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At least 1,171 records · Page 65Linked to original sources
PubMed1979

Effects of two synaptic activators, calcium and ethanol, on MEPP distribution in time.

Miniature end-plate potentials (MEPPs) were recorded intracellularly from sartorius muscle of Rana esculenta. Tracings were divided into time bins whose duration approximated one-fifth of the mean interval between consecutive potentials. The observed number of bins containing 0, 1, 2, ... MEPPs was compared, by the X2 test, with the number calculated from the Poisson equation. MEPP timing was analyzed in the absence as well in the presence of Ca2+ (1 mM, 2.5 MM, and 15 mM). In half of the experiments, 0.5% ethanol was added to the bathing solution. In the absence of Ca2+, MEPP timing fitted the Poisson predictions. On adding Ca2+, the fit became poor and MEPPs showed the tendency to cluster. At 15 mM Ca2+, no experiment proved to be Poissonian. Though increasing the frequency of MEPPs similarly to Ca2+, ethanol maintained a Poissonian release of transmitter at any concentration of Ca2+. It is suggested that ethanol masks the effects of Ca2+ on MEPP timing by also inducing the discharge of transmitter outside the Ca2+-dependent sites of exocytosis in the presynaptic membrane.

Animals↗
PubMed1992

Role of myogenic response in enhancing autoregulation of flow during sympathetic nerve stimulation.

The effect of sustained sympathetic nerve stimulation on autoregulation of blood flow was examined in the exteriorized cat sartorius muscle using intravital microscopy. Without sympathetic nerve stimulation (SNS), second-order arterioles showed insignificant dilation (3%) during arterial pressure reduction from 110 to 60 mmHg; volume flow fell coincident with pressure reduction. During SNS, these arterioles constricted significantly (25%), and their dilation during pressure reduction (20%) was significant and was significantly greater than that without SNS. Volume flow increased significantly (20-60%) during pressure reduction, a phenomenon termed superregulation of flow. Elevation of ambient oxygen in the suffusate from 0 to 20% caused arteriolar constriction but did not abolish arteriolar dilation during pressure reduction under sustained SNS. Arteriolar response to venous pressure elevation was also affected significantly by sustained SNS. Without SNS, third-order arterioles showed slight dilation (4%) when femoral venous pressure was elevated by 10 mmHg. During SNS, these arterioles constricted significantly and constricted further (20%) when venous pressure was elevated. Using a local anesthetic (lidocaine), we determined that a local venous-arteriolar reflex was not involved in the arteriolar constriction. Our data suggest that superregulation of flow during sustained sympathetic nerve stimulation is not due to metabolic factors but rather to an enhanced myogenic response.

Animals↗
PubMed1992

Mechanism of enhanced myogenic response in arterioles during sympathetic nerve stimulation.

In a previous study we found that the arteriolar myogenic response was enhanced during sympathetic nerve stimulation in the cat sartorius muscle. In this study we determined whether the enhancement was unique to sympathetic nerve stimulation. Changes of arteriolar diameter and red cell velocity during femoral arterial pressure reduction from 110 to 60 mmHg were examined. Arterioles of 40 microns diameter were constricted by norepinephrine infusion to a similar degree as sympathetic nerve stimulation. Arteriolar dilation to pressure reduction was significantly enhanced during norepinephrine infusion and was not significantly different from that during sympathetic nerve stimulation. This indicates that junctional release of transmitters is not essential and rules out prejunctional inhibition of neurotransmitter release during pressure reduction as a significant mechanism in the enhanced dilation. Arteriolar dilation to pressure reduction was also enhanced during vasopressin or BAY K 8644 (a calcium channel agonist) infusion. In all instances, autoregulation of flow was significantly enhanced. These results demonstrate that modulation of the myogenic response occurs at postreceptor sites in the smooth muscle cell.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1993

Evidence for sensing and integration of biological signals by the capillary network.

