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Biomedical subjects

D J Nelson

Publications and source records attributed to D J Nelson.

At least 109 records · Page 6Linked to original sources
PubMed1989

Treatment of American cutaneous leishmaniasis with orally administered allopurinol riboside.

Eighteen patients received 1,250 mg of allopurinol riboside (AR) four times daily for 28 d. Nine of the patients concurrently received 500 mg probenecid (PB) four times daily. Cure was assessed clinically and parasitologically. Patients who had culture-positive and nonhealing lesions 3 mo after therapy received pentavalent antimony. Of the nine patients who received AR alone, four (44%) had clinical improvement at the end of therapy and two (22%) were culture-negative. A third patient became culture negative at 2 mo after therapy. The culture-negative patients were completely healed at 1 mo and remained so at 1 y after therapy. Of the nine patients who received AR plus PB, four had complete healing and two had clinical improvement at the end of therapy; however, all patients remained culture-positive. At 2-3 mo after therapy, six (67%) of the patients were completely healed, and of these, five (56%) were culture-negative. The drug was well-tolerated.

Adult↗
PubMed1989

Effects of a monoclonal anti-acetylcholine receptor antibody on the avian end-plate.

1. The effects of anti-acetylcholine receptor (AChR) monoclonal antibodies (mAbs) 370 and 132A on miniature end-plate potentials (MEPPs) and end-plate currents (EPCs) in the posterior latissimus dorsi muscle of adult chickens were investigated. 2. After incubation of the electrophysiological preparation with mAb 370 (5-50 micrograms/ml), which blocks both agonist (carbamylcholine) and alpha-bungarotoxin (alpha-BTX) binding and induces a hyperacute form of experimental autoimmune myasthenia gravis (EAMG), MEPP and EPC amplitudes were irreversibly reduced. 3. This effect was not associated with any significant change in the time constant describing EPC decay (tau EPC), current reversal potential, or the voltage dependence of tau EPC. The tau EPC at -80 mV was 5.9 +/- 0.6 ms before incubation with mAb 370 (50 micrograms/ml) and 6.0 +/- 0.9 ms afterwards. Current reversal potential was -3.9 +/- 0.4 mV before mAb incubation and -4.8 +/- 1.5 mV afterwards. The change in membrane potential required to produce an e-fold change in tau EPC was 128 +/- 2.3 mV before antibody incubation compared to 125 +/- 6.6 mV after incubation. 4. A second anti-AChR mAb, 132A (50 micrograms/ml), which is capable of inducing the classically described form of EAMG without blocking agonist or alpha-BTX binding, or inducing hyperacute EAMG, produced no significant change in MEPP amplitude, EPC amplitude, tau EPC or EPC reversal potentials. 5. The mAb 370 (50 micrograms/ml) induced a partially reversible decrease of the quantal content of the neurally evoked end-plate potential (EPP). This effect was not observed with mAb 132A, (+)tubocurarine (10(-7)-10(-5) g/ml) or an irrelevant anti-oestrogen receptor mAb. 6. These data suggest that the rapid onset of weakness observed in chicken hatchlings after the injection of mAb 370 (Gomez & Richman, 1983) can be attributed to a combined effect of a block of acetylcholine (ACh)-induced ion channel activity in the postsynaptic membrane and a reduction of the neurally evoked release of acetylcholine from the nerve terminal.

Action Potentials↗
PubMed1989

Expression and modulation of K+ currents in oligodendrocytes: possible role in myelinogenesis.

We have used whole-cell and single-channel recording techniques to investigate the electrophysiological properties of cultured ovine oligodendrocytes (OLGs). Our studies have led to the following conclusions. (1) Cultured mature OLGs express a variety of voltage-dependent K+ conductances including an outward current that consists of a transient component and a steady-state component, as well as an inwardly rectifying K+ current. (2) These conductances are expressed sequentially as a function of development in culture. The inwardly rectifying K+ current appears later than the outward current. (3) Although process extension may influence the expression of the ion channels, the majority of the K+ channels are located in the soma of OLGs, probably concentrated in the basal plasma membrane. (4) Finally, the activation of K+ channels in OLGs can be inhibited by two distinct second messengers, cAMP acting through protein kinase A and diacylglycerol acting through protein kinase C, the effects of which perhaps converge at the level of a common phosphorylated enzyme or regulatory protein. Both cAMP and diacylglycerol have been implicated as factors important in controlling the induction of a myelinogenic metabolism associated with OLG substratum attachment. Thus, membrane ion channels may provide an important intermediate step linking cellular substratum attachment to the eventual induction of myelinogenesis.

Animals↗
PubMed1988

Effects of 3'-azido-3'-deoxythymidine on the deoxynucleotide triphosphate pools of cultured human cells.

