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PubMed1982

Effects of divalent cations on toad end-plate channels.

Miniature end-plate currents (MEPCs) and acetylcholine-induced current fluctuations were recorded in voltage-clamped, glycerol-treated toad sartorius muscle fibers in control solution and in solutions with added divalent cations. In isosmotic solutions containing 20 mM Ca or Mg, MEPCs had time constants of decay (tau D) which were about 30% slower than normal. In isotonic Ca solutions (Na-free), greater increases in both tau D and channel lifetime were seen; the null potential was -34 mV, and single-channel conductance decreased to approximately 5 pS. Zn or Ni, at concentrations of 0.1-5 mM, were much more effective in increasing tau D than Ca or Mg, although they did not greatly affect channel conductance. The normal temperature and voltage sensitivity of tau was not significantly altered by any of the added divalent cations. Surface potential shifts arising from screening of membrane fixed charge by divalent cations cannot entirely explain the observed increases in tau, especially when taken together with changes in channel conductance.

Acetylcholine↗
PubMed1994

Lateral approach to femoral bifurcation.

Femoral bifurcation can be approached through a lateral incision in the femoral triangle, passing behind the sartorius muscle and thus leaving undisturbed the femoral lymphatic network. The principal advantage of this route is it limits the local complications that occasionally result in infection of the operative site. This lateral approach is indicated primarily for infrainguinal revascularizations originating from the common femoral artery in patients at high risk for local infection. It should not, however, be used routinely because exposure of the vessels, particularly the medial aspect of the artery and the profundus vessels, is limited. The risks of this route are essentially related to the neural elements encountered during dissection.

Dermatologic Surgical Procedures↗
PubMed1996

Bromoacetylcholine and acetylcholinesterase introduced via liposomes into motor nerve endings block increases in quantal size.

We incorporated bromoacetylcholine (an inhibitor of choline acetyltransferase), acetylcholinesterase, or both into liposomes made of phosphatidylcholine. Frog sartorius muscles were exposed to these liposomes for 30-60 min. The liposome treatment itself did not decrease the size of the quanta compared to untreated controls. Then the preparations were exposed for 10-20 min to a hypertonic solution, which increases the rate of spontaneous quantal release and elicits an increase in the amount of acetylcholine released per quantum. Following the hypertonic treatment the quanta were significantly smaller in the liposome-treated preparations. Most of the difference occurred because in the preparations not exposed to the liposomes quantal size increased following the hypertonic treatment. This increase is thought to be due to the incorporation of more acetylcholine into each quantum. Our conclusions are that the treatments decreased the acetylcholine concentration in the cytoplasm, and that the increase in size occurs because additional acetylcholine is added to the vesicles containing the quanta from the cytoplasm.

Acetylcholine↗
PubMed2001

Pedicle myocutaneous flaps for reconstruction following total pelvic exenteration of intrapelvic recurrent rectal cancer: report of a case.

A vast metastatic tumor mass of recurrent rectal carcinoma in the intrapelvic organs is commonly considered unsuitable for total pelvic exenteration (TPE); first, because it is unlikely that it would improve the prognosis and health-related quality of life of the patient, and second, because of the difficulties involved in this surgical technique. However, by using a plastic surgery technique involving reconstruction by filling the pelvic dead space with pedicle myocutaneous flaps (PMF), primary wound closure and extensive resection of the perineum can be achieved, whereby postoperative metastasis may be prevented. We report herein the case of a 71-year-old man found to have local recurrence in the perineum with extensive invasion of the soft tissue as well as adjacent organs, 20 months after abdominal perineal resection for rectal carcinoma. TPE with extensive resection of the perineal soft tissue was performed, followed by perineal reconstruction and packing of the pelvic dead space with PMF, mainly constructed from the gracilis and sartorius muscles of both femurs. His postoperative course was uneventful and he has remained free of local recurrence and symptomatic perineal complaints for 1 year. In this report, we examine the effectiveness of using the gracilis muscle for PMF in intrapelvic and perineal reconstruction after TPE.

Adenocarcinoma↗
PubMed1977

A new solid-state microelectrode for measuring intracellular chloride activities.

