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Biomedical subjects

J W Walker

Publications and source records attributed to J W Walker.

At least 19 recordsLinked to original sources
PubMed1992

Effects of Ca2+ on the kinetics of phosphate release in skeletal muscle.

The process of phosphate dissociation during the muscle cross-bridge cycle has been investigated by photoliberation of inorganic phosphate (Pi) within skinned fibers of rabbit psoas muscle. This permitted a test of the idea that Ca2+ controls muscle contraction by regulating the Pi release step of the cycle. Photoliberation of Pi from structurally distinct "caged" Pi precursors initiated a rapid tension decline of up to 12% of active tension, and this was followed by a slower tension decline. The apparent rate constant of the fast phase, kPi, depended on both [Pi] and [Ca2+], whereas the slow phase generally occurred at 2-4 s-1. At maximal Ca2+, kPi increased in a nonlinear manner from 43 +/- 2 s-1 to 118 +/- 7 s-1, as Pi was raised from 0.9 to 12 mM. This was analyzed in terms of a three-state kinetic model in which a force-generating transition is coupled to Pi dissociation from the cross-bridge. As Ca(2+)-activated tension was reduced from maximal (Pmax) to 0.1 Pmax, (i) kPi decreased by up to 2.5-fold, (ii) the relative amplitude of the rapid phase increased 2-fold, and (iii) the relative amplitude of the slow phase increased about 6-fold. Changes in the rapid phase are compatible with Ca2+ influencing an apparent equilibrium constant for the force-generating transition. By comparison, kPi was faster than the rate constant of tension redevelopment, ktr, and was influenced less by Ca2+. Ca2+ effects on the caged Pi transient cannot account for the large effects of Ca2+ on actomyosin ATPase rates or cross-bridge cycling kinetics but may be a manifestation of reciprocal interactions between the thin filament and force-generating cross-bridges, and may represent Ca2+ regulation of the distribution of cross-bridges between non-force-and force-generating states.

Animals↗
PubMed1991

Visual development in the blepharophimosis syndrome.

One hundred and one cases of the blepharophimosis syndrome presenting over a decade are reviewed with particular attention to the factors influencing their visual development. Three distinct clinical patterns emerge--severe bilateral ptosis, moderate bilateral ptosis, and asymmetric ptosis--and their differing incidence of amblyopia and strabismus is discussed. The risk of amblyopia is much higher than previously believed (56.4% in our series) and preventive management is discussed.

Amblyopia↗
PubMed1991

Effect of level of intake and supplemental barley on marker estimates of fecal output using an intraruminal continuous-release chromic oxide bolus.

Sixty wethers (average BW = 45 kg) fitted with fecal collection bags were used in four experiments to evaluate the ability of a intraruminal continuous-release chromic oxide bolus to predict fecal DM output. In Exp. 1, 18 wethers housed in metabolism crates were fed barley at either 0, 100, or 200g/d and allowed ad libitum consumption of alfalfa pellets. In Exp. 2, 18 wethers were housed in metabolism crates and fed alfalfa pellets at either 70, 85, or 125% of pre-study ad libitum consumption. In Exp. 3, 12 wethers grazed a sagebrush-bunchgrass range and were individually fed barley at 0 or 200 g/d. In Exp. 4, 12 wethers grazed either an ungrazed (383 kg/ha herbaceous biomass) or a heavily grazed (175 kg/ha herbaceous biomass) sagebrush-bunchgrass range. Experiments 1 and 2 were balanced 3 x 3 Latin squares, and Exp. 3 and 4 were crossover designs. Chromium content was determined in rectal grab samples. Treatment effects were compared using marker-estimated fecal output divided by total fecal collection, multiplied by 100, as the dependent variable. Accuracy of the estimate was verified by comparing marker-estimated fecal output with total fecal collection using a paired t-test. In Exp. 1 and 2, treatments were different (P less than .05). No differences (P greater than .50) were detected in Exp. 3 and 4. In Exp. 1, 2, and 3 accuracy was different (P less than .02) among wethers within study and treatment. Only in Study 4 were minor or no differences (P greater than .09) in accuracy found.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗
PubMed1990

Kinetics of the conductance evoked by noradrenaline, inositol trisphosphate or Ca2+ in guinea-pig isolated hepatocytes.