The effects of 3'-azido-3'-deoxythymidine (AZT) on the deoxynucleotide pools of three human cell lines, HL-60, H-9, and K-562, were determined. The corresponding ED50s for inhibition of cell growth were 670, 100, and 100 microM AZT. In all three lines, exposure to 200 microM AZT caused dTTP and dGTP initially to fall and then to return towards control levels. In contrast to a previous report [Furman et al., (1986) Proc. Nat. Acad. Sci. USA 83, 8333-8337], dCTP levels increased. Pools of dATP were relatively unchanged. Qualitatively similar changes occurred in 10 microM AZT, but recovery was faster than at 200 microM AZT. After 24 hrs incubation with 200 microM AZT, AZT-5'-MP reached 2.8, 4.7, and 15.7 mM in the HL-60, H-9, and K-562 cells, respectively. When HL-60 and K-562 cells incubated in AZT were resuspended in fresh medium, AZT-5'-MP pools declined with respective t1/2 values equal to 34 and 68 min. The concentration of thymidine, and to a lesser extent deoxyuridine, increased in the media of treated cells. AZT-5'-MP was found in the media of cells treated with AZT.

Antiviral Agents↗
PubMed1988

Changes in respiratory burst activity during human monocyte differentiation in suspension culture.

Monocytes undergo a process of differentiation following their accumulation into extravascular spaces. This process has been examined previously by culturing monocytes and identifying changes in cell morphology, metabolism, and function over time. The present study was designed to characterize mononuclear phagocyte respiratory burst activity as related to differentiation by measuring chemiluminescence and superoxide anion generation in cultured human monocytes. Monocytes maintained in Teflon vials for up to 12 days increased in size, were positive for nonspecific esterase, and retained the ability to ingest latex particles. During culture, however, cells progressively lost their peroxidase-positive granules. When monocytes were cultured for one or five days, they elicited less than 50% of the luminol-enhanced chemiluminescence produced by fresh monocytes following PMA stimulation. By day 7, less than 20% of day 0 PMA-elicited chemiluminescence was observed. A comparable loss of serum-opsonized zymosan-induced chemiluminescence occurred during monocyte culture. Since it is recognized that luminol-enhanced chemiluminescence is, in large part, dependent upon myeloperoxidase and since differentiated mononuclear phagocytes are only minimally peroxidase-positive, cultured monocyte respiratory burst activity was also assessed by directly quantifying superoxide anion generation. When monocytes were cultured for three or five days, they elicited 38% more superoxide anion than did fresh monocytes following PMA stimulation. At day 7, PMA-induced superoxide anion release was comparable to day 0 levels. These data indicate that monocytes allowed to differentiate under nonadherent conditions maintain the ability to undergo a respiratory burst response as measured by superoxide anion release, but they concomitantly lose peroxidase-dependent luminol-enhanced chemiluminescence. In this regard, monocytes cultured in suspension metabolically resemble macrophages that have undergone differentiation within sites of inflammation.

Cell Differentiation↗
PubMed1988

Forskolin and phorbol esters decrease the same K+ conductance in cultured oligodendrocytes.

Cultured ovine oligodendrocytes (OLGs) express a number of voltage-dependent potassium currents after they attach to a substratum and as they begin to develop processes. At 24-48 hours following plating, an outward potassium current can be identified that represents a composite response of a rapidly inactivating component and a steady-state or noninactivating component. After 4-7 days in culture, OLGs also develop an inward rectifier current. We studied the effects of forskolin and phorbol 12-myristate 13-acetate (PMA) on OLG outward currents. These compounds are known to alter the myelinogenic metabolism of OLGs. PMA, an activator of protein kinase C (PK-C), has been shown to enhance myelin basic protein phosphorylation while forskolin acting on adenylate cyclase, and thereby increasing cAMP, inhibits it. Both forskolin and PMA increase the phosphorylation of 2'3'-cyclic nucleotide phosphodiesterase, an OLG/myelin protein. We found that forskolin decreased the steady-state outward current at 120 mV by 10% at 100 nM, and by 72% at 25 microM from a holding potential of -80 mV. The time course of inactivation of the peak currents was decreased, affecting both the fast and slow time constants. There was no significant change in the steady-state parameters of current activation and inactivation. The effect of forskolin was attenuated when the adenylate cyclase inhibitor adenosine (2 mM) was present in the intracellular/pipette filling solution. The results of PMA experiments were similar to those obtained with forskolin. Whereas the amplitude of the currents in the presence of PMA was reduced by 28% at 1.5 nM and 60% and 600 nM, the decay phase of the peak currents was less affected. The PMA effect could still be seen when the intracellular Ca2+ was reduced to less than or equal to 10 nM with 5 mM BAPTA, but was inhibited when the cells were pre-exposed to 50 microM psychosine, a PK-C inhibitor. It is postulated that the potassium currents in OLG can be physiologically modulated by two distinct second-messenger systems, perhaps converging at the level of a common phosphorylated enzyme or regulatory protein.

Animals↗
PubMed1988

Interactions of spin-labeled calmodulin with trifluoperazine and phosphodiesterase in the presence of Ca(II), Cd(II), La(III), Tb(III), and Lu(III).

Bovine calmodulin analogues, spin-labeled at methionine and tyrosine residues, have been utilized in electron paramagnetic resonance (EPR) studies designed to investigate calmodulin interactions with the antipsychotic drug trifluoperazine and the calmodulin-binding protein 3',5'-cyclic nucleotide phosphodiesterase. Trifluoperazine titrations of spin-labeled calmodulin analogues were carried out in the presence of Ca(II), Cd(II), and Tb(III). Similar experiments were performed with the phosphodiesterase in the presence of Ca(II), Cd(II), La(III), Tb(III), and Lu(III). EPR signals from the methionine-directed probe proved to be more sensitive to the binding of target molecules than signals from the tyrosine-directed probe, perhaps indicating that the spin-labeled methionine is at a site close to the target molecule binding site. While the binding of TFP, as monitored by EPR spectral changes in the methionine spin-labeled calmodulin, was in evidence with Ca(II), Cd(II), and all the lanthanides examined, no binding of phosphodiesterase to calmodulin could be detected in the presence of the lanthanide ions, perhaps due to inactivation of the phosphodiesterase by lanthanide ion binding. The abilities of the spin-labeled calmodulins to activate phosphodiesterase were also investigated. The spin-labeled tyrosine calmodulin was able to activate phosphodiesterase as well as native calmodulin, while a lower degree of activation was found when the spin-labeled methionine analogue was used.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1988

Expression of a Drosophila melanogaster acetylcholine receptor-related gene in the central nervous system.

We isolated Drosophila melanogaster genomic sequences with nucleotide and amino acid sequence homology to subunits of vertebrate acetylcholine receptor by hybridization with a Torpedo acetylcholine receptor subunit cDNA probe. Five introns are present in the portion of the Drosophila gene encoding the unprocessed protein and are positionally conserved relative to the human acetylcholine receptor alpha-subunit gene. The Drosophila genomic clone hybridized to salivary gland polytene chromosome 3L within region 64B and was termed AChR64B. A 3-kilobase poly(A)-containing transcript complementary to the AChR64B clone was readily detectable by RNA blot hybridizations during midembryogenesis, during metamorphosis, and in newly enclosed adults. AChR64B transcripts were localized to the cellular regions of the central nervous system during embryonic, larval, pupal, and adult stages of development. During metamorphosis, a temporal relationship between the morphogenesis of the optic lobe and expression of AChR64B transcripts was observed.

Amino Acid Sequence↗
PubMed1988

Voltage-gated potassium currents in cultured ovine oligodendrocytes.

Cultured oligodendrocytes (OLGs) develop processes and form myelin following attachment to a substratum. We applied the whole-cell voltage-clamp technique to identify and characterize the ionic currents of OLGs in culture. Within 2 d after attachment, OLGs extended processes and began to express an outward current that represents a composite response of an inactivating/transient component and a non-inactivating component. The current had a reversal potential of -66 mV and was sensitive to potassium channel blockers. After 4-5 d in culture, the transient component was less prominent, often accompanied by an increase in noninactivating or steady-state outward current. In addition, there was an increase in inward rectifier current. Four of 7 cells that failed to develop processes exhibited only linear high-resistance membranes. We conclude that cultured OLGs express 3 voltage-gated potassium conductances: (1) a transient outward current, (2) a noninactivating outward current, and (3) an inward rectifier current. The sequential appearance of the several currents may relate, at least in part, to process formation.

4-Aminopyridine↗
PubMed1987

The inhibitory effects of K+ channel-blocking agents on T lymphocyte proliferation and lymphokine production are "nonspecific".

The effect of K+ channel-blocking agents, tetraethylammonium (TEA) and 4-aminopyridine (4AP), on the responses of cloned murine helper and cytolytic T lymphocytes stimulated with mitogen, anti-T cell receptor monoclonal antibody, or interleukin 2 was examined. The addition of TEA and 4AP reduced [3H]thymidine incorporation and lymphokine production to levels observed in unstimulated cells. However, thymidine incorporation by the tumor cell lines P-815 and SP2/0, which replicate autonomously, also was inhibited by these drugs. Treatment of cloned murine helper T lymphocyte, L2, with TEA appeared to inhibit uptake of [3H]thymidine and [3H]phenylalanine after stimulation with interleukin 2. These results suggest that the inhibitory effects of the K+ channel-blocking agents TEA and 4AP may not be specific for the sequence of events that are initiated by activation of T lymphocytes through the antigen receptor. Instead, the observed inhibitory effects by these agents may result from inhibition of transport of thymidine, amino acids, and other essential metabolites across the cell membrane.

4-Aminopyridine↗
PubMed1987

Antigiardial activity of guanine arabinoