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S H Bryant

Publications and source records attributed to S H Bryant.

At least 55 records · Page 3Linked to original sources
PubMed1991

Modulation of rat skeletal muscle chloride channels by activators and inhibitors of protein kinase C.

The membrane electrical parameters and component conductances of rat extensor digitorum longus muscle fibres were studied in vitro at 30 degrees C with standard two microelectrode square pulse cable analysis in the presence of protein kinase C (PKC) activators and inhibitors. The PKC activator, 4-beta-phorbol-12,13 dibutyrate (4-beta-PDB), (2-90 nM) blocked up to 67% chloride conductance (GCl) in rat skeletal muscle fibres and induced myotonic hyperexcitability. The concentration necessary to produce a 50% block of the membrane GCl was 23 nM. The "inactive" 4-alpha-phorbol-12,13 dibutyrate had no effect at 2 microM. The blocking effect of 4-beta-PDB on GCl was prevented by preincubation of the preparations with the PKC inhibitors, staurosporine (1-5 microM) and tetrahydropapaverolone (50-100 microM). The blocking effects on membrane GCl of 4-beta-PDB and its antagonism by the inhibitors used support the concept of the involvement of PKC in regulating Cl channels of mammalian skeletal muscle fibres.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1990

Optical evidence for a chloride conductance in the T-system of frog skeletal muscle.

T-system action potentials were recorded optically from intact frog skeletal muscle fibers stained with the non-penetrating potentiometric dye NK-2367. The effect of chloride removal on the falling phase of the radially propagating tubular action potential was studied to determine whether a chloride conductance located in the T-system membranes contributes to tubular repolarization during activity. Our results show that, in chloride-free Ringer, repolarization of the tubular action potential is significantly slowed. Moreover, the late phase of tubular repolarization is characterized by a large after-potential, which is highly temperature-dependent and appears as a secondary peak above 10 degrees C. The optical data were compared with predicted T-system action potentials generated from a radial cable equivalent circuit model of the T-system, in which the effects of a distributed tubular leak conductance were tested. Results of this analysis are consistent with the proposal that some of the outward repolarization current during the T-system action potential is drawn across a chloride conductance located in the T-system membranes.

Action Potentials↗
PubMed1990

Enantiomeric effects on excitation-contraction coupling in frog skeletal muscle by a chiral phenoxy carboxylic acid.

Aromatic monocarboxylic acids are known to significantly potentiate the mechanical response of skeletal muscle fibers. In this study we investigated the effects of enantiomers of 2-(4-chlorophenoxy)propionic acid, chemically one of the simplest aromatic monocarboxylic acids with chiral properties, on mechanical threshold and charge movement in frog skeletal muscle. The R(+), but not the S(-), enantiomer lowered rheobase mechanical threshold and shifted charge movement to more negative potentials. The R(+) enantiomer also significantly slowed charge movement kinetics, with pronounced delays of the OFF charge transitions. These effects required high temperature for their production. The stereospecific actions of the R(+) enantiomer are interpreted in terms of a specific interaction of this compound at an anion-sensitive site involved in excitation-contraction coupling, most likely on the dihydropryidine-sensitive voltage sensor in the T-system.

2-Methyl-4-chlorophenoxyacetic Acid↗
PubMed1989

The effects of taurine on pharmacologically induced myotonia.

Taurine reduces the excitability of striated muscle fibers by increasing the membrane conductance to chloride ions (GCl). This action was tested on rats made myotonic by drugs that block GCl by different mechanisms. Experiments were made "in vivo" using electromyographic (EMG) recordings and "in vitro" with intracellular microelectrode recordings from extensor digitorum longus muscle fibers. Taurine did not antagonize the myotonic discharges produced in vivo by anthracene-9-carboxylic acid, nor did it restore GCl lowered in vitro by this agent. However, when myotonia was chronically induced by 20,25 diazacholesterol, taurine given chronically in vivo or acutely in vitro antagonized the EMG myotonia as well as the reduced GCl and increased excitability of single fibers. We conclude that taurine acts directly on chloride channels to modify their kinetics. Our findings suggest that further clinical studies on the use of taurine in muscle disease involving abnormal excitability or chloride channel function will be useful.

Animals↗
PubMed1989

PKB: a program system and data base for analysis of protein structure.

PKB is a computer program system that combines a data base of three-dimensional protein structures with a series of algorithms for pattern recognition, data analysis, and graphics. By typing relatively simple commands the user may search the data base for instances of a structural motif and analyze in detail the set of individual structures that are found. The application of PKB to the study of protein folding is illustrated in three examples. The first analysis compares the conformations observed for a short sequential motif, sequences similar to the cell-attachment signal Arg-Gly-Asp. The second compares sequences observed for a conformational motif, a 16-residue beta alpha beta unit. The third analysis considers a population of substructures containing ion-pair interactions, examining the relationship of frequency of occurrence to calculated electrostatic energy.