Solid-state microelectrodes from measuring intracellular Cl activity (alphaiCl) were made by sealing the tips of tapered glass capillaries (tip diameter 0.3 mum), coating them under vacuum with a 0.2-0.3 mum thick layer of spectrscopic grade silver, and sealing them (except for the terminal 2-5 mum of the tip) inside tapered glass shields. 106 microelectrodes had an average slope of 55.0+/- 0.6 m V (S,E,) per decade c hange in alphaCl. Tip resistance was (77.1+/- 3.1) x 10(9) omega(n=30). Electrode response was rapid (10-20 s), was unaffected by HCO3, H2PO4, HPO42 or protein, and remained essentially unchanged over a 24-h period. AlphaiCl in frog sartorius muscle fibers and epithelial cells of bullfrog small intestine was measured in vitro. In both tissues, alphaiCl significantly exceeded the value corresponding to equlibrium ditribution of Cl across the cell membrane.

Animals↗
PubMed1984

On the interaction of cobra venom protein cardiotoxins with erythrocytes.

The principally active hemolytic toxin (cardiotoxin) previously purified from the venom of the Thailand cobra, Naja naja siamensis, was shown to produce spontaneous twitching, contractures and membrane depolarization in sartorius muscles from the frog, Rana pipiens. Spontaneous twitching, observed at concentrations greater than 0.1 uM was completely abolished by addition of tetrodotoxin and not affected by d-tubocurarine. Dose and time dependent membrane depolarization of muscle fibers was observed to occur within 10-30 min at 0.2 to 1.0 uM concentrations of the toxin. These observations, taken together with an amino acid analysis characteristic of previously described cobra venom cardiotoxins, characterized this hemolytic toxin as a cardiotoxin. In the absence of EDTA the initial velocities of erythrocyte hemolysis for this toxin showed a sigmoidal concentration dependence which became hyperbolic in the presence of EDTA. The largest increases in hemolysis rates on addition of 1 mM EDTA were observed at low toxin concentrations. In the presence of EDTA extracellular and membrane associated divalent cations are complexed, thus alleviating their competition with toxin for binding to the membrane, a key and apparently rate-determining initial step which leads to hemolysis. In the presence of EDTA hemolysis rates increased linearly at low toxin concentration and reached an extrapolated maximum value at toxin concentrations at which, given its molecular dimensions, there are just sufficient toxin molecules to cover the entire membrane surface area provided by the erythrocytes.

Animals↗
PubMed1983

The effect of streptomycin on the neuromuscular junction of the frog.

The neuromuscular block produced by streptomycin was studied in the frog sartorius muscle by means of intracellular recording and iontophoretic application of acetylcholine. Decreases of the end-plate potentials (e.p.p.s) and acetylcholine potentials (ACh potentials) were observed following the application of streptomycin. At a concentration of 10(-4) M, the e.p.p. was 36.8 +/- 5.5% (mean +/- S.E.) (n = 12), and the ACh potential was 53.7 +/- 3.8% (n = 12) of the control size. The resting membrane potential and membrane conductance of the muscle fibers were not affected by streptomycin. Streptomycin did not significantly alter the spontaneous prejunctional activity, but the amplitude of the miniature end-plate potentials (m.e.p.p.s) was decreased. After the application of higher concentrations of streptomycin, the quantum content decreased from the control value. It is suggested that the reduction of the e.p.p. amplitude produced by streptomycin is mainly due to a decrease in the sensitivity of the end-plate membrane. In addition, at higher concentrations, streptomycin reduced the amount of transmitter released from the motor nerve in response to a nerve volley.

Animals↗
PubMed1985

Distribution of exponentiality in miniature endplate current decay.

Exponential functions are commonly used to describe miniature endplate current (MEPC) decay; under control conditions a monoexponential is usually regarded as sufficient, whereas in the presence of some drugs a biexponential may be necessary. Using an automated fitting procedure which estimated exponential parameters and the period of decay from peak to baseline, a unimodal distribution of curvature was found for control MEPCs recorded in frog sartorius muscle. The majority of MEPCs were of monoexponential form, while the remainder were biexponential with either less or greater curvature than expected for a simple exponential (hypoexponential or hyperexponential, respectively). The proportion of MEPCs in each of the 3 groups was constant for a given endplate but varied between endplates. A possible explanation for this phenomenon could be differences in synaptic geometry within and between endplates. The increased curvature of individual MEPCs in the hyperexponential group was analyzed by assuming a sequential model for agonist blockade or desensitization, and calculating closing and reopening rate constants. These rate constants were altered by procaine and verapamil (100 microM) in a manner consistent with blockade of the acetylcholine receptor by enhancement of agonist-induced desensitization.