The aim of this study was to explore the phenomenon first described by Dietrich (Microvasc. Res. 38: 125-135, 1989) in which a local application of norepinephrine (NE) on a capillary can temporarily reduce flow via constriction of the feeding arteriole. Our objectives were to show that this phenomenon of remote response is not limited to vasoconstriction, can be elicited by materials other than NE, shows stimulus-strength dependency, and can be integrated within the capillary network. We used an intravital micropharmacological approach to iontophoretically apply (in mM concentrations in the pipette) NE, acetylcholine (ACh), 5'-N-ethylcarboxamidoadenosine (NECA, adenosine analogue), K+, and H+ on capillaries of the frog sartorius muscle in situ. Responses were measured in terms of changes in velocity of red blood cells (VRBC) in capillaries or in terms of changes in arteriolar diameter. ACh (3 mM) caused significant increases in diameter (from 34 to 37 microns) and in VRBC (from 250 to 340 microns/s, i.e., 36%). NE (3 mM) reduced VRBC by 16%. The magnitude of ACh and NE velocity responses increased with increasing pipette concentration and with increasing iontophoretic current. The ACh response was blocked by a local pretreatment with atropine. NECA, K+, and H+ caused 20-40% increases in VRBC. Dual application of NE on two capillaries fed by the same arteriole resulted in a greater VRBC reduction than for single NE application. Dual application of NE and ACh significantly attenuated the ACh response.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1975

Non-Poisson distribution in time of small- and large-mode miniature end-plate potentials.

Minature end-plate potentials (MEPP's) were recorded from frog (Rana pipiens) sartorius muscle cells of 60--80 mum diam; MEPP frequency remained constant up to 3 h and was 100 times greater in 80-mum cells than in 6-mum cells. Rapid cooling or heating of preparations initiated or accentuated bursts of MEPP's. Records from cells under control conditions and from cells where the MEPP population had been reduced to the small mode showed many instances of small clusters of MEPP's occurring within 100-ms intervals, indicating quantal release interdependencies. Some small cells initially generated many large MEPP's 2 or more times the average amplitude and fewer small clusters. Analysis of the occurrence of both large- and small-mode MEPP's for both 1.0-s and 100-ms nonoverlapping bins demonstrated a highly significant deviation from a Poisson distribution with significance increasing with decreasing cell diameter and/or MEPP frequency. It is suggested that doublet MEPP's are generated from one release site and that large bursts results from the activity of several release sites, since the size of bursts decreases with cell diameter (junctional area). It is concluded that release characteristics are the same for large-mode (classical) and small-mode MEPP's and that the occurrence of MEPP's is not Poisson.

Animals↗
PubMed1976

Elastic modulus and stress relationships in stretched and shortened frog sartorii.

The longitudinal dynamic elastic modulus (delta stress/delta strain) of 11 sartorius muscles (Rana pipiens; 3 degrees C) was measured at static strains, 0.57 less than L/Lo less than 1.53. Pseudorandom white-noise displacements less than +/-0.031% Lo (mean, peak to peak) were imposed on tetanically stimulated and resting muscles to obtain the isometric moduli. The active elastic modulus at each length was determined as the difference between the low-frequency (15-80 Hz) asymptotes of the tetanic and resting modulus functions. Resting moduli were found to increase with stretch at a declining rate, suggesting that some resting elasticity is attributable to active crossbridges. For isometric, tetanically stimulated muscles above L/Lo = 1.0, the ratio dynamic elastic modulus/active stress was nearly constant (65.4); the data predict zero modulus at a stretched length corresponding to zero active stress. Hence, the modulus per crossbridge exhibits sarcomere length invariance. On the other hand, active muscles below L/Lo = 0.77 manifest a significant (P less than or equal to 0.05) additional modulus beyond that found at the same active stress in the stretched muscle. Sarcomeric structural rearrangements are suggested as a possible source of this additional modulus.

Animals↗
PubMed1985

Effects of hypocalcemia on diaphragmatic strength generation.

We studied the effects of hypocalcemia on diaphragmatic force and diaphragm blood flow (Qdi) in 12 anesthetized dogs. The diaphragm was electrically stimulated with intramuscular electrodes surgically implanted in the ventral surface of each hemidiaphragm. The transdiaphragmatic pressure (Pdi) during supramaximal (50 V) 2-s stimulations applied over a frequency range of 10-100 Hz was measured with balloon catheters during tracheal occlusion at functional residual capacity. A catheter was placed via the femoral vein into the left inferior phrenic vein, and Qdi was measured by timed volume collections of left inferior venous effluent. A catheter was introduced in a femoral artery to monitor blood pressure (BP). In five additional dogs, the force generated by the sartorius muscle during electrical stimulation was also studied concomitantly to diaphragmatic force. The animals were mechanically ventilated throughout the experiment, and the arterial blood gases and pH were maintained constant. Hypocalcemia was induced by a continuous infusion of EGTA (70 mg X kg-1 X h-1), which led to a progressive decrease (P less than 0.0001) of ionized calcium plasmatic level from 2.21 +/- 0.4 meq/1 during control to 1.69 +/- 0.06, 1.25 +/- 0.5, and 1.07 +/- 0.5 meq/1 after 30, 60, and 120 min, respectively. Hypocalcemia decreased progressively Pdi, which amounted to 84 +/- 3 (P less than 0.001) and 98 +/- 2% of control values for the low frequencies (10 and 20 Hz) and the high frequencies (50 and 100 Hz), respectively, after 30 min of EGTA infusion and to 74 +/- 5 and 79 +/- 6% for the low and high frequencies, respectively, after 120 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Pretreatment with hypertonic solutions increases quantal size at the frog neuromuscular junction.

