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D A Jones

Publications and source records attributed to D A Jones.

At least 127 records · Page 7Linked to original sources
PubMed1995

The metabolic costs of different types of contractile activity of the human adductor pollicis muscle.

1. The metabolic costs and physiological consequences of shortening contractions of a human muscle working in situ have been compared with those of the muscle maintaining a continuous isometric contraction and when performing repeated brief isometric contractions. 2. After a total of 10 s stimulation, the shortening and intermittent brief isometric protocols had very similar effects, causing a 30% loss of force and a threefold increase in the half-time of relaxation. This was in contrast to the continuous isometric contraction protocol where there was less than 10% loss of force or slowing of relaxation. 3. The ATP cost over the first 5 s of the continuous isometric protocol was 27 mmol (l intracellular water)-1 while for the shortening and repeated brief isometric protocols the costs were 48 and 46 mmol (l intracellular water)-1, respectively. 4. The results show that shortening and repeated brief isometric contractions are considerably more energetically demanding, and hence more fatiguing, than sustained isometric contractions.

Adenosine Triphosphate↗
PubMed1995

Characterization of the deamidase enzyme responsible for the metabolism of the anticancer peptide: H-Arg-D-Trp-NmePhe-D-Trp-Leu-Met-NH2.

H-Arg-D-Trp-NmePhe-D-Trp-Leu-Met-NH2, a broad spectrum neuropeptide growth factor antagonist (antagonist G), is soon to enter a phase I clinical trial for the treatment of small-cell lung cancer (SCLC). The pre-clinical pharmacology of this peptide has revealed that its metabolism proceeds from the C-terminus via deamidation. In this study the class of enzyme responsible for the degradation of antagonist G has been characterized. Tissue distribution studies on the enzyme have shown it to be very widespread with high specific activity being detected in the spleen, kidney, H69 SCLC xenograft and liver (12.64, 9.58, 8.00 and 6.94 nmols G/mg protein/hr, respectively). HPLC gel filtration indicated that the G-deamidase enzyme had an apparent molecular mass of 81 kDa. The sub-cellular distribution of the enzyme using differential centrifugation indicates that it is largely soluble with > 85% of the activity located in the cytosolic fraction. The distribution of activity towards antagonist G closely resembles that of esterase and acid carboxypeptidase activity, two activities, along with deamidase activity, known to be possessed by serine carboxypeptidases. Studies using a range of protease inhibitors showed clear inhibition of metabolism by phenylmethylsulphonylfluoride and benzyloxycarbonylphenylalanine chloromethylketone, indicating that the enzyme is a chymotrypsin-like serine carboxypeptidase. This knowledge of the enzyme will be invaluable in the further development of antagonist G and similar compounds. Moreover, the widespread distribution of this enzyme together with its broad specificity for C-terminal group suggests that it should be given serious consideration when designing C-terminally modified peptide drugs.

Amino Acid Sequence↗
PubMed1995

Processing of the neuropeptide growth factor antagonist [Arg6, D-Trp7.9, NmePhe8]-substance P (6-11) by a small cell lung cancer cell line (H69).

[Arg6, D-Trp7.9, NmePhe8]-substance P (6-11) (antagonist G) is a broad spectrum neuropeptide growth factor antagonist about to enter clinical trials as an anticancer drug. Its fate has been studied after incubation with two densities (5 x 10(4) cells/mL and 1 x 10(6) cells/mL) of the H69 small cell lung cancer cell line for up to 7 days at a concentration of 20 microM, corresponding to the IC50 for growth inhibition. HPLC analyses were conducted on cell pellets and media and in controls consisting of cell free media and water. Over 7 days in media containing cells a 70.4% reduction in parent peptide concentration occurred at the high density and a 44.1% reduction at low density. Despite this, there was a steady elevation in peptide associated with cells reaching a 189% increase by day 7. Oxidation of G at the C-terminal methionine residue occurred in all media studied indicative of a chemical process. The two major active metabolites of antagonist G (deamidated G and G minus Met11) were detected only in media in the presence of cells. These accumulated with time in media and cells together with oxidized products. These results reveal complex cellular pharmacology for antagonist G where H69 cells are increasingly exposed to 4 different peptide products rather than 1.

Antineoplastic Agents↗
PubMed1995

Convergence of angiotensin II and platelet-derived growth factor receptor signaling cascades in vascular smooth muscle cells.