Amino Acid Sequence↗
PubMed1989

The surface area of monomeric proteins: significance of power law behavior.

The coefficients in a power law fit of accessible area versus molecular weight for high-resolution monomeric protein structures are assessed with respect to statistical accuracy using bootstrap analyses, and with respect to physical significance using model systems and the concept of roughness or fractal structure of the protein surface.

Models, Statistical↗
PubMed1988

Enantiomers of clofibric acid analogs have opposite actions on rat skeletal muscle chloride channels.

The S-(-) isomers of a series of clofibric acid analogs produced only a block of chloride conductance of rat skeletal muscle fibers with increasing concentrations until block was nearly complete. The R-(+) isomers, on the other hand, at low concentrations increased chloride conductance by as much as 9% to 39% and at higher concentrations decreased chloride conductance, but never by more than 27% of the control value. The actions of the enantiomeric pairs to either produce or inhibit myotonic excitability paralleled their ability to block or increase chloride conductance, respectively.

Animals↗
PubMed1988

Action of diltiazem on excitation-contraction coupling in bullfrog skeletal muscle fibers.

In this study the calcium antagonist drug diltiazem was found to produce twitch potentiation, lower the mechanical threshold potential and block inward calcium currents in bullfrog skeletal muscle fibers. Under tonic conditions (stimulation either every 1 or 2 min) high concentrations of diltiazem were required to enhance twitch tension (ED50 = 249 microM) and block calcium currents (IC50 = 190 microM). In addition, 100 microM diltiazem lowered the mechanical threshold rheobase potential from -49.3 to -57.0 mV. At higher rates of stimulation, concentrations of diltiazem as low as 1 and 10 microM, which had no tonic action, were found to produce twitch potentiation and calcium channel block, respectively. Onset and washout of tonic and frequency-dependent actions of diltiazem on twitch and current amplitude occurred over a similar time course. It is proposed that the mechanical potentiation, as well as the calcium channel block produced by diltiazem, result from the interaction of diltiazem with the same or similar receptor site(s).

Animals↗
PubMed1987

Kinetic basis for insensitivity to tetrodotoxin and saxitoxin in sodium channels of canine heart and denervated rat skeletal muscle.

The single-channel blocking kinetics of tetrodotoxin (TTX), saxitoxin (STX), and several STX derivatives were measured for various Na-channel subtypes incorporated into planar lipid bilayers in the presence of batrachotoxin. The subtypes studied include Na channels from rat skeletal muscle and rat brain, which have high affinity for TTX/STX, and Na channels from denervated rat skeletal muscle and canine heart, which have about 20-60-fold lower affinity for these toxins at 22 degrees C. The equilibrium dissociation constant of toxin binding is an exponential function of voltage (e-fold per 40 mV) in the range of -60 to +60 mV. This voltage dependence is similar for all channel subtypes and toxins, indicating that this property is a conserved feature of channel function for batrachotoxin-activated channels. The decrease in binding affinity for TTX and STX in low-affinity subtypes is due to a 3-9-fold decrease in the association rate constant and a 4-8-fold increase in the dissociation rate constant. For a series of STX derivatives, the association rate constant for toxin binding is approximately an exponential function of net toxin charge in membranes of neutral lipids, implying that there is a negative surface potential due to fixed negative charges in the vicinity of the toxin receptor. The magnitude of this surface potential (-35 to -43 mV at 0.2 M NaCl) is similar for both high- and low-affinity subtypes, suggesting that the lower association rate of toxin binding to toxin-insensitive subtypes is not due to decreased surface charge but rather to a slower protein conformational step. The increased rates of toxin dissociation from insensitive subtypes can be attributed to the loss of a few specific bonding interactions in the binding site such as loss of a hydrogen bond with the N-1 hydroxyl group of neosaxitoxin, which contributes about 1 kcal/mol of intrinsic binding energy.

Animals↗
PubMed1987

Suppression of charge movement by calcium antagonists is not related to calcium channel block.

The calcium channel-inhibiting drugs nitrendipine and diltiazem represent two important classes of organic calcium antagonists. In the present study, the effect of these drugs on calcium currents and charge displacement currents in bullfrog semitendinosus muscle fibers was examined using a vaseline gap voltage clamp. Nitrendipine (10 microM) reduced the quantity of charge that moved both during the ON phase (QON) and the OFF phase (QOFF) of charge movement. This action appeared to be most selective for QON. However, at this same concentration, nitrendipine had no blocking action on inward calcium currents. In contrast to these findings, diltiazem blocked calcium currents in a concentration-dependent manner, while slightly increasing the quantity of charge moved during QON and QOFF. The enhancement of charge movement by diltiazem resulted from two actions. First, diltiazem shifted the voltage-dependence of charge movement to more negative potentials. Second, diltiazem increased the maximum amount of charge moved.

Animals↗
PubMed1987

The action of taurine on chloride conductance and excitability characteristics of rat striated muscle fibers.

Taurine and related compounds were applied to rat extensor digitorum longus muscle fibers in vitro, and the effects on membrane potential, cable parameters, component conductances and excitability were observed with microelectrodes. After 20 min in 60 mM taurine the fibers hyperpolarized and there were decreases in the latency of a rheobasic stimulus, the duration of the action potential and the maximum number of spikes elicited by depolarizing pulses. The effects of taurine on membrane resistance are attributed to a specific dose-dependent increase in membrane chloride conductance (G) with little or no effect on membrane potassium conductance. C1Gamma-aminobutyric acid at 30-60 mM also produced a specific increase in GC1 but, unlike taurine it caused a significant depolarization. beta-alanine or sucrose at 60 mM did not mimic any of the effects observed with taurine at this concentration. It was concluded that the actions of taurine and GABA on excitability can be explained by increases in GC1.

Alanine↗
PubMed1987

Dissociation of hypolipidemic and antiplatelet actions from adverse myotonic effects of clofibric acid related enantiomers.

Enantiostructure-activity studies of chlorophenoxybutyric and propionic acids have provided evidence for the dissociation of serum cholesterol lowering and platelet antiaggregatory activities from the adverse chloride ion channel mediated myotonic effects of these compounds. R-(+) propionic and butyric acid enantiomers, unlike achiral clofibric acid and the S-(-) isomers, did not inhibit chloride conductance in rat extensor digitorum longus muscle fibers in vitro but, like clofibric acid and the S-(-) isomers, retained the serum cholesterol lowering activity in a cholesterol-fed rat model. Additionally, a stereoselective and greater inhibition was observed for the R-(+) isomers against adenosine diphosphate and arachidonic acid induced human platelet aggregation.

2-Methyl-4-chlorophenoxyacetic Acid↗
PubMed1987

Stereospecificity of the chloride ion channel: the action of chiral clofibric acid analogues.

2-(p-Chlorophenoxy)isobutyric acid (clofibric acid (1) or CPIB) is a drug known to block chloride membrane conductance (GCl) in rat striated muscle. In the present study chiral analogues of CPIB (2-(p-chlorophenoxy)propionic acid (2) and 2-(p-chlorophenoxy)butyric acid (3)) have been tested to evaluate the influence of chirality on Cl ion flux in the channel. The results showed that the chloride channel conductance strongly depends on the absolute configuration: in fact, the S-(-) isomers of the tested compounds strongly decreased the GCl of skeletal muscle membrane, whereas the R-(+) isomers were virtually ineffective. These data allow the hypothesis that, like other ion channels present in various biological systems, the chloride channel of skeletal muscle membrane could also have a stereospecific binding site (or receptor) regulating chloride ion flux.

2-Methyl-4-chlorophenoxyacetic Acid↗
PubMed1987

Correctly folded proteins make twice as many hydrophobic contacts.

A novel statistical analysis of non-bonded contacts in a set of known protein structures shows that the natural residue types fall into five or six groups distinguishable by nearest neighbor preference. The observed pattern of contact specificities clearly reflects residue hydrophobicity and charge. Its most striking feature is that residues in the hydrophobic group make about twice as many contacts with one another as would be expected on a random basis. A similar increase in hydrophobic contact frequency can be observed at the level of individual proteins. Native proteins make, on average, about twice as many hydrophobic contacts as corresponding misfolded proteins, generated by computer. On the basis of these observations increased hydrophobic contact frequency is proposed as a simple model of the hydrophobic effect.

Amino Acids↗
PubMed1986

Preliminary crystallographic X-ray data for an NAD(P)H:quinone reductase from mouse liver.

The hydrophilic form of NAD(P)H:(quinone acceptor) oxidoreductase (EC 1.6.99.2) from mouse liver cytosol has been crystallized in the presence of FAD. X-ray diffraction analysis showed these crystals to be tetragonal and to belong to the I422 space group. The unit cell measured a = b = 246.5 A and c = 70.4 A. Since the subunit molecular weight is 30,000, the asymmetric unit probably contains two pairs of dimers.

Animals↗