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At least 343 records · Page 19Linked to original sources
PubMed1977

Binding of alpha-bungarotoxin and cholinergic ligands to acetylcholine receptors in the membrane of skeletal muscle.

A membrane fraction enriched in acetylcholine receptors was prepared from denervated cat leg muscles. 97% of the alpha-bungarotoxin-binding sites in the dispersed membranes are sensitive to nicotinic cholinergic ligands. In intact msucle, 90% are. A filtration assay of the binding to the membranes of tritiated alpha-bungarotoxin, as retarded by these ligands, provides a convenient system for the determination of affinities of ligands for the muscle receptor in its membrane-bound state. Affinities were found thus for 6 nicotinic ligands. An allosteric system, rather than desensitisation, may explain the high affinities observed for certain ligands.

Acetylcholine↗
PubMed1985

Acetylcholine and carnitine sensitive growth in a Drosophila cell line.

Growth yield in cultures of Schneider's line 2 cells was studied as a function of plating cell density. It was measured in the presence of various neurotransmitters, hormones and related chemicals. Of these, acetylcholine and carnitine were studied in detail. Both significantly increased growth yields at low plating cell densities. Atropine and tubocurarine significantly reduced growth yield, suggesting the presence of a cholinergic-like receptor. Cell populations were incubated with [14C]choline and uptake occurred. The [14C]choline was incorporated into the production of secreted molecules which comigrated with carnitine offering evidence for carnitine production and secretion.

Acetylcholine↗
PubMed1992

Possible role during exocytosis of a Ca(2+)-activated channel in neurohypophysial granules.

Ion channels from bovine neurohypophysial granules were incorporated into artificial lipid bilayers. The larger amplitude channel is permeable to cations and exhibits multiple conductances. The channel opens only in the presence of free Ca2+, but is inhibited by relatively high Ca2+ concentrations. Release of vasopressin from permeabilized neurohypophysial terminals also shows a similar biphasic dependence on Ca2+. Release is selectively inhibited by low concentrations of the long-chain alcohol octanol, but not by high concentrations of ethanol, as is the neurosecretory granule Ca(2+)-activated cation channel. Furthermore, Ca(2+)-evoked release and channel activity are both inhibited by the long-chain tetraethylammonium analogs decamethonium and decyl-triethyl ammonium bromide. The close correlation between channel and release properties lead us to conclude that the Ca(2+)-activated channel is involved in peptide secretion.

Alcohols↗
PubMed2005

The theaflavin fraction is responsible for the facilitatory effect of black tea at the skeletal myoneural junction.

The effect of various fractions of black tea [(Camellia Sinensis) (L) O. Kuntze (Theaceae)] on the function of mammalian skeletomotor apparatus was studied. The theaflavin fraction (Tfs) produced a concentration- dependent facilitation of indirect twitch responses of the rat phrenic nerve diaphragm preparation and the facilitation was dependent on the amount of calcium present in the bathing fluid. Nifedipine reduced the facilitatory effect of Tfs as a function of its concentration. Tfs failed to produce facilitation when the twitch height was reduced to about 50% of the control value in presence of magnesium chloride. Tfs completely antagonized the submaximal paralytic effect of d- tubocurarine and decamethonium bromide. Tfs did not have any effect on direct twitch responses or on acetylcholine (Ach) and potassium chloride (KCl) induced contractures of denervated diaphragm. The results revealed that the site of action of Tfs is on the contractile mechanism of the voluntary muscle and point to a critical role of calcium in the mechanism of action of Tfs. N omega-nitro-L-arginine-methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, antagonized both the facilitatory and inhibitory effects on indirect twitch responses of rat diaphragm induced by L-arginine and Tfs when the phrenic nerve was stimulated at 5 Hz and 50 Hz respectively. The thearubigin (Trs) fraction of black tea and the aqueous part which is completely devoid of Tfs, did not potentiate the twitch responses. The findings suggest that Tfs have a potentiating effect on the contractile mechanism of skeletal muscle and that calcium and nitric oxide may modulate this action of Tfs.

Animals↗
PubMed1983

Succinyldicholine and the basic ocular deviation.

We measured the ocular positions of conscious and anesthetized subjects from photographs. We obtained the conscious basic horizontal deviation by using the cover-uncover test. Intravenously administered succinyldicholine chloride, 2 mg/kg of body weight, returned the eyes of 15 anesthetized volunteers to positions that agreed well with those of their conscious horizontal basic deviations in the primary position. The mean ratio (+/- S.E.) calculated by dividing the horizontal interlimbal distance 90 seconds after drug injection by that of the same subject's horizontal interlimbal conscious basic deviation was 0.99 +/- 0.01. This result supported the theory that the multiply innervated (en grappe) extraocular muscle fibers were responsible for the basic deviation. Macaca nemestrina monkeys and baboons proved to be unsuitable primate models for the human succinyldicholine response. In humans, the drug-induced ocular position was often vertically above or below the primary position. The associated horizontal deviation appeared to follow the physiologic V pattern, being more divergent if the eyes were rotated up and more convergent if the eyes were rotated down. In one third of the subjects this vertical deviation resulted in drug-induced horizontal interlimbal distances that disagreed by more than 5% with those of the conscious basic deviation in the primary position. This effect makes succinyldicholine of little value for making quantitative estimates of the amount of ocular muscle surgery to be performed during strabismus correction procedures. We injected succinyldicholine at the conclusion of strabismus surgery in eight subjects to determine if the drug-induced ocular positions would predict the postoperative results. The muscles operated on responded as though temporarily paretic. The drug-induced ocular positions bore no resemblance to the postoperative results.