1. Guinea-pig hepatocytes respond to noradrenaline (NA, 5-10 microM) with a large membrane conductance increase to K+ and Cl-. The response has a long initial delay (range 2-30 s). Following the delay, the K+ conductance (studied in Cl(-)-free solutions) rises quickly to a peak in 1-2 s and is maintained in the continued presence of NA, though often with superimposed oscillations of conductance. The roles of intracellular Ca2+ and D-myo-inositol 1,4,5-trisphosphate (InsP3) in this complex response have been investigated by rapid photolytic release of intracellular Ca2+ (from Nitr5-Ca2+ buffers) or InsP3 from 'caged' InsP3. 2. A rapid increase of intracellular [Ca2+] produced an immediate membrane conductance increase which rose approximately exponentially to a new steady level, consistent with a direct activation of Ca2(+)-dependent ion channels. 3. Following a pulse of InsP3, conductance rose after a brief delay (range 70-1500 ms) which was shortest at high [InsP3] or if the initial cytosolic [Ca2+] had been raised above normal levels. The maximum conductance produced by InsP3 was similar in each cell to the peak recorded with NA and could be evoked by InsP3 concentrations of 0.5-1 microM. 4. The rates of rise of conductance increased with InsP3 concentration in the range 0.25-12.5 microM (range 10-90%, rise times 90-1000 ms), indicating that InsP3-evoked Ca2(+)-efflux from stores increases with InsP3 concentration in this range. 5. Photochemically released InsP3 and Ca2+ activate at physiological concentrations the same membrane conductances as NA. The results indicate that the long initial delay in NA action occurs prior to or during generation of InsP3. The mechanism of the delay and the subsequent apparently all-or-none conductance increase during NA action are discussed in terms of the high co-operativity in InsP3 and Ca2+ actions and an additional positive feedback step. 6. Evidence was found of a negative interaction between [Ca2+] and InsP3-evoked Ca2+ release. The time course of the recovery of InsP3-evoked Ca2+ release following a rise of cytosolic [Ca2+] suggests that this interaction may be important in regulating oscillatory responses of [Ca2+] during hormonal stimulation of guinea-pig hepatocytes.

Action Potentials↗
PubMed1989

Photolabile precursors of inositol phosphates. Preparation and properties of 1-(2-nitrophenyl)ethyl esters of myo-inositol 1,4,5-trisphosphate.

1-(2-Nitrophenyl)ethyl esters of D-myo-inositol 1,4,5-trisphosphate (InsP3) have been synthesized and shown to have suitable properties for use as photolabile precursors of InsP3. Synthesis was accomplished by treatment of InsP3 with 1-(2-nitrophenyl)diazoethane in a CHCl3/water mixture. This resulted in esterification of each of the three phosphate residues in InsP3, the 1-phosphate being more reactive than the 4- or 5-phosphate. Singly esterified P-1, P-4, and P-5 esters, termed P-1, P-4, and P-5 caged InsP3, were isolated from the reaction mixture by anion-exchange HPLC and characterized by 500-MHz 1H NMR spectroscopy. Each of these caged InsP3 esters exists as a pair of diastereoisomers and was identified by examining the effects of pH and nitrophenyl ring current shielding on the chemical shifts of nonexchangeable inositol protons. 1H NMR spectra of InsP3 were analyzed for comparison. On photolysis the compounds released InsP3 with rate constants of 175 (P-1), 225 (P-4), and 280 s-1 (P-5) as determined by monitoring the aci-nitro decay reaction at pH 7.1, 0.2 M ionic strength, 21 degrees C. Quantum yields determined by steady-state near-UV photolysis were 0.65 +/- 0.08 for each compound. P-4 and P-5 caged InsP3 were the most promising biologically inactive InsP3 precursors since at concentrations up to 50 microM they did not release Ca2+ from smooth muscle sarcoplasmic reticulum (SR) and were not metabolized by vascular smooth muscle InsP3 5-phosphatase or bovine brain InsP3 3-kinase.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Synthesis, photochemistry, and biological activity of a caged photolabile acetylcholine receptor ligand.

