Muscle preparation

Although in in vivo circumstances an intracellular free calcium increase apparently acts as the primary modulator of contraction, it can be bypassed in highly permeabilized smooth muscle preparations where the active subunit of MLCK can be introduced to phosphorylate myosin and induce contraction. The MLCK catalyzed phosphorylation of serine-19 is seen as the necessary event in the activation of smooth muscle myosin to form crossbridges. Thus, the rising phase of force during an isometric smooth muscle contraction follows an increase in the degree of phosphorylation of myosin, and that in turn follows the transient rise of (a) cytosolic free Ca, (b) Ca-calmodulin complexes, and (c) the active form of MLCK. The regulation of the intracellular calcium is discussed below. The dynam-... 

However, the total regulatory system is not so simple and linear. In skinned muscle preparations especially, it can be shown that there are calcium stores which cannot be released by IP3 but which are released by elevated levels of calcium itself That is, by the mechanism of calcium induced calcium release (CICR). The CICR... 

This section examined small muscle preparations stimulated electrically or skinned muscle fibers maintained in superfused baths with different substance concentrations. The electrical stimulation was either continuous or intermittent for relatively short durations. 

When a nerve-muscle preparation is stimulated in the presence of a sea snake neurotoxin, there is no twitch. However, when the muscle itself is stimulated directly in the presence of a neurotoxin, the muscle contracts. This means that neurotoxin does not inhibit the muscle itself. Moreover, postsynaptic neurotoxin does not inhibit the release of acetylcholine from the nerve ending. Therefore, the site of snake toxin inhibition must be in the postsynaptic site 20). Later it was shown that a neurotoxin strongly binds to the acetylcholine receptor (AChR). 

Until the recent development of appropriate HPLC techniques capable of detecting pmol amounts (see Flentge et al. 1997) ACh could only be measured chemically by relatively lengthy and expensive procedures (e.g. gas chromotography), which were not always very sensitive, or by bioassays. Although the latter, using muscle preparations that responded to ACh, such as the dorsal muscle of the leech, the rectus abdominus of the frog or certain clam hearts, were reasonably sensitive they were tiresome and not easily mastered. Thus studies on the release and turnover of ACh have not been as easy as for the monoamines. 

AMOS s, OKWUASABA F K, GAMANIEL K, AKAH P, WAMBEBE c (1998) Inhibitory effects of the aqueous extract of Pavetta crassipes leaves on gastrointestinal and uterine smooth muscle preparations isolated from rabbits, guinea pigs and rats. J Ethnopharmacol. 61 209-13. 

Ruigt, G.S.F. and J.V.D. Bercken. 1986. Action of pyrethroids on a nerve-muscle preparation of the clawed frog, Xenopus laevis. Pestic. Biochem. Physiol. 25 176-187. 

Somlyo It is possible in smooth muscle preparations to do high frequency stimulation of nerves, and get a contraction that is abolished by TTX. This suggests that the transmitter does get to the smooth muscles. This is a physiological experiment. 

Wray Can we take the discussion one step back We have heard about the horrors of cultured cells, and the difficulty of doing anything in intact tissue. Ted Burdyga, you have comparisons of single cells and intact bundles. How robust a model are single cells for the intact muscle preparations ... 

N, O-Diacylated or O-alkylated N-hydroxysulfonamides release nitroxyl (HNO) upon hydrolysis or metabolic dealkylation, as determined by gas chromatographic identification of nitrous oxide in the reaction headspace [27-29, 38]. Scheme 7.5 depicts the decomposition of a representative compound (7) to a C-acyl nitroso species that hydrolyzes to yield HNO. Either hydrolysis or metabolism removes the O-acyl or O-alkyl group to give an N-hydroxy species that rapidly decomposes to give a sulfinic acid and an acyl nitroso species. This C-acyl nitroso species (8) hydrolyzes to the carboxylic acid and HNO (Scheme 7.5). These compounds demonstrate the ability to relax smooth muscle preparations in vitro and also inhibit aldehyde dehydrogenase, similar to other HNO donors [27, 29]. 

