]ex below 2.5 mM mirrors the autocooperative shift in the affinity of the surface charged sites from one that favors K+ over Na+ strongly to one that favors K+ over Na+ less strongly.

Animals↗
PubMed1982

[Determination of dissociation exponent of CO2 used in Henderson-Hasselbalch equation by means of bicarbonate-selective microelectrode].

To measure intracellular ion activity of bicarbonate directly, a double-barreled bicarbonate-selective microelectrode was constructed with a liquid ion exchanger(LIX) containing tri-n-octylammonium, trifluoroacetyl-butyl benzene and octanol. A new dissociation exponent of CO2 (pK') was determined experimentally for a modified Henderson-Hasselbalch equation, in which HCO3 activity was used instead of HCO3 concentration. The temperature effects on pK' and solubility coefficient of CO2 were analyzed over the range of 10 to 40 degrees C. The average values of pK' at room temperature (22 degrees C) were 6.377 and 6.348 in water and frog serum, respectively, and the solubility coefficients of CO2 were 0.048 and 0.046 mM/L/mmHg. The values of pK' plotted on Arrhenius plot were shown linear with 1/T, indicating that the pK' thus obtained can be treated thermodynamically as a first-order kinetics. Under normal circumstances, the values for the intracellular pH predicted from the intracellular bicarbonate activities in the proximal tubule and sartorius muscle of bullfrogs were virtually identical with those obtained directly by the LIX-pH-microelectrodes.

Animals↗
PubMed1983

Interaction of cholinergic ligands with the purified acetylcholine receptor protein. I. Equilibrium binding studies.

We have studied the binding equilibria of two fluorescent ligands and several nonfluorescent cholinergic ligands with the purified acetylcholine receptor from Electrophorus electricus. The assay was based on the specifically cholinergic and reversible quenching of fluorescence observed upon complex formation between the receptor protein and N-7-(4-nitrobenzo-2-oxa-1,3-diazole)-5-aminopentanoic acid beta-(N-trimethylammonium) ethyl ester. This way, a large body of accurate, true equilibrium data was obtained. We find 1) all ligands studied compete for the same number of binding sites at the receptor; 2) agonists compete for half of these sites with high affinity and for the other half of these sites with significantly lower affinity; 3) antagonists compete for all of these sites with one affinity; and 4) in the presence of disulfide reducing agents, the binding patterns of some agonists and antagonists are changed in accordance with the electrophysiological changes observed under the same conditions with Rana pipiens Sartorius muscle fibers. Our studies indicate that the mechanism of ligand recognition is still functional at equilibrium and is not subject to the presence of an intact membrane environment. Furthermore, the existence of two types of agonist sites at every receptor molecule excludes most of the presently discussed two-state models as the basis for a mechanism of receptor-ligand interaction. To explain sigmoidal dose-response curves, a two-site model is already sufficient.

4-Chloro-7-nitrobenzofurazan↗
PubMed1980

Sodium dependence of membrane potential oscillation induced by veratrine.

The dependence of the membrane potential oscillation on extracellular sodium concentration was studied in the frog sartorius muscle. (1) When Na concentration of the Ringer solution was decreased to zero, the membrane potential oscillation cesed and the membrane tended to repolarize. This inhibitory effect was reversible. (2) Tetrodotoxin, 10(-7) g/ml, inhibited the development of membrane potential oscillation or stopped within 2--4 min the membrane potential oscillation already developed, the membrane then became partly repolarized maximum to -72mV. The inhibitory effect of tetrodotoxin was also reversible. (3) When the Na concentration of the Ringer solution was reduced to 60 mM the latency time of the membrane potential oscillation did not change. By further decreasing the Na concentration the latency time increased in a hyperbolic function. In case of 10 mM Na the latency period was 7 times longer than the control. (4) The depolarizing effect of veratrine was linearly related to the logarithm of Na concentration in a range from 10 to 120 mM Na. (5). By decreasing the [Na]c from 120 to 10 mM the frequency of oscillation decreased and the amplitude increased linearly as a function of the logarithm of Na concentration.

Animals↗
PubMed1982

[Statistical analysis of calcium accumulation in nerve endings during rhythmic stimulation].

The extracellular recording was used to examine the evoked transmitter release in neuromuscular junctions of the frog sartorius muscle at pair and repetitive stimulations. The repetitive stimulation with low initial level of secretion (the quantum content 0.1-0.5) led to the increased transmitter release. Statistical analysis showed that the probability of the quantum transmitter release in response to each stimulus was increased. The method of conditioned probabilities revealed a decrease in the probability of the quantum release provided the previous stimulus had induced the secretion of the acetylcholine quantum. It is assumed that at the moment of the quantum transmitter release (or promptly after it) a certain quantity of Ca2+ leaves the nerve terminal cytoplasm, thereby significantly reducing the intracellular concentration of calcium.