A biologically inert photolabile precursor of carbamoylcholine has been synthesized; it is photolyzed to carbamoylcholine, a well-characterized acetylcholine analogue, with a half-time of 40 microseconds at pH 7.0 and a quantum yield of 0.8. The compound, N-(alpha-carboxy-2-nitrobenzyl)carbamoylcholine, was synthesized from (2-nitrophenyl)glycine. The photolysis rates (of five compounds) and the biological activity (of two compounds) were determined, and both properties were found to depend on the nature of the substituents on the photolabile protecting group. Laser pulse photolysis at wavelengths between 308 and 355 nm was used to investigate the wavelength dependence, quantum yield, and rate of the photolysis reaction. Photolysis products were isolated by high-performance liquid chromatography and identified by chemical and spectroscopic analysis and by their ability to activate the nicotinic acetylcholine receptor. BC3H1 muscle cells containing those receptors and a cell-flow method were used in the biological assays. The approach described may be useful in the preparation and characterization of other photolabile precursors of neurotransmitters that contain amino groups. The importance of these rapidly photolyzed, inert precursors of neurotransmitters is in chemical kinetic investigations of the reactions involving diverse neuronal receptors; such studies have been hampered because the available techniques have an insufficient time resolution.

Carbachol↗
PubMed1988

Inositol trisphosphate, calcium and muscle contraction.

The identity of organelles storing intracellular calcium and the role of Ins(1,4,5)P3 in muscle have been explored with, respectively, electron probe X-ray microanalysis (EPMA) and laser photolysis of 'caged' compounds. The participation of G-protein(s) in the release of intracellular Ca2+ was determined in saponin-permeabilized smooth muscle. The sarcoplasmic reticulum (SR) is identified as the major source of activator Ca2+ in both smooth and striated muscle; similar (EPMA) studies suggest that the endoplasmic reticulum is the major Ca2+ storage site in non-muscle cells. In none of the cell types did mitochondria play a significant, physiological role in the regulation of cytoplasmic Ca2+. The latency of guinea pig portal vein smooth muscle contraction following photolytic release of phenylephrine, an alpha 1-agonist, is 1.5 +/- 0.26 s at 20 degrees C and 0.6 +/- 0.18 s at 30 degrees C; the latency of contraction after photolytic release of Ins(1,4,5)P3 from caged Ins(1,4,5)P3 is 0.5 +/- 0.12 s at 20 degrees C. The long latency of alpha 1-adrenergic Ca2+ release and its temperature dependence are consistent with a process mediated by G-protein-coupled activation of phosphatidylinositol 4,5 bisphosphate (PtdIns(4,5)P2) hydrolysis. GTP gamma S, a non-hydrolysable analogue of GTP, causes Ca2+ release and contraction in permeabilized smooth muscle. Ins(1,4,5)P3 has an additive effect during the late, but not the early, phase of GTP gamma S action, and GTP gamma S can cause Ca2+ release and contraction of permeabilized smooth muscles refractory to Ins(1,4,5)P3. These results suggest that activation of G protein(s) can release Ca2+ by, at least, two G-protein-regulated mechanisms: one mediated by Ins(1,4,5)P3 and the other Ins(1,4,5)P3-independent. The low Ins(1,4,5)P3 5-phosphatase activity and the slow time-course (seconds) of the contractile response to Ins(1,4,5)P3 released with laser flash photolysis from caged Ins(1,4,5)P3 in frog skeletal muscle suggest that Ins(1,4,5)P3 is unlikely to be the physiological messenger of excitation-contraction coupling of striated muscle. In contrast, in smooth muscle the high Ins(1,4,5)P3-5-phosphatase activity and the rate of force development after photolytic release of Ins(1,4,5)P3 are compatible with a physiological role of Ins(1,4,5)P3 as a messenger of pharmacomechanical coupling.

Animals↗
PubMed1988

Relaxation of muscle fibers with adenosine 5'-[gamma-thio]triphosphate (ATP[gamma S]) and by laser photolysis of caged ATP[gamma S]: evidence for Ca2+-dependent affinity of rapidly detaching zero-force cross-bridges.

The relationship between the mechanical and biochemical states of the muscle cross-bridge cycle and the control of contraction were investigated by using the nucleotide analogs adenosine 5'-[gamma-thio]triphosphate (ATP[gamma S]) and caged ATP[gamma S] [the O-1(2-nitrophenyl)ethyl P3-ester of ATP[gamma S]]. ATP[gamma S] interacts with actomyosin in a manner similar to ATP but is hydrolyzed (by a factor of 500) more slowly. Generation of ATP[gamma S] by photolysis of caged ATP[gamma S] within a permeabilized fiber in rigor in the absence of Ca2+ relaxed tension and stiffness as occurs with ATP. The transient rise in tension prior to final relaxation observed with photolysis of caged ATP was absent with caged ATP[gamma S]. This result suggests that following detachment of a cross-bridge, ATP is normally hydrolyzed before force generation. In the presence of Ca2+, photolysis of caged ATP[gamma S] within rigor fibers caused tension to relax fully but significant stiffness remained. Stiffness also developed without concomitant tension when Ca2+ concentration was raised from less than 1 nM to 30 microM in the presence of ATP[gamma S]. The amplitude of the tension response to ramp stretches in the presence of Ca2+ and ATP[gamma S] increased with ramp stretch velocity, suggesting that the cross-bridges have detachment rate constants extending into the 10(3) s-1 range. The results provide evidence that the Ca2+-regulatory system can directly control attachment of cross-bridges into states before the power stroke.