Animals↗
PubMed1988

Acceleration by stannous ion of the evoked release of transmitter from motor nerve endings in the frog.

Stannous ion (Sn2+, 30 microM) increased the amplitude of endplate potential (EEP) in the frog sartorius muscle, although the amplitude of miniature endplate potential (MEPP) or acetylcholine potential evoked by iontophoretic application of acetylcholine was unchanged. Sn2+ (10-100 microM) dose-dependently increased the quantal content of the EPP. MEPP frequency was not altered by 30 microM Sn2+. These findings indicate that Sn2+ may increase the EPP as a result of acceleration of the transmitter release evoked by nerve impulses.

Acetylcholine↗
PubMed1989

Seasonal changes in the normal variability in release properties of motor nerve terminals in Rana pipiens.

During a 2 1/2 year period, we studied 298 identified endplates from 40 sartorius muscles, correlating their morphology with their synaptic release properties. There is a remarkably large range in evoked and spontaneous quantal release levels when junctions are studied in a low-Ca2+ Ringer. This diversity in release efficacy persists when release is normalized to identified nerve terminal length. We also found that release was significantly larger in the winter (Dec-Feb) than in the spring and summer (Mar-Aug), suggesting seasonal regulation of release properties.

Animals↗
PubMedDate not supplied

Structural aspects of the effect of ethyl benzoates on caffeine contracture.

The effect of ethyl benzoate, ethyl o- and p-fluorobenzoate and ethyl o- and p-toluate on the caffeine-induced contracture of frog sartorius muscle was investigated. All drugs with the exception of ethyl o-toluate depressed caffeine-induced contractures. It is proposed that the methyl group in ethyl o-toluate sterically blocks the ester carbonyl group from exerting its inhibitory action. It is further proposed that ethyl o-aminobenzoate exerts its potentiating effect through the lone pair of electrons on the nitrogen atom.

Animals↗
PubMed1978

Calcium-dependent inhibition by prostaglandin E1 of spontaneous acetylcholine release from frog motor nerve.

PGE1 (10(-7) M) in the absence of Ca2+ or at low external Ca2+ concentrations (0.2-0.5 mM) depressed the frequency of miniature end-plate potentials (m.e.p.p.s) in frog sartorius muscle, but m.e.p.p. amplitudes were unchanged. Both an increase in Ca2+ concentration to 2 mM or a blockade of Ca2+ uptake into mitochondria by metabolic inhibitors (5 X 10(-5) M 2,4-dinitrophenol or 2 X 10(-5) M rotenone) prevented the inhibitory action of PGE1 on m.e.p.p. frequency. We suggest that PGE1 may inhibit acetylcholine release from motor nerve terminals by promoting the active uptake of Ca2+ by mitochondria, or by facilitating the efflux of Ca2+ from the axoplasm into the extracellular medium.

Acetylcholine↗
PubMed1980

The effects of 3,4-diaminopyridine on acetylcholine release at the frog neuromuscular junction.

The effects of 3,4-diaminopyridine (3,4-DAP) were studied on spontaneous and evoked transmitter release in the frog sartorius muscle preparation. At a concentration of 1 mM, 3,4-DAP caused the appearance of spontaneous giant potentials, this effect of 3,4-DAP also occurred in absence of extracellular calcium. At lower concentrations in magnesium Ringer 3,4-DAP (1-10 microM) increased e.p.p. quantal content without causing the appearance of spontaneous giant potentials, 3,4-DAP prolonged muscle action potential (1 mM) and it is suggested that prolongation of the nerve terminal action potential by 3,4-DAP contributes largely to the increased evoked acetylcholine release. The ability of 3,4-DAP to cause the appearance of giant spontaneous potentials is considered to be independent of the drug's known ability to inhibit potassium conductance in excitable membranes, and may be due to the release of performed multiquantal packets of acetylcholine as suggested for vinblastine. It is concluded that 3,4-DAP is a useful tool in the study of both evoked and spontaneous acetylcholine release.