Miniature end-plate potentials (MEPPs) are increased in size by pretreatment in a hypertonic Ringer. This paper is about the treatments that increase quantal size and the evidence that it occurs by packing more acetylcholine (ACh) in the quanta. Sartorius muscles were soaked for 2 h in a hypertonic Ringer, containing 200 mM NaCl in place of the usual 120 mM, and then returned to Ringer. In the hypertonic solution the miniature frequency was above 100/s. The treatment increased the size of the miniatures, recorded with an intracellular electrode after the return to usual Ringer, by a factor of approximately 2.5, compared with paired muscles kept in usual Ringer throughout. When the hypertonic solution was made with 200 mM sodium gluconate, after the return to usual Ringer, the miniatures increased in size by a factor of approximately 3.6. The large miniatures produced by the treatment fit a log normal probability distribution function, except for a variable small fraction of the largest events that may represent multiple releases. Miniatures recorded from untreated end plates fit better to a log normal distribution function than to a normal distribution function. The effects of the hypertonic treatments on the acetylcholine receptor (AChR) were accessed by measuring, after the return to usual Ringer, ACh noise, alpha-bungarotoxin binding, and the reversal potential. None of these measurements revealed significant differences between experimental and control preparations. The increases occurred when neostigmine was present in the hypertonic and usual solutions and when it was not, so changes in acetylcholinesterase (AChE) do not appear to be involved. Both the MEPPs and miniature end-plate currents, recorded with the two electrode voltage clamp, increased in size, so the increase is not owing to an rise in the input resistance of the muscle fiber. The increase in quantal size was prevented by including 1-10 microM AH5183 in the hypertonic solution. This drug blocks ACh uptake into synaptic vesicles. Therefore, it seems likely that the treatments act by increasing the quantity of ACh/quantum. Cyclohexamide (10 micrograms/ml), an inhibitor of protein synthesis, did not affect the increase in size caused by hypertonic solutions. Size increases were detected after 15 min in hypertonic solution. Most of the increase was complete after 1 h and there was no further increase after 2 h.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine↗
PubMed1981

Monensin toxicosis in broiler chickens.

Chickens treated at seven weeks of age with 150, 200, or 250 mg of crystalline monensin sodium/kg body weight had signs of toxicosis, including extreme weakness, anorexia, paralysis and death. Gross lesions included emaciation, generalized congestion, myocardial enlargement and pallor, and hydropericardium. Samples of ventricular myocardium, superficial pectoralis (white fibers), anterior latissimus dorsi (intermediate fibers), and sartorius muscles (mixed red, intermediate, and white fibers) were examined by light microscope. Intermyofibrillar vacuolation, histochemically positive for neutral fat, was severe in the myocardium and red muscle fibers and moderate in the intermediate muscle fibers. Myofiber necrosis was limited to the red muscle fibers. Mitochondrial degeneration was apparent in myocardial sections from several chickens. Interstitial infiltration by macrophages and heterophils was common in the myocardium and aerobic skeletal muscle.

Animals↗
PubMedDate not supplied

The saphenous nerve: its course and importance in medial arthrotomy.

Both lower extremities of 10 cadavers (20 specimens) were dissected to delineate the course of the saphenous nerve and its two major divisions (sartorial and infrapatellar branches). The course of the saphenous nerve followed the standard text description, except at the point in the sartorius muscle where the infrapatellar branch exited to become a subcutaneous structure. The location of this branch varied slightly in each cadaver but was the same for both lower extremities in the same cadaver. The location of the sartorial nerve and its relationship to the tendons of the pes anserinus was consistant in all 20 specimens. Since 69% of a group of 75 patients found altered sensation significant after routine sectioning of the infrapatellar nerve following medial meniscectomy, a group of surgeons at the University of Michigan is now protecting the infrapatellar branch of the saphenous nerve at operation. Early results on a small number of patients indicate that no alteration in sensation occurs if the nerve is carefully retracted.