Signaling cascades elicited by angiotensin II resemble those characteristic of growth factor stimulation. In this report, we demonstrate that angiotensin II converges with platelet-derived growth factor (PDGF) beta-receptor signaling cascades, independent of PDGF. Stimulation of smooth muscle cells with angiotensin II resulted in tyrosine phosphorylation on Shc proteins and subsequent complex formation between Shc and growth factor receptor binding protein-2 (GRB2). A 180-kDa protein co-precipitating with Shc.GRB2 complexes also demonstrated increased phosphorylation in response to angiotensin II. Immunoblot analyses and proteolytic digests failed to distinguish this 180-kDa protein from authentic PDGF beta-receptors. Corresponding with Shc and PDGF receptor phosphorylation induced by angiotensin II was the recruitment and phosphorylation of c-Src. Autocrine release of platelet-derived growth factor failed to account for Shc complex formation at the PDGF receptor following angiotensin II treatment, and a specific angiotensin II type I receptor antagonist, losartan, abolished the response. These results support a novel model for cross-talk between the G-protein-linked angiotensin II receptor and the PDGF receptor tyrosine kinase in vascular smooth muscle cells. Communication with the PDGF receptor may account for the ability of angiotensin II to elicit responses typical of growth factor signal transduction.

Adaptor Proteins, Signal Transducing↗
PubMed1995

Fatigue and recovery of voluntary and electrically elicited dynamic force in humans.

1. Percutaneous electrical stimulation of the human quadriceps muscle has been used to assess the loss of central activation immediately after a bout of fatiguing exercise and during the recovery period. 2. Fatigue was induced in eight healthy males by a maximal effort lasting 25 s performed on an isokinetic cycle ergometer at a constant pedal frequency of 60 revolutions per minute. The cranks of the ergometer were driven by an electric motor. Before and after the sprint, subjects allowed their legs to be passively taken round by the motor. During the passive movement the knee extensors were stimulated (4 pulses; 100 Hz). Peak voluntary force (PVF) during the sprint and peak stimulated forces (PSF) before and in recovery were recorded via strain gauges in the pedals. Recovery of voluntary force was assessed in a series of separate experiments in which subjects performed a second maximal effort after recovery periods of different durations. 3. Peak stimulated forces were reduced to 69.8 +/- 9.3% immediately after the maximal effort, (P < 0.05), but had returned to pre-exercise values after 3 min. The maximum rate of force development (MRFD) was also reduced following fatigue to 68.8 +/- 11.0% (P < 0.05) of control and was fully recovered after 2 min. PVF was reduced to 72.0 +/- 9.4% (P < 0.05) of the control value following the maximal effort. After 3 min voluntary force had fully recovered. 4. The effect of changing the duration of the fatiguing exercise (10, 25 and 45 s maximal effort) resulted in an increased degree of voluntary force loss as the duration of the maximal effort increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Loss of power during fatigue of human leg muscles.

1. We have investigated the loss of power seen during high-intensity exercise of human leg muscles such as might occur during sprinting. Subjects exercised the quadriceps and hamstring muscle groups using a Cybex dynamometer at an angular velocity of 90 deg s-1 once a second for 6 min. At 1 min intervals the quadriceps were electrically stimulated via the femoral nerve to produce an isometric contraction which was then released into an isokinetic shortening contraction at 90 deg s-1. 2. The extent of central fatigue was assessed by comparing the force of a voluntary isokinetic contraction with that elicited by electrical stimulation during isokinetic releases. Two subjects were repeatedly tested. In the first series of experiments, exercising the quadriceps of one leg, the instantaneous power fell to about 50% over the course of 2 min and remained constant for the rest of the exercise. For one subject the voluntary and electrically stimulated forces declined in parallel while for the second subject the voluntary force was 10% less than the stimulated force at the end of the exercise. These results show that central fatigue represented a minor factor contributing no more than one-fifth of the total loss of power in these circumstances. 3. In a second series of experiments the subjects alternately contracted the quadriceps and the hamstrings of both legs in an exercise which had a high rating of perceived exertion and entailed considerable respiratory and cardiovascular effort. The time course and proportionate loss of power were very similar to those seen with the one-leg exercise and neither subject showed evidence of significant central fatigue. The pattern of force loss was very similar for the hamstrings. We conclude that, for determined subjects, afferent feedback from muscles, tendons and joints or from the respiratory and cardiovascular systems does not have a major role in inhibiting voluntary activation of the quadriceps during heavy exercise. 4. In both series of experiments the power output during electrically stimulated isokinetic contractions was reduced to 50% of the initial value after 2 min of exercise while the isometric force, measured immediately before the release, fell to only 75%. This suggests that fatigue affects isometric and shortening contractions to different extents and the loss of power may be due to a combination of factors, only one of which is evident in the loss of isometric force.

