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PubMed1961

Effects of drugs on partially and completely denervated skeletal muscle of the frog.

The sensitivity of completely denervated and the innervated end-plate regions of partially denervated frog's sartorius muscles to stimulation by drugs has been investigated. The drugs were tested on muscles isolated 12 to 39 days following denervation. On the basis of the results obtained most of the drugs could be put into one of two main groups. The first group included choline, tetramethylammonium, carbachol and decamethonium; these drugs readily stimulated non-denervated muscles, and chronic denervation, either partial or complete, greatly increased the sensitivity of the muscles. The second group included pilocarpine and carbamate of (2-hydroxypropyl) trimethyl ammonium chloride (Bethanechol, U.S.P.). The muscles were relatively insensitive to stimulation by these two drugs. They could stimulate the muscles if applied in high enough concentrations, but the responses thus obtained could not be distinguished from responses produced by similar concentrations of sucrose and chronic denervation did not increase the sensitivity of the muscles to stimulation by these two drugs. Methacholine, like the drugs in the second group, was unable to stimulate the muscles in low concentrations, but chronic denervation rendered the muscles sensitive to stimulation by this drug. Tetraethylammonium presented a completely different pattern of activity which was consistent with a hypothesis that in low doses this drug stimulates skeletal muscle by causing a release of acetylcholine from nerve endings in the muscle.

Acetylcholine↗
PubMed1962

A comparison of the responses of the tenuissimus muscle to neuromuscular blocking drugs in vivo and in vitro.

In view of the differing responses to decamethonium which have been reported for the isolated tenuissimus muscle on the one hand and the tibialis muscle of the cat on the other hand, the responses of the tenuissimus muscle to neuromuscular blocking drugs were studied both in vivo and in vitro and compared with those of the tibialis anterior muscle. In both muscles in vivo, the block produced by decamethonium had all the well-known characteristics of blockade due to long-lasting depolarization, independent of the number of doses given. However, when the tenuissimus muscle was studied in vitro its responses were considerably altered. When decamethonium was left in contact with the isolated muscle, maximum paralysis developed quickly, but then the muscle recovered despite the continued presence of the drug in the bath. This contrasts with the effect obtained in vivo, where a steady application of decamethonium produced steady blockade. This spontaneous recovery in vitro occurred to a smaller extent with each successive dose. In addition, the usual antagonism between depolarizing and competitive drugs was only seen during the earlier part of an experiment and rarely occurred after several doses. It is suggested that the differences between in vivo and in vitro responses of the tenuissimus muscle to decamethonium could be due to detrimental changes in ionic concentration gradients resulting from immersion in an artificial fluid.

Animals↗
PubMed1969

Effects of ganglion blocking agents on nicotine extensor convulsions and lethality in mice.

1. The ganglion blocking agents, chlorisondamine, pentamethonium, mecamylamine, decamethonium and hexamethonium all block nicotine extensor convulsions when administered intraventricularly in mice. Tetraethylammonium was inactive.2. For the intraventricular route, there is a relationship between ganglionic blocking potency and blocking of nicotine extensor convulsions. Indirect evidence suggests that the site(s) of action of nicotine extensor convulsions and lethality is central in origin and associated with brain areas near the ventricles.3. When ganglion blocking agents are given orally, subcutaneously or intravenously varying degrees of protection can be observed probably depending on factors such as whether or not the drugs cross the blood-brain barrier, absorption, etc., and the effectiveness in protecting mice from nicotine is not related to ganglionic blocking potency.4. Atropine and morphine given intraventricularly or subcutaneously did not protect mice from the LD95 of nicotine. Chlorpromazine gave very erratic results and phenobarbitone was effective subcutaneously and to a lesser extent intraventricularly.

Animals↗
PubMed1969

The pharmacology of the cholinoceptor in muscle preparations of Ascaris lumbricoides var. suum.

1. The preparation of a muscle strip of Ascaris lumbricoides for the study of the effect of drugs in vitro is described.2. Stimulant drugs which are classified as nicotine-like in mammalian pharmacology increased the isometric tension of this preparation. These drugs were, in descending order of potency: dimethylphenylpiperazinium, nicotine, acetylcholine, carbachol, decamethonium and pyridine-2-aldoxime methiodide.3. Muscarine-like drugs (oxotremorine, methacholine, pilocarpine) had no activity.4. Potassium and barium ions stimulated the tissue, while the anti-cholinesterases, dichlorvos and eserine, increased the resting tension of the preparation and potentiated the responses to acetylcholine.5. Adrenaline neither stimulated the tissue nor affected the responses to nicotine-like drugs.6. The relative potency of several blocking agents which antagonize the responses to nicotine-like drugs was assayed. These blocking agents were, in descending order of potency: mecamylamine, (+)-tubocurarine, hexamethonium, atropine and piperazine. Acetylcholine, dimethylphenylpiperazinium and pyridine-2-aldoxime methiodide apparently act on a common receptor, for each blocking agent had a similar molar inhibitory concentration against these stimulants.7. It is concluded that the cholinoceptor in muscle preparations of Ascaris lumbricoides is pharmacologically similar to that of the mammalian autonomic ganglion.