Cadaver↗
PubMed1985

Immunological localization and quantitation of the androgen-dependent secretory protease of the canine prostate.

We have recently reported on the isolation and characterization of the predominant protein of canine prostatic fluid and the subsequent identification of this protein as a proteolytic enzyme. In this report, we described the preparation and characterization of a rabbit antiserum against this secretory protease which was purified from canine prostatic fluid by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Specificity of the antiserum has been established by immunoblot analysis and immunoprecipitation of the secretory protease present in canine prostatic fluid and tissue homogenates. The antiserum was used to localize (by immunofluorescence) and quantitate (by single radial immunodiffusion) the secretory protease in prostatic tissue obtained from intact and castrated dogs. These analyses can be summarized as follows: the secretory protease is strictly localized in the apical portions of the columnar epithelial cells in prostates of intact dogs, where it comprises almost 60% of the total Triton X-100-soluble protein; and the level of secretory protease decreases at least 500-fold in prostates of castrated dogs, demonstrating the androgen-dependent nature of this enzyme. Proteins immunologically related to the secretory protease were detected at low levels in the pancreas and salivary glands of the dog. Such proteins were not detectable in canine liver, kidney, vas deferens, testis, epididymis, lung, spleen, skin, small intestine, or sartorius muscle, suggesting a high degree of prostatic specificity for the secretory protease. These results demonstrate that the canine prostate is highly specialized with respect to its androgen-dependent synthesis and secretion of this secretory protease and that the antiserum specific for this protein can be used to assess canine prostatic function under varying hormonal conditions.

Animals↗
PubMedDate not supplied

Comparative neuromuscular effects of lincomycin and clindamycin.

The effects of lincomycin and clindamycin on neuromuscular transmission in vitro were studied. Standard microelectrode technics were used to measure miniature endplate potential (MEPP) amplitude and frequency, and endplate sensitivity to acetycholine on the frog sartorius muscle. Twitch tension and nerve terminal acetycholine release were also studied. In the drug concentration range where twitch tension changes occurred, both drugs caused marked decreases in MEPP amplitude and decreases in endplate sensitivity to iontophoretically applied acetylcholine. Lincomycin did not alter MEPP frequency but decreased acetylcholine release. Clindamycin increased MEPP frequency and increased acetylcholine release. The study shows that both lincomycin and clindamycin cause blockade of neuromuscular transmission through a postsynaptic action. However, at high concentrations, lincomycin has a nerve-terminal depressant effect, while clindamycin has a marked presynaptic stimulatory effect.

Acetylcholine↗
PubMed1994

THERMAL ACCLIMATION, NEUROMUSCULAR SYNAPTIC DELAY AND MINIATURE END-PLATE CURRENT DECAY IN THE FROG RANA TEMPORARIA

1. The effects of 1 or 2­3 weeks of acclimation to 4 °C and 24 °C of overwintering grass frogs (Rana temporaria) on the synaptic delay and on the time constant of the decay phase (tau) of miniature end-plate currents (MEPCs) in the neuromuscular junction of sartorius muscle were studied. In order to equalize the possible effects of differential starvation, the animals were usually cross-acclimated to the two temperatures. 2. Synaptic delay was not affected by temperature acclimation but was slightly prolonged by the more profound starvation at the higher temperature when the cross-acclimation procedure was not used. The average Q10 of synaptic delay between 4 and 24 °C was 2.60 and of minimum synaptic delays, 2.64. The corresponding values for apparent activation energy (Ea) were 65.79 and 66.48 kJ mol-1. 3. The time constant of the decay phase of MEPCs was not affected by temperature acclimation. The average Q10 between 4 and 24 °C was 2.27. The corresponding Ea value was 56.02 kJ mol-1. 4. The function of peripheral neuromuscular synapses is well regulated and changes in its time relationships do not appear to be involved in the thermal acclimation of frogs.

Journal Article↗
PubMed1976

Comparison of local anesthetic activities between cis and trans isomers of DL-1-benzoyloxy-2-dimethylamino-1,2,3,4-tetrahydronaphthalene.