Adult↗
PubMed1995

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Copyright↗
PubMed1995

The significance of motor unit variability in sustaining mechanical output of muscle.

Neuromuscular function and fatigue have been studied using a wide variety of preparations. These range from sections of single fibers from which the cell membrane has been removed to whole muscles or groups of muscles acting about a joint in the intact animal. Each type of preparation has its merits and limitations. There is no ideal preparation; rather the question to be answered will determine the most appropriate model in each case and sometimes a combination of approaches will be needed. In particular, it is important to understand how the mechanical output of whole muscle can be sustained to meet the demands of a task and to take into account the organized variability of the constituent motor units.

Animals↗
PubMed1995

Metabolism of the anticancer peptide H-Arg-D-Trp-NmePhe-D-Trp-Leu-Met-NH2.

H-Arg-D-Trp-NmePhe-D-Trp-Leu-Met-NH2 (Antagonist G) will be the first broad-spectrum neuropeptide antagonist to enter a phase I clinical trial. Its in vitro and in vivo metabolism has been extensively characterized. The major metabolites were identified and their structures elucidated by mass spectroscopy and amino acid analysis. Metabolism occurred almost exclusively at the C-terminus and was arrested by phenylmethylsulfonylfluoride, a known serine-protease inhibitor. Biological characterization of the metabolites demonstrated that the degradation of Antagonist G produces metabolites that retain neuropeptide antagonist properties.

3T3 Cells↗
PubMed1995

31P nuclear magnetic resonance spectroscopy of acutely ischaemic limbs: the extent of changes and progress after reconstructive surgery.

31P Nuclear magnetic resonance (NMR) spectroscopy of the tibialis anterior muscle was carried out on nine acutely ischaemic limbs in eight patients before and after revascularization, in 15 limbs of 13 claudicants at rest, in 17 patients with normal lower limb circulation suffering chronic renal failure, and in six healthy subjects. Claudicants, renal failure and healthy limbs showed similar inorganic phosphate/phosphocreatine ratios (Pi/PCr). Healthy volunteers after 30-min tourniquet ischaemia and patients with acutely ischaemic limbs showed significantly raised Pi/PCr ratios (P < 0.05). There was an association between Pi/PCr ratios and the systolic ankle:brachial pressure index in acutely ischaemic limbs. In the acute patients, the Pi/PCr ratios returned to normal after successful revascularization, the time course varying between 3 days and 3 months. Intracellular acidosis was observed in one patient who was also the only individual to develop reperfusion injury following reconstructive surgery. Acidosis may be a sign of muscle changes which lead to reperfusion injury.

Adult↗
PubMed1995

Identification of amplified restriction fragment polymorphism (AFLP) markers tightly linked to the tomato Cf-9 gene for resistance to Cladosporium fulvum.

Using the technique of amplified restriction fragment polymorphism (AFLP) analysis, and bulked segregant pools from F2 progeny of the cross Lycopersicon esculentum (Cf9) x L. pennellii, approximately 42,000 AFLP loci for tight linkage to the tomato Cf-9 gene for resistance to Cladosporium fulvum have been screened. Analysis of F2 recombinants identified three markers which co-segregated with Cf-9. The Cf-9 gene has recently been isolated by transposon tagging using the maize transposon Dissociation (Ds). Analysis of plasmid clones containing Cf-9 shows that two of these markers are located on opposite sides of the gene separated by 15.5 kbp of intervening DNA. AFLP analysis provides a rapid and efficient technique for detecting large numbers of DNA markers and should expedite plant gene isolation by positional cloning and the construction of high-density molecular linkage maps of plant genomes.

Base Sequence↗
PubMed1995

Distribution of unlinked transpositions of a Ds element from a T-DNA locus on tomato chromosome 4.

In maize, receptor sites for unlinked transpositions of Activator (Ac) elements are not distributed randomly. To test whether the same is true in tomato, the receptor sites for a Dissociation (Ds) element derived from Ac, were mapped for 26 transpositions unlinked to a donor T-DNA locus on chromosome 4. Four independent transposed Dss mapped to sites on chromosome 4 genetically unlinked to the donor T-DNA, consistent with a preference for transposition to unlinked sites on the same chromosome as opposed to sites on other chromosomes. There was little preference among the nondonor chromosomes, except perhaps for chromosome 2, which carried seven transposed Dss, but these could not be proven to be independent. However, these data, when combined with those from other studies in tomato examining the distribution of transposed Acs or Dss among nondonor chromosomes, suggest there may be absolute preferences for transposition irrespective of the chromosomal location of the donor site. If true, transposition to nondonor chromosomes in tomato would differ from that in maize, where the preference seems to be determined by the spatial arrangement of chromosomes in the interphase nucleus. The tomato lines carrying Ds elements at known locations are available for targeted transposon tagging experiments.