Acetylcholine↗
PubMed1969

Hydrolysis of suxamethonium by different types of plasma.

1. A method, based on the use of the isolated frog rectus abdominis preparation, is described for studying quantitatively the hydrolysis of suxamethonium at low concentrations.2. Rates of hydrolysis of butyrylcholine, 10 mM, benzoylcholine, 0.05 mM, and suxamethonium, 0.025 mM, by plasma from different species and human plasma with genetic variants of cholinesterase were measured.3. The rates of hydrolysis of suxamethonium by different types of plasma vary widely. Human plasma with usual cholinesterase and monkey plasma hydrolyse suxamethonium more speedily than do the plasma of cats, dogs and rats, and human plasma with either atypical or fluoride resistant cholinesterase. This is only to a small extent attributable to differences in enzyme concentration and not explained by the presence of an inhibitor.4. The K(m) values for butyrylcholine are very similar for different types of plasma but the K(I) values for suxamethonium in the system plasma-butyrylcholine-suxamethonium vary greatly.5. These results and observations on the inhibition by decamethonium of the hydrolysis of butyrylcholine are consistent with the interpretation that the rates of hydrolysis of suxamethonium, 0.025 mM, obtained with different types of plasma vary because they are a function of two variables, the affinity of the ester for cholinesterase and the stability of the monosuccinyl derivative of the cholinesterase. It seems that human plasma with atypical cholinesterase hydrolyses suxamethonium much slower than does human plasma with usual cholinesterase mainly or solely because of differences in affinity of the ester for the two enzymes. On the other hand, cat plasma appears to hydrolyse suxamethonium much slower than does human plasma with usual cholinesterase mainly because the monosuccinyl derivative of cholinesterase in cat plasma is much more stable than that in human plasma. The reverse might apply for monkey plasma.6. Inhibition by dibucaine or sodium fluoride of the hydrolysis of benzoylcholine is not a general guide to rates of hydrolysis of suxamethonium by different types of plasma.

Animals↗
PubMed1970

Aspects of the pharmacology of a new anthelmintic: pyrantel.

1. The pharmacological properties of an anthelmintic, pyrantel, and some of its analogues have been described and compared with piperazine in a variety of vertebrate and helminth preparations.2. Pyrantel and its analogues in common with nicotine and decamethonium cause spastic paralysis in chicks and contracture of the chick semispinalis and toad rectus abdominis muscles.3. In the soleus and anterior tibialis muscles of the cat, pyrantel in large amounts caused a short-lived neuromuscular block that was preceded by initial depolarization.4. In preparations from cat and rat, pyrantel showed properties common to both competitive and depolarizing neuromuscular blocking drugs.5. Pyrantel blocked the contracture evoked by transmural stimulation and caused a marked contracture of the worm. Piperazine caused a gradually developing reduction in the responses to transmural stimulation and no contracture.6. Pyrantel and its analogues caused a slowly developing contracture of strip preparations of Ascaris, being more than 100 times more active than acetylcholine in this respect. Piperazine caused a relaxation of Ascaris strip preparations and in common with (+)-tubocurarine blocked the responses to acetylcholine and pyrantel analogues on this preparation.7. Pyrantel caused depolarization and increased spike discharge frequency in single muscle cells of Ascaris, these changes being accompanied by increase in tension. Piperazine, on the other hand, caused hyperpolarization and reduction in spike discharge frequency and relaxation, and antagonized the effects of pyrantel.

Animals↗
PubMed1971

Effect of eserine on the chick biventer cervicis preparation.

1. The relationship between the capacity of the chick biventer preparation, both intact tissue and homogenate, to inactivate acetylcholine and the ability of eserine to increase the sensitivity of the tissue to acetylcholine have been investigated.2. At concentrations of eserine of 2.69 x 10(-9)M and 2.69 x 10(-8)M the capacity of the whole tissue to inactivate acetylcholine is reduced by 5% and 15% respectively. These concentrations of eserine increase the sensitivity of the preparation to acetylcholine by factors of 2 and 4 respectively, without a change of slope in regression lines.3. At concentrations of eserine of 2.69 x 10(-7)M and 2.69 x 10(-6)M the capacity of the whole tissue to inactivate acetylcholine is reduced by 40% and 80% respectively, and the sensitivity to acetylcholine increased by factors of 70 and 800 respectively, along with marked increases in the slopes of the regression lines.4. An attempt has been made to quantify these differences by proposing a model in which cholinesterase in the tissue is regarded as a network, preventing the access of a large fraction of the acetylcholine to its site of action.5. It is suggested that, whereas the increase in sensitivity to acetylcholine at eserine concentrations of 2.69 x 10(-9)M and 2.69 x 10(-8)M can be interpreted as an anticholinesterase effect (which is still present at higher concentrations), that seen at the higher concentrations may represent a direct action of eserine on the tissue.6. It is further suggested that there are barriers to penetration in intact tissue to both substrate and inhibitor, which invalidate attempts to extrapolate results from homogenates.

Acetylcholine↗
PubMed1971

Diffusion of labelled substances through isolated rat diaphragm.

1. The rate of diffusion of [(14)C] sucrose through rat diaphragm muscle is dependent on the period of preliminary soaking of the muscle in Krebs solution at 36 degrees C. The ratio of the length of the diffusion path through the diaphragm to its geometrical thickness appears to fall from 4.39+/-0.38 (S.E. of the mean) to 2.23+/-0.18 after about 6 h of soaking.2. The area of the diaphragms available for diffusion is apparently constant at 0.3-0.4 of their total area.3. The measured thickness of the diaphragms increases by about 20% on soaking.4. Entry of [(131)I] iodide into the muscle fibres is detected as a fall in both steady state and non-steady state rates of diffusion through the diaphragm.5. Entry of [(14)C-methyl] decamethonium into the muscle cells is not evident from such diffusion studies in normal Krebs solution.

Animals↗
PubMed1974

The properties of muscarinic receptors in mammalian cerebral cortex.

1 The reaction of tritiated propylbenzilylcholine mustard ([(3)H]-PrBCM; N-2'-chloroethyl-N-[2'',3''-(3)H(2)] -propyl-2-aminoethylbenzilate) with homogenates of mammalian brain has been studied.2 The uptake can be divided into an atropine-sensitive component of fixed capacity (380 pmol/g protein in the rat) and an atropine-insensitive part.3 The atropine-sensitive portion is identified as muscarinic receptor by its insensitivity to nicotinic antagonists and anticholinesterases and its sensitivity to a range of muscarinic antagonists.4 The uptake of [(3)H]-PrBCM is also inhibited by muscarinic agonists and there is reasonable quantitative agreement between the affinities of agonists estimated in this way and in intact tissues by physiological responses.5 The fraction of [(3)H]-PrBCM uptake inhibited by muscarinic antagonists and agonists is the same.6 The amount of receptor found in six mammalian species was inversely related to the size of the brain, but the rates of alkylation and the sensitivity to atropine were not dissimilar.

Animals↗
PubMed1975

Decamethonium in the perfused and immersed rat diaphragm.

1 The water content and mannitol space of rat diaphragms which were perfused through the inferior vena cava was increased compared with immersed diaphragms. The potassium content of both preparations, when expressed in terms of dry weight, was maintained at similar values to that found in vivo. 2 Despite the application of a constant concentration of decamethonium, a steady level of neuromuscular block was not obtained in either the perfused or immersed rat diaphragm. The immersed preparation differed from the perfused preparation in that recovery from paralysis occurred despite the continued presence of the drug. 3 The rate of uptake of labelled decamethonium (100 muM) at the end-plate region was similar in the perfused and immersed diaphragm. The slopes of the regressions were 0.059 and 0.054 mul mg-1 min-1 (based on dry weight) respectively which were not significantly different. This implies that the rate of uptake of the drug at the end-plate is slow and limited by the rate of entry into the fibre rather than by diffusion to the site of entry.

Animals↗
PubMed1976

A comparison of the time course of excitation and inhibition by iontophoretic decamethonium in frog endplate.

1 The depolarization of frog endplate by a brief iontophoretic application of decamethonium was slower in time course than the inhibition of a long carbachol response produced by the same decamethonium pulse, or than the excitation produced by a brief equipotent carbachol pulse. 2 The delay between the peak inhibition and peak excitation produced by decamethonium, about 50 ms, is too great to be explained by slow receptor activation kinetics, since Katz & Miledi (1973) have shown that the lifetime of decamethonium-activated receptors is only 0.25 milliseconds. 3 If doses of carbachol and decamethonium are adjusted to give response amplitudes in the ratio corresponding to the ratio of their presumed maximum responses, then there is little difference in the time courses of the responses. 4 This observation, together with the finding that increasing the dose applied slows the decamethonium response much more than the carbachol response, suggests that a decamethonium response contains contributions from a much wider area of receptive membrane than does a carbachol response of equal amplitude. 5 Simulation shows that these geometrical effects are sufficient to account for the rapidity of inhibition compared to excitation without postulating slow receptor kinetics. 6 It is pointed out that similar effects may account for certain results obtained in iontophoretic studies of desensitization.

Animals↗