Animals↗
PubMed1982

[Model of mediator secretion at a neuromuscular synapse based on the spatial heterogeneity of the probability of acetylcholine quantum release].

A spatial heterogeneity of the probability of the mediator quantum release (pt) along the nerve terminal was found in experiments on frog sartorius muscle with extracellular recording of end-plate potentials. The expression of Ca2+ ions effect depended upon the initial pt. With intracellular recording the increase of Ca2+ concentration from 0.2 to 1.8 mM was accompanied by increase of n and p binomial parameters. On the basis of the obtained data a model of mediator release at neuromuscular synapsis is proposed, which allows the estimation of the coefficients of pt distribution along the nerve terminal and the number of acting release sites. For estimation of these parameters it is necessary to calculate the n and p at two different Ca2+ ion concentrations.

Acetylcholine↗
PubMed1981

[Microcalorimetric and myographic analysis of the causes of changes in the ratio of heat loss to work accomplished during muscular activity].

In the frog non-fatigued sartorius muscle, raise of the ratio of muscle-emanated heat to the performed mechanical work is due to the aerobic delayed heat production. The heat emanation reflects the respiratory resynthesis of macroergs used for subsequent contractile muscle activity. Contrary to that, raise of the ratio in fatigued muscle reflects the excitation-contraction coupling disturbance and a specific increase of the energy supply for excitable link.

Adenosine Triphosphate↗
PubMed1981

[Is the presynaptic action of carbocholine related to the activation of the postsynaptic membrane?].

Experiments were carried out to elucidate whether carbacholine (CCh) exerts a direct effect on motor nerve endings. With this purpose in view the frog sartorius muscle was used to correlate changes in the quantum content of end plate potentials (EPP) with the carbacholine-induced depolarization of the postsynaptic membrane. It was disclosed in the first series of experiments on neuromuscular preparations blocked by the decreased Ca2+ concentration in Ringer solution that CCh lowers EPP at a concentration which produces no depolarizing action on the postsynaptic membrane (5 x 10(-7) mol/l). In the second series of experiments on preparations blocked by transversal dissection of muscle fibers, CCh (5 x 10-6) mol/l) also diminished EEP without affecting the membrane potential of the muscle fibers. In the third series of experiments, the presynaptic effect of the third series of experiments, the presynaptic effect of CCh (5 x 10(-6) mol/l) was reversed by tubocurarine (1 X 10(-7) mol/l), with the postsynaptic action of the mimetic remaining unchanged. The data obtained indicate that the decrease in EPP induced by CCh (5 x 10(-7)--5 x 10(-6) mol/l) does not arise from the depolarization of the end plate.

Animals↗
PubMedDate not supplied

Voluminous solitary non-Hodgkin extraganglionary lymphoma of thigh.

The case of a 36-year-old woman is presented. She had a voluminous tumour inside the 1/3 average part of the right thigh at 12 cm from the inguinal region. Apart from some local pains, she had a normal haematological formula, normal spleen, liver and lymph nodes. As the tumour of 5.5 x 5 x 4.5 cm was well incapsulated between the sartorius muscle and the great adductor tendon it was easily extirpated and presented a whitish-light yellow section. The histological cellular aspect was pleiomorphic with round, ovalar cells; some were big and clear cells of centroblast-type with several mitoses and giant multinucleated cells and collagenic bundles in between. The nodular Hodgkin sclerosis is not confirmed immunohistochemically because of the negative reaction for antigen Kil (CD30) so that the diagnosis was lymphoma with lymphoma with big B cells by CD20 reaction. We also found positive T cells at CD43 that might be reactive lymphocytes. The tumour ranks a rare malignant lymphoma and for the first time, an extraganglionar lymphoma in thigh was found. We have not met such a location in the literature.

Adult↗
PubMed1994

Extension of synaptic extracellular matrix during nerve terminal sprouting in living frog neuromuscular junctions.

Remodeling of the synaptic extracellular matrix (ECM) and its dynamic relationship with nerve terminal plasticity have been demonstrated in normal frog neuromuscular junctions (NMJs) in vivo (Chen et al., 1991). Our previous work has led to a hypothesis that extension of synaptic ECM precedes nerve terminal growth during synaptic remodeling. To test this hypothesis, the present study examined the changes of synaptic ECM in frog NMJs that were primarily undergoing nerve terminal growth and sprouting. Frog sartorius muscles were double stained with a fluorescent nerve terminal dye (4-Di-2-Asp) and rhodamine-tagged peanut agglutinin (PNA), which recognizes synaptic ECM. The double-labeled NMJs were visualized in vivo with video-enhanced fluorescence microscopy. Nerve sprouting was then induced in the muscle by grafting segments of the contralateral sciatic nerve. The identified NMJs were restrained and reexamined 2-3 months later. Extensive sprouting was observed in 46% of 167 identified NMJs. At junctional regions that showed extension or formation of new branches, synaptic ECM was commonly seen to have the same shape and distribution as the nerve terminal. However, extension of synaptic ECM beyond the corresponding nerve terminals, often by tens of microns, was observed in 29% of these newly formed junctional regions. This lack of correlation might be transient, as growth of nerve terminals following extended, PNA-stained ECM was seen. Examination with histological staining not only confirmed a lack of nerve terminal at the extended synaptic ECM region but also indicated an absence of AChE and postsynaptic junctional folds. The absence of these postsynaptic specializations at the extended, PNA-stained ECM region makes it unlikely that this region was previously occupied by nerve terminals that had retracted. Thus, the present study provides further findings consistent with the hypothesis that synaptic ECM precedes nerve terminal outgrowth and that the extension of synaptic ECM may play a role in synaptic remodeling.

Animals↗
PubMed1993

The preferential use of the external iliac artery as an inflow source for redo femoropopliteal and infrapopliteal bypass.

PURPOSE: It is believed that secondary operations involving the inguinal region are associated with a significant morbidity that includes infection, lymphatic obstruction, lymphorrhea, and neurovascular injury. To prevent these potentially important complications we have avoided a redo groin incision in 38 patients with severely symptomatic disease who had primary (23 cases) or secondary (15 cases) femoropopliteal bypass thrombosis during the past 3 years. METHODS: All patients were candidates for prosthetic bypasses because of lack of a suitable vein. Twenty-nine external iliac-to-popliteal bypasses (18 above-knee; 11 below-knee) and nine external iliac-to-infrapopliteal bypasses (five anterior tibial; two posterior tibial; two peroneal) were performed with 6 mm polytetrafluoroethylene ringed grafts in 38 patients. Adjunctive distal arteriovenous fistulas were constructed in all infrapopliteal bypasses. The external iliac artery was exposed via a retroperitoneal approach. The second incision was placed just below the scarred area and deepened to the level of the medial border of the sartorius muscle. A tunnel that connected both incisions was easily created by blunt dissection alongside the anterolateral border of the femoral artery. RESULTS: Four popliteal bypasses occluded at 4, 6, 10, and 28 months after operation. The remaining 25 grafts are patent (mean 14 months). Three of the infrapopliteal bypasses occluded at 0, 2, and 3 months after operation. The remaining six grafts are patent with follow-up from 4 to 18 months (mean 12 months). Only one patient had a superficial wound infection at the below-knee popliteal incision, which healed with local treatment. All other patients had an uneventful postoperative course. CONCLUSIONS: Thus we believe this approach to be simple, safe, and durable and should be used preferentially to avoid the difficult and hazardous dissection of a previously operated groin.

Aged↗
PubMed1977

Pregnancy diagnosis in the guinea pig.

A method for diagnosing pregnancy in the guinea pig by manual palpation was developed. Using this technique, pregnancy was detected between the 15th and 30th day of gestation with 98% accuracy. The 2% error consisted of animals that were pregnant but diagnosed as nonpregnant. Common mistakes that led to diagnosing nonpregnant animals as pregnant were: (1) palpation of fecal pellets; (2) palpation of left kidney; and (3) palpation of the sartorius muscle. Common errors that led to diagnosing pregnant animals as nonpregnant were: (1) failure to search the entire abdomen; (2) too close apposition of thumb and forefingers while searching the abdomen; and (3) failure to deprive animals of feed before palpation.

Animals↗
PubMed1995

[A potentially new sodium channel blocker: 2-chloro-4-bromo-alpha-methylcinnamic acid].

The effects of 2-Chloro-4-Bromo-alpha-Methylcinnamic acid sodium (SC1001 Na) and some channel antagonists on the action potential (AP) and the resting potential (RP) were tested intracellularly in the sartorius muscle of the toad (Bufo bufo gargarizans). TEA (10mmol/L) and MnCl2 (10 mmol/L) had no effect on the amplitude of the AP, otherwise, TTX (1 mumol/L) blocked the AP completely. SC1001 Na at the concentration of 2mmol/L largely decreased the amplitude of the AP and expanded the duration of the AP (measured at 1/2 peak amplitude), but it had no effect on the RP. The effects of ms group of drug were reversible. Under the pretreatment of the muscle preparation with TEA (10 mmol/L), SC1001 Na still increased the duration of the AP while decreased its amplitude. At the concentration of 10mmol/L, SC1001 Na completely blocked AP and depolarized the RP significantly. These effects were not reversible. As the structure of SC1001 Na is different from that of heterocycloguanidine Na channel blocker, such as TTX, or that of local anesthetics, we infer that SC1001 Na may be a new sodium channel blocker.

Action Potentials↗
PubMed1996

Synaptic remodeling revealed by repeated in vivo observations and electron microscopy of identified frog neuromuscular junctions.

This work aimed to examine the mechanism of synaptic remodeling using repeated in vivo observations, followed by electron microscopy, of identified frog neuromuscular junctions (NMJs). Our previous light microscopic studies suggested that extension of synaptic extracellular matrix (ECM) precedes, and may play a role in, nerve terminal (NT) growth during synaptic remodeling. To test this hypothesis, sartorius muscles were double labeled with a fluorescent dye, 4-(4-diethylamino-styryl)-N-methylpyridinium iodide, for NTs and rhodamine-conjugated peanut agglutinin for synaptic ECM. The double-labeled NMJs were observed in vivo with video-enhanced fluorescence microscopy. Two to three months after nerve sprouting was induced by a nerve graft, the same NMJs were restained and reexamined. After the final in vivo observations, the same NMJs were examined with semiserial thin section electron microscopy. Light microscopic observation of NMJs that showed synaptic ECM longer than the NT was confirmed with electron microscopy. At junctional branches where synaptic ECM extended beyond the NT, a Schwann cell process longer than the NT was observed in one example, whereas a Schwann cell with the same length as the NT was seen in other examples. In both cases, junctional folds were absent at the extended ECM region. In contrast, junctional folds were observed at the region vacated by a retracted NT. These results suggest that extension of synaptic ECM and Schwann cell processes may lead, and play a role in, the NT growth during the remodeling of adult synaptic connections.

Animals↗
PubMed1996

[A preliminary study on the hormonal causes of seasonal change in miniature endplate potentials at the neuromuscular junctions of the toad].

The hormonal causes of seasonal change in amplitudes of miniature endplate potentials (MEPP) in the adult toad (Bufo bufo gargarizans) were studied with intracellular recordings of MEPP at the neuromuscular junction of sartorius muscle fiber in vitro by adding L-thyroxine sodium and estrone to the bath medium during spring and autumn respectively. The results showed that L-thyroxine sodium (50 mumol/ L) could not change the amplitude of MEPP, regardless of spring or autumn, but estrone (100 mumol/L) could cause a clear increase in MEPP amplitude in both seasons. From these results it was presumed that thyroxine might be less related to the seasonal changes in MEPP amplitude whereas the seasonal fluctuations of gonadal hormones in the body might play a role.

Animals↗
PubMed1991

A comparative study of the supramolecular structure of frog sartorius and dorsal semitendinosus muscle.

This report describes a comparative X-ray diffraction study of the supramolecular structure of frog sartorius and semitendinosus muscles. For sarcomere lengths of 2.7 microns and below the X-ray diffraction diagrams of each muscle type are very similar; the only differences being that the diffraction diagram for semitendinosus muscles exhibit the presence of a broad diffraction band or a cluster of diffraction orders at a spacing of ca. 230.0 nm and, also, they lack a periodicity of ca. 102.0 nm. For sarcomere lengths greater than 2.7 microns disruption of the sarcomere from sartorius muscle occurs as seen by the loss of sampling in the diffraction diagram. The semitendinosus muscle can be stretched to much longer lengths (in excess of 3.0 microns) before a loss of sampling is detected. The data also shows that in the case of the semitendinosus muscle for long sarcomere lengths transverse bands of mass are able to move without retaining a defined distance to either the Z or the M lines. This is not observed in the case of the sartorius muscle. Thus, at resolutions between ca. 3.6 microns and 7.50 nm significant ultrastructural differences between these two muscles are apparent. The data suggest that the ability of these mass bands to move may be responsible for the differences in the development of passive tension exhibited by these two muscles.

Animals↗