Base Sequence↗
PubMed1995

Pharmacokinetics, metabolism, tissue and tumour distribution of the neuropeptide growth factor antagonist [Arg6, D-Trp7,9, NmePhe8]- substance P(6-11) in nude mice bearing the H69 small-cell lung cancer xenograft.

BACKGROUND: [Arg6, D-Trp7,9, NmePhe8]-Substance P (6-11) (codenamed antagonist G) represents the first board spectrum antagonist of a number of neuropeptides shown to act as growth factors in small-cell lung cancer (SCLC) and is shortly to enter clinical trials. DESIGN: Pharmacokinetics, metabolism, tissue disposition have been studied in mice (nu/nu) bearing the NCI-H69 human SCLC xenograft after systemic drug adminstration at an active dose (45 mg/kg i.p.). RESULTS: The peptide exhibited relatively long half life (28.9 min; clearance 45.6 ml/min/kg) and distributed widely (volume of distribution 1490 ml/kg). Marked accumulation of antagonist G (and its metabolites) was noted in the liver (AUC5278 micrograms/g x min) and to a lesser extent the spleen (AUC 930 micrograms/g x min) but only low levels appeared to cross the blood brain barrier (AUC in brain, 20 micrograms/g x min) or be taken up into the heart (AUC 101 micrograms/g x min). Tumour uptake was intermediate in value out of the 7 tissues studied (AUC 195 micrograms/g x min). Metabolism was restricted almost exclusively to the C terminal of the peptide producing 4 major products: M1, deamidated antagonist G; M2, Harg-DTrp-NmePhe-DTrp-Leu-OH, both of which retain growth factor antagonist activity; M3, a combination of oxidised antagonist G [Met11(O)] and oxidised deamidated antagoinst G; and M4, a combination of H-Arg-DTrp-NmePhe-DTrp-OH and H-DTrp-NmePhe-DTrp-Leu-OH. Extensive biotransformation to predominately M1 and M2 occurred in most tissues including the tumour where the parent peptide accounted for only 48.5% of the total. CONCLUSION: Levels of antagonist G required to produce a small but significant effect on the growth of SCLC cell lines in vitro are in the region of 4-7 microM. Taking into account metabolites, a peak concentration of 4.1 microgram/g (4.3 microM) was achieved in the H69 xenograft. These studies reveal a favourable preclinical pharmacology profile for antagonist G and offer hope that anticancer activity may be achievable in man.

Animals↗
PubMed1995

Modular unipolar versus bipolar prosthesis: a prospective evaluation of functional outcome after femoral neck fracture.

Between January 1, 1987, and December 31, 1992, 140 community-dwelling geriatric patients > or = 65 years of age with a displaced femoral neck fracture (Garden III-IV) underwent primary prosthetic replacement and were followed prospectively for a minimum of 1 year. Overall, 92 patients received a cemented bipolar prosthesis and 48 patients received a cemented modular unipolar prosthesis. There were no statistically significant differences between the two groups with respect to preinjury characteristics (age, sex, and number and severity of medical comorbidities) and functional ability. There were no statistically significant differences between the two groups with regard to the number of postoperative complications, length of stay, and 1 year mortality rate. An in-depth functional evaluation was obtained as follows: level of ambulation, independence in basic activities of daily living (feeding, bathing, dressing, toileting), and independence in instrumental activities of daily living (food shopping, food preparation, banking, laundry, housework, and use of public transportation). At 1 year follow-up, no statistically significant differences in functional ability were identified between the unipolar and bipolar groups. Furthermore, at a minimum of 1 year follow-up, there were no statistically significant differences between the two groups with regard to the need for revision surgery or the incidence hip pain. Based on the results of this study, there does not appear to be any advantage to the use of bipolar endoprosthesis for the treatment of femoral neck fractures in the elderly patient. The lower cost of modular unipolar prostheses compared with bipolar prostheses provides additional support for their use.

Aged↗
PubMed1995

Immunodominant autoepitopes of type VII collagen are short, paired peptide sequences within the fibronectin type III homology region of the noncollagenous (NC1) domain.