The cholinesterase-inhibiting activity of the phosphorofluoridates was compared quantitatively with that of eserine sulphate thus. To 0-2 ml. of heparinized human plasma was added 05 ml. of a solution containing either eserine or the phosphorofluoridate in varying concentrations then the mixture was kept at room temperature for 10 min. before 1 /tg. of acetylcholine in 1 c.c. saline solution was added. After 5 min. at room temperature, the mixture was made up to 10 ml. with frog saline containing eserine 1/100,000, which at once stopped the action of any cholinesterase not yet inactivated. The solution was then assayed for acetylcholine on the frog rectus-muscle preparation. 

With the exception of Buchner s yeast extract and some comparable muscle preparations (Chapter 4), disrupting tissues often caused such damage to cells that normal metabolism was irreversibly affected. A further obstacle was that classical methods of analysis were neither sufficiently sensitive, rapid nor simple enough for the multiple measurements required to follow chemical changes in small samples of tissue. 

In the next 2 to 3 years further experiments, particularly by Eggleston, who had joined Krebs in January 1936, confirmed and extended the observations. Careful quantitative evaluation of the data indicated that citrate like fumarate (Szent-Gyorgi) and like ornithine in the urea cycle exerted a catalytic effect on muscle metabolism. If arsenite, which blocks 2-oxoglutarate oxidation, was added with citrate to a respiring pigeon-muscle preparation, 2-oxoglutarate accumulated. 

Stucker 0, Pons C, Duverger JP, Drieu K. (1996). Effects of Ginkgo biloba extract (EGb 761) on arteriolar spasm in a rat cremaster muscle preparation. Int J Microcirc Clin Exp. 16(2) 98-104. Subhan Z, Flindmarch I. (1984). The psychopharmacological effects of Ginkgo bilote extract in normal healthy volunteers. Int J Clin Pharmacol Res. 4(2) 89-93. 

In Vitro Mediator Release. Although no pulmonary effects have been demonstrable in guinea pigs following inhalation of bract extract (104), contraction of isolated guinea pig ileum by extracts (105,106) has been reported. Aqueous extracts of cotton, jute, flax, and hemp cause contractions of isolated guinea pig ileirni or tracheal muscle preparations which are similar in time of onset and duration to those produced by... 

Delayed constrictor responses in guinea pig smooth muscle preparations following challenge with jute extract have been observed. The response diminishes with successive doses of extract as though some "store" is being depleted, until, finally, constriction is not seen. Cotton extract is a more potent contracting agent than jute. 

Currently, all five toxic components from concavum are being subjected to column and high performance liquid chromatography. Products of these treatments will be evaluated and characterized using the mouse bioassay and isolated nerve-muscle preparations. 

Reports of effects on mice observed for maitotoxin closely resemble the effects of ciguatoxin, with the exception of diarrhea, hypersalivation, and convulsions before death. The symptoms observed here for ESAP did not include hypersalivation and only occasionally was mild diarrhea observed. The vasodilation in the ears, ptosis of the eyelids and abdomen were observed in this study but not in other accounts. Crude extracts produced irreversible inhibition of the frog nerve muscle preparation, affecting first the synapse, secondly the nerve and lastly the muscle (23). At. 04 mg/ml the crude extract completely inhibited the isolated guinea pig ileum preparation. 

The most recent reports on the action of the water soluble toxin from G, toxicus concluded that this toxin, referred to as maitotoxin, invokes an unmediated stimulatory (contractile) response on contact with guinea pig ileal smooth muscle preparations. Furthermore, this response was said to be due to an activation of calcium channels in the smooth muscle membranes (J7). Previous studies of this toxin from the same source indicated that it produces an inhibitory effect on guinea pig atrial muscle (28, 19). 

The present study reports on the effects of the water soluble toxin from toxicus from the Caribbean on guinea pig ileal smooth muscle preparations. It also compares the results obtained from the water soluble toxin with those obtained using lipid extraction. 

Pharmacology In isolated nerve-muscle preparation, dantrolene produced relaxation by affecting contractile response of the skeletal muscle at a site beyond the myoneural junction and directly on the muscle itself. In skeletal muscle, the drug dissociates the excitation-contraction coupling, probably by interfering with the release of calcium from the sarcoplasmic reticulum. 

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