4-Aminopyridine↗
PubMed1985

Effects of aniline on neuromuscular transmission.

Aniline hydrochloride increased the amplitude of the end-plate potentials of the frog sartorius muscle. Statistical analysis showed that the effects of aniline were purely presynaptic. The shape of the dose-release curve was similar to that of the 4-aminopyridine curve although the potency was weaker than that of 4-aminopyridine. The molecular configuration and the effect of aniline suggested that the site of action of aniline was the same as that of 4-aminopyridine.

4-Aminopyridine↗
PubMed1986

Effects of memantine on the frog neuromuscular junction.

The effects of memantine, an adamantane derivative, on neuromuscular transmission in the frog sartorius muscle preparation were studied by measuring the endplate current (EPC) by the voltage clamp method. Memantine (0.5-50 microM) reduced the peak amplitude and shortened the duration of the EPC, and the membrane voltage-peak EPC relationship became non-linear. Since it decreased the quantal height of the EPC without affecting the mean quantal content, the effects were considered to be mainly postsynaptic. Noise analysis revealed that memantine decreased the mean lifetime of the ACh-activated channel. In addition, lineweaver-Burk analysis of the response to ionophoretically applied carbamylcholine showed that memantine acted essentially as a linear mixed-type inhibitor. Thus memantine seems to block neuromuscular transmission by reacting with the ACh receptor-ion channel complex in both the open and closed states.

Acetylcholine↗
PubMed1987

Interaction of narcotic antagonist naltrexone with nicotinic acetylcholine receptor.

The interactions of naltrexone with the nicotinic acetylcholine receptor were studied electrophysiologically using the frog sciatic nerve-sartorius muscle and biochemically using membranes from the electric organ of Torpedo ocellata. At nanomolar concentrations naltrexone increased the peak amplitude of endplate currents with little change in the decay time constant. At micromolar concentrations there was a concentration-dependent depression of endplate current and miniature endplate current amplitudes and decay time constants. Decay time constant depression was enhanced with hyperpolarization. Only marginal curvature was induced in peak endplate current amplitude versus membrane voltage plots by naltrexone. Naltrexone had no effect on single channel conductance but decreased open channel lifetime, according to fluctuation analysis. Naltrexone alone (less than or equal to 3 microM) did not impair binding of [125I]alpha-bungarotoxin to the receptor in a fast pre-equilibration assay, but increased the ability of acetylcholine to displace [125I]alpha-bungarotoxin. The drug displaced the agonist-stimulated binding of [3H]perhydrohistrionicotoxin to the channel site. Biphasic functional changes in neuromuscular transmission can be attributed to an allosteric mechanism with increased agonist binding to the nicotinic receptor at nanomolar concentrations and caused a non-competitive blockade of the ionic channel at micromolar concentrations.

Amphibian Venoms↗
PubMed1988

Neuromuscular blocking action of two hemicholinium-3 analogs.

Two hemicholinium-3 (HC-3) analogs (NAM-204 and NAM-224) in which the C = O moiety was reduced to -CH2 and 2- or 3-CH3 substitution on the piperidine ring were demonstrated to produce a different type of neuromuscular inhibition than that induced by HC-3. The neuromuscular blocking activity was tested in several different preparations and it was shown that these compounds are potent, short-acting, and was reversed by neostigmine but not by choline. Although these compounds possess weak anticholinesterase activity, significant alterations of blood pressure and heart rate are absent. Miniature end-plate potentials' amplitude were found to be diminished by these compounds with some alteration of frequency. In voltage-clamped frog sartorius muscle NAM-224 and NAM-204 decreased amplitude of miniature end-plate current (mepcs) and accelerated the time constant of mepc decay in a concentration-dependent manner, without altering the single exponential nature of mepc decay. NAM-204 and NAM-224 at high concentrations also produced a voltage- and concentration-dependent non-linearity in current/voltage relationships, especially at more negative membrane potentials. Hence, these pharmacological and electrophysiological studies indicate NAM-224 and NAM-204 have significant activity at both pre- and post-junctional sites and their post-junctional blocking activity results from blocking ACh receptor/ion channel complex.

Action Potentials↗