Autoantibodies to type VII collagen are associated with the blistering diseases epidermolysis bullosa acquisita and bullous systemic lupus erythematosus. We showed previously that these autoantibodies recognize epitopes within the noncollagenous (NC1) region of type VII collagen. That region is composed of fibronectin type III homology units that may contribute to intermolecular cross-linking and basement membrane adhesion functions of type VII collagen. In this study, we defined the specific amino acid sequences recognized by these autoantibodies. By fusion protein analysis, sera from patients with epidermolysis bullosa acquisita and bullous lupus were found to react with two regions within the fourth (E-1) and eighth (E-2) fibronectin homology repeats, each consisting of approximately 100 amino acids. Affinity purification studies showed E-1 and E-2 to be independent and non-cross-reactive epitope regions. These regions were probed further by enzyme-linked immunosorbent assay analysis of overlapping octapeptide sets derived from the amino acid sequences of E-1 and E-2. The results showed two reactive, closely associated octapeptide sequences within each region, both lying in amphipathic portions of fibronectin type III homology repeats. These studies identify short peptide sequences within the NC1 domain of type VII collagen that are targeted independently by autoantibodies. These sequences may play a direct role in determining the properties of type VII collagen that influence adhesion between this molecule and other basement membrane proteins, and their alteration by antibody binding may be the immunopathogenic event underlying epidermolysis bullosa acquisita and bullous lupus.

Amino Acid Sequence↗
PubMed1995

Glyburide attenuates calmodulin antagonist-stimulated renin release from isolated mouse juxtaglomerular cells.

Previous reports have shown that K+ channel openers elevate plasma renin activity in vivo and stimulate renin release (RR) from juxtaglomerular (JG) cells in vitro. Therefore, we examined whether the K+ channel blocker, glyburide, inhibits basal RR or RR stimulated by elevating cAMP or by inhibiting Ca2+/calmodulin activity in cultures of isolated mouse JG cells. Glyburide treatment (10-300 microM) had no effect on basal RR, which measured approximately 10% or 30% of the total cellular renin activity after 4 or 24 h, respectively. RR stimulated by elevating cAMP with isoproterenol, forskolin, or 3-isobutyl-1-methylxanthine was also unaffected by glyburide. In contrast, glyburide significantly attenuated RR stimulated by the calmodulin antagonists, calmidazolium, trifluoperazine, and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7). Calmidazolium-stimulated RR returned to basal levels with 100 microM glyburide cotreatment. Blockade of voltage-gated calcium channels with verapamil or inhibition of calcium release from intracellular stores with 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester (TMB-8) had no effect on the ability of glyburide to attenuate calmidazolium-stimulated RR. However, lowering of the extracellular calcium concentration by the addition of EGTA abolished the inhibitory effects of glyburide. We conclude that modulation of K+ channels may influence RR by affecting Ca2+/calmodulin-regulated secretion, but not cAMP-mediated secretion, from JG cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Oxidatively modified LDL contains phospholipids with platelet-activating factor-like activity and stimulates the growth of smooth muscle cells.

Oxidative modification of lipoproteins is believed to be important in the genesis of atherosclerosis. We established cultures of smooth muscle cells (SMC) and exposed them to native LDL or oxidized LDL. Oxidized LDL, but not native LDL, was mitogenic as measured by incorporation of [3H]-thymidine into DNA. This effect was concentration dependent, averaged 288% of control, and was blocked by a platelet-activating factor (PAF) receptor antagonist. We hypothesized that phospholipids with PAF-like activity were generated during the oxidation of LDL. To test this hypothesis we extracted phospholipids from copper-oxidized LDL and assayed for PAF-like activity. Phospholipids extracted from oxidized LDL and purified by HPLC induced neutrophil adhesion equivalent to PAF (10 nM) and were mitogenic for smooth muscle cells. These effects were not seen with phospholipids extracted from native LDL and were blocked by two structurally different, competitive antagonists of the PAF receptor. The effects of these lipids were also abolished by pretreating them with PAF acetylhydrolase. Finally, we used Chinese hamster ovary cells that had seen stably transfected with a cDNA for the PAF receptor to confirm that phospholipids from oxidized LDL act via this receptor. We found that PAF (control) and the oxidized phospholipids each induced release of arachidonic acid from the transfected cells, but had no effect on wildtype Chinese hamster ovary cells, which lack the PAF receptor. This effect was also blocked by a PAF receptor antagonist. Thus, phospholipids generated during oxidative modification of LDL may participate in atherosclerosis by stimulating SMC proliferation and leukocyte activation.

Animals↗