Adult↗
PubMed1985

Potassium efflux from single skinned skeletal muscle fibers.

The efflux of 42K from single, skinned (sarcolemma removed) skeletal muscle fibers has been determined. Isotope washout curves are kinetically complex and can be fit as the sum of three exponentials, including a fast component (k = 0.25 s-1) with a pool size equivalent to 91% of the fiber volume, an intermediate component (k = 0.08 s-1) equivalent to 6% of the fiber volume, and a slow component (k = 0.008 s-1) equivalent to 0.5% of fiber volume. Only the intermediate kinetic component is significantly affected by pretreatment of fibers with detergent. Efflux curves from detergent-treated fibers could be fit as the sum of two exponentials with coefficients and rate constants comparable to those of the fast and slow component of washout of untreated controls. Similarly the washout of [14C]sucrose can be described as the sum of two exponentials. We conclude that the intermediate component of 42K washout results from the movement of ions from a membrane bound space within the skinned fiber. Because of its relative volume, the sarcoplasmic reticulum seems to be a reasonable choice as a structural correlate for this component. Our estimate of the potassium permeability for the sarcoplasmic reticulum (SR) based on the efflux data is 10(-7) cm/s. This value is less than previous estimates from isolated preparations.

Animals↗
PubMed1997

The cytosolic inactivation domains of BKi channels in rat chromaffin cells do not behave like simple, open-channel blockers.

Most BK-type voltage- and Ca(2+)-dependent K+ channels in rat chromaffin cells exhibit rapid inactivation. This inactivation is abolished by brief trypsin application to the cytosolic face of membrane patches. Here we examine the effects of cytosolic channel blockade and pore occupancy on this inactivation process, using inside-out patches and whole-cell recordings. Occupancy of a superficial pore-blocking site by cytosolic quaternary blockers does not slow inactivation. Occupancy of a deeper pore-blocking site by cytosolic application of Cs+ is also without effect on the onset of inactivation. Although the rate of inactivation is relatively unaffected by changes in extracellular K+, the rate of recovery from inactivation (at -80 and -140 mV with 10 microM Ca2+) is faster with increases in extracellular K+ but is unaffected by the impermeant ion, Na+. When tail currents are compared after repolarization, either while channels are open or after inactivation, no channel reopening is detectable during recovery from inactivation. BK inactivation appears to be mechanistically distinct from that of other inactivating voltage-dependent channels. Although involving a trypsin-sensitive cytosolic structure, the block to permeation does not appear to occur directly at the cytosolic mouth or inner half of the ion permeation pathway.

Adrenal Medulla↗
PubMed1998

Nuclear clustering in myotubes: a proposed role in acetylcholine receptor mRNA expression.

We investigated the functional relationship between nuclear topology, as expressed by degree and type of nuclear aggregation, and appearance of acetylcholine receptor (AChR) subunit mRNAs. Embryonic chick muscle cell cultures treated with the muscle activity blocking agents decamethonium (DCM), d-tubocurare (TBC), and tetrodotoxin (TTX) or co-cultured with cholinergic neurons were examined for the influence of muscle activity on nuclear aggregation and its effects on AChR alpha-, gamma-, and delta-subunit message expression. mRNA was measured by in situ hybridization and nuclei were visualized by bis-benzimide DNA staining. DCM and TBC treatments, as well as neuronal co-culture, resulted in increased nuclear clustering within myotubes and a per nucleus upregulation in mRNA expression relative to control for each subunit. The pattern of nuclear aggregation was treatment dependent, with more and larger aggregates found when myotubes were co-cultured with neurons. Moreover, as nuclear aggregates became larger: (1) nearly all nuclei within active aggregates expressed mRNA and (2) local accumulation (mRNA per unit area) was elevated relative to single nuclei, while per nucleus mRNA production decreased. To determine whether mRNA expression was transient and did not result in steady-state upregulation of AChR receptor protein, we performed a double labeling of surface AChRs with 125I-alpha-bungarotoxin (125I-alpha-BTX) concomitant to the in situ hybridization for mRNA quantification on TTX treated muscle cells. Surface receptor expression tracked mRNA expression forall types of nuclear topology observed, indicating that message levels are in fact reliable indicators of receptor population on the plasma membrane surface in myotubes. We propose that nuclear clustering is an organelle-level, accessory mechanism whereby cells concentrate relatively large amounts of AChR mRNA/protein in specific myotube regions.

Animals↗
PubMed1977

Allosteric interactions between the membrane-bound acetylcholine receptor and chemical mediators: equilibrium measurements.

An approach to equilibrium dialysis measurements has been developed which enables one to study the interaction of chemical mediators with the membrane-bound acetylcholine receptor and to gain information of a type previously obtainable only with soluble proteins. Equilibrium dialysis experiments conducted at pH 7.0,4 degrees C, and mu = 0.18 M, with electroplax membrane preparations from Electrophorus electricus revealed apparently homogeneous binding isotherms for decamethonium with dissociation constants in the range of 0.2-0.4 muM. The following new information has been obtained. (1) The activators of neural transmission, decamethonium and carbamylcholine, occupy overlapping binding sites. (2) These activators and the inhibitors, alpha-bungarotoxin and d-tubocurarine, compete for only one-half of the sites available to them even through the stoichiometry of these is 1:1 as measured with decamethonium (a reversibly binding activator) and alpha-bungarotoxin (an irreversible specific inhibitor). Different receptor molecules, preexisting nonequivalent binding sites, or an allosteric mechanism involving ligand-induced conformational changes are often considered to account for such observations.

Acetylcholine↗