Actomyosin↗
PubMed1987

Abdominal and pelvic pain.

Complaints of abdominal and pelvic pain account for a large number of Emergency Department presentations. Unfortunately, the subjective, often ambiguous, complaint of pain may represent a broad spectrum of pathology ranging from relatively benign disorders to acute, life-threatening illness. It is the duty of the Emergency Department physician to separate the potentially lethal disorders from the less acute illnesses, a task that this article aims to make easier.

Abdomen, Acute↗
PubMed1987

Reassessment of theophylline toxicity. Serum concentrations, clinical course, and treatment.

It has been reported in the medical literature that in cases of theophylline toxicity a relationship exists between the serum theophylline concentration and the severity of symptoms. We reviewed the records of 20 inpatients receiving long-term theophylline therapy who had serum theophylline concentrations of at least 20 mg/L (111 mumol/L) or who had symptoms of theophylline toxicity. No relationship between the serum concentrations and the severity of toxic effect was seen. Metabolic abnormalities similar to those previously reported in intentional acute intoxication were noted. Cardiac arrhythmias were seen in approximately half of the patients, hypotension in only one. No patient in whom a conservative form of therapy was initiated at diagnosis went on to develop additional toxic effects. It is our finding that severe toxic reactions to theophylline can occur over a wide range of serum concentrations. Conservative treatment measures, specifically drug discontinuation and interference with additional oral absorption by activated charcoal, should be instituted unless life-threatening symptoms are present, when more aggressive therapy (such as charcoal hemoperfusion) is warranted.

Aged↗
PubMed1986

Photolabile protecting groups for an acetylcholine receptor ligand. Synthesis and photochemistry of a new class of o-nitrobenzyl derivatives and their effects on receptor function.

Two compounds have been synthesized that feature a photosensitive o-nitrobenzyl moiety attached directly to the carbamate nitrogen of carbamoylcholine. The well-characterized acetylcholine analogue, carbamoylcholine, was released from these derivatives in response to laser light pulses at wavelengths between 300 and 355 nm. Photolysis products were isolated by high-performance liquid chromatography and identified by chemical and spectroscopic analysis. The yield of carbamoylcholine molecules per photon absorbed was 0.25. A short-lived photochromic intermediate in the photolysis reaction was detected by laser flash photolysis. A single laser flash induced an instantaneous increase in absorbance at 406 nm, followed by a first-order decay to products, with a half-time of 0.07 ms for one of the compounds [N-[1-(2-nitrophenyl)ethyl]carbamoylcholine iodide] in aqueous buffers at pH 7 and 23 degrees C. Decay rates and quantum yields depended on the nature of the substituent on the protecting group. Evidence is presented in support of the conclusion that the transient species is an aci-nitro intermediate that decays directly to carbamoylcholine and therefore determines its rate of release. The photosensitive carbamoylcholine derivatives activated the nicotinic acetylcholine receptor only after photolysis, as determined by 86Rb+ flux measurements with membrane vesicles prepared from Torpedo californica and Electrophorus electricus. Before photolysis, the compounds interacted weakly with the acetylcholine-binding sites as shown by competitive inhibition of acetylcholine-stimulated flux at high concentrations. The compounds did not induce receptor desensitization at a significant rate. The new compounds afford several major advantages over other photoactivatable acetylcholine analogues.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Methods for the detection of haemagglutinins in Aeromonas.

When grown in specified conditions and tested by a rocked-tile method, 40 of 41 isolates of two species of Aeromonas formed simultaneously at least two haemagglutinins among which were: (i) a mannose-sensitive haemagglutinins with strongest activity for guinea-pig or fowl red cells, formed by all of 31 isolates of A. hydrophila and 9 of 10 isolates of A. punctata ss. caviae; (ii) a haemagglutinin, sensitive to L-fucose or D-mannose, that reacted with human red cells and which was formed by all 41 isolates; and (iii) a mannose-resistant 'tanned red cell' haemagglutinin formed by 29 isolates of A. hydrophila and one isolate of A. punctata ss. caviae. Results emphasise that for the fullest possible identification of haemagglutinins produced by Aeromonas spp., strains should be cultured in a variety of conditions and tested with a wide range of red-cell species.