The local anesthetic activities of cis- and trans- dl-1-benzoyloxy-2-dimethylamino-1,2,3,4-tetrahydronaphthalene were compared using several methods with guinea-pigs. The cis compound (YAU-17) was 2.9 to 6 times as potent as its trans isomer and exceeded procaine, lidocaine and cocaine in potencies of corneal anesthesia, intracutaneous anesthesia and sciatic nerve block. In another experiment on isolated frog sartorius muscle, all of the local anesthetics suppressed the twitch contractions elicited by stimulation of the sciatic nerve. The neuromuscular blocking activity of the cis compound was more pronounced than that of the trans form. Supersensitivity to noradrenaline was produced by both of the stereoisomers in isolated vas deferens of guinea-pigs although there was no difference in the activity. The sensitizing action was also demonstrable with cocaine and lidocaine but not with procaine. When injected intravenously into mice, the cis compound was twice as toxic as its isomer. It is postulated that stereoselectivity is to some extent involved in the mechanisms of action of the local anesthetic agents.

Anesthetics, Local↗
PubMed1984

Blocking effects of blended paeoniflorin or its related compounds with glycyrrhizin on neuromuscular junctions in frog and mouse.

The combined effects of paeoniflorin (PF), a main component of paeony roots, and glycyrrhizin (GLR), a main component of licorice roots, were investigated on isolated sciatic nerve-sartorius muscle preparations in frogs, or on isolated or in situ phrenic nerve-diaphragm muscle preparations in mice, intending to explain the effects of "Shakuyaku-Kanzô-Tô, composed of both these Chinese drugs, on clinical neuropathy. PF and GLR used together blocked indirectly stimulated twitchings at concentrations which when used alone induced no blocking effects. PF and GLR at a combining ratio of 1:2 (weight concentrations) corresponding to the amounts contained in "Shakuyaku-Kanzô-Tô, was more potent than when they were used at the ratio of 1:1 or 2:1. The synergistic effects induced by GLR were also confirmed for the other components, paeoniflorigenone or oxypaeoniflorin, which are contained in paeony roots, and for succinylcholine. The blocking effect of d-tubocurarine were not increased by GLR. Concludedly, PF and GLR were found to cause the pharmacological blend effect. The two combined compounds were mainly therapeutic components in "Shakuyaku-Kanzô-Tô".

Animals↗
PubMed1975

Sarcolemmal slow conductance increase of frog sartorius fibers during hyperpolarization.

The properties of the hyperpolarization-activated sarcolemmal slow conductance increase in frog sartorius muscle fibers have been investigated using ethylenediaminetetraacetic acid disodium salt (EDTA) and propionate Ringer solution. More than 1 sec was required for maximum activation of the sarcolemmal slwo conductance increase. It is suggested that, although the sarcolemmal slow conductance increase was affected by deterioration, the conductance increase is not a direct product of deterioration but it represents a property of the sarcolemma which is encountered in physiological range. The sarcolemmal conductance increase was rather insensitive to the change in pH of Ringer solution. It is inferred that the absence of bellying in newly penetrated intact fibers at neutral and alkaline pHs is caused mainly by the shunting effect of large parallel conductance. Apparent augmentation with EDTA of the sarcolemmal conductance increase infers that Ca ions affect the conductance increase. The conductance increase occurred also in the EDTA-containing Cl-deficient solution. The sarcolemmal slow conductance increase has been compared with the change in Cl conductance reported by Hutter and Warner, and Warner.

Animals↗
PubMed1982

Intracellular measurement of Na activity using neutral carrier Na ion-selective microelectrode.

To measure intracellular Na+ activities, a double-barreled Na ion-selective microelectrode was constructed with a neutral carrier Na+ ligand (ETH 227). The slope constant and detection limit were 56 mV and 3-5 mM, respectively, the selectivity of Na+/K+ being 40-50. In the bullfrog, the cell Na+ was 14.4 mEq/liter for the proximal tubule and 12.6 mEq/liter for the sartorius muscle.

Animals↗
PubMed1983

Catechol and noradrenaline facilitate the neuromuscular transmission via different mechanisms.

Using curarized frog sartorius muscles, selective presynaptic facilitatory effects of two structurally related chemicals, noradrenaline (NA) and catechol (pyrocatechol, PC), were compared by calculating the fractional release (P) from the rundown of endplate potential during a train-of-three stimulation. Below 10 microM, both NA and PC increased P in a similar manner. At higher concentrations, however, the effects of NA were found to be quite different from those of PC. NA never increased further the value of P (0.11-0.13) whereas PC augmented P in a dose dependent fashion up to about 0.76. Thus, the present data suggested that NA and PC facilitate the transmitter release via different mechanisms. The effects of the latter were identical to the case of "chemical potentiation or accelerated evoked release" by 4-aminopyridine.

Animals↗