Aeromonas↗
PubMed1984

Effects of thio-group modifications of Torpedo californica acetylcholine receptor on ion flux activation and inactivation kinetics.

The effects of thio-group modifications on the ion permeability control and ligand binding properties of the acetylcholine receptor were measured in reconstituted membranes prepared from purified Torpedo californica acetylcholine receptor and soybean lipids (asolectin). A quench flow device was used to obtain subsecond time resolution for agonist-stimulated cation influx using carbamylcholine chloride (Carb) as the ligand and 86Rb+ as the cation. The effects of disulfide reduction with dithiothreitol (DTT), affinity alkylation with [4-(N-maleimido)benzyl]trimethylammonium ion and bromoacetylcholine, and nonspecific alkylation with N-ethylmaleimide and N-benzylmaleimide were examined. Activation, fast inactivation, and slow inactivation rates were measured on the chemically modified membranes. The flux results were compared with similar measurements on native membranes, and the role of vesicle size, heterogeneity, and influx time on ion flux results was analyzed. Major conclusions are that the binding sites that react with affinity labels are the same sites that mediate ligand-activated ion flux and that blockade of one of the two ligand binding sites is sufficient to block about 95% of the ion flux response. The main effect of DTT reduction is to shift the EC50 values for activation and slow inactivation to higher Carb concentrations, consistent with a decrease in binding affinity for Carb. The EC50 value for fast inactivation was not affected by DTT. However, the maximum rate of ion flux activation and the maximum rate of fast inactivation were decreased 2-fold after DTT treatment.

Animals↗
PubMed1984

Perfusion of the cerebral cortex by use of abdominal counterpulsation during cardiopulmonary resuscitation.

Perfusion of the cerebral cortex (rCCBF) during resuscitation from cardiac arrest was studied using 24 large dogs and three different resuscitation models. Conventional cardiopulmonary resuscitation (CPR) was compared with interposed abdominal compression CPR (IAC-CPR) and with IAC-CPR together with infusion of epinephrine. Conventional CPR produced a mean rCCBF of only 11% (0.057 +/- 0.07 ml/min/g) normal perfusion (0.54 +/- 0.14 ml/min/g). Even without epinephrine, IAC-CPR produced mean rCCBF equal to 51% (0.27 +/- 0.17 ml/min/g) of normal. With epinephrine, IAC-CPR produced rCCBF (0.93 +/- 0.49 ml/min/g) statistically indistinguishable from normal. Both models of IAC-CPR were significantly superior to conventional CPR in perfusion of the cerebral cortex.

Animals↗
PubMed1984

A multicentre comparison of piroxicam and indomethacin in acute soft tissue sports injuries.

One hundred and five patients suffering from sport-associated soft tissue injuries were included in a randomized controlled trial comparing the efficacy and side-effects of piroxicam and indomethacin. Patients were treated for 7 days. Both groups showed a similar degree of improvement in joint tenderness, swelling and pain. Eighty-eight per cent of patients on piroxicam showed a marked or moderate improvement in their injury at the end of the trial and 79% of indomethacin-treated patients. Approximately 50% of patients in both groups resumed full activity within 7 days. One patient, in the indomethacin group, was withdrawn from treatment due to a side-effect.

Athletic Injuries↗
PubMed1984

Differential efficacy of two non-steroidal anti-inflammatory drugs in the treatment of sports injuries.

Twenty-eight patients presenting with sports injuries were randomly allocated to receive either 200 mg sulindac twice daily or 400 mg ibuprofen 3-times daily. Pain symptoms (day and night ratings) and observer assessment of pain on movement, swelling and tenderness were recorded pre-treatment and after 3 and 7 days of therapy. One patient in the sulindac group was excluded from the study because initial symptoms were mild. Response, in terms of decrease in scores, was better in those receiving sulindac than in those given ibuprofen at both 3 and 7 days for the parameters of pain during the day (p less than 0.05 at 7 days) and pain on movement (p less than 0.05 at 3 days). Patient assessment of treatment at 3 and 7 days was significantly better in the sulindac group than in the ibuprofen group (p less than 0.025). The only reported side-effect was gastro-intestinal upset in a patient in the ibuprofen group. The results suggest that sulindac is an effective and well-tolerated treatment for the symptoms associated with sprain and strain injuries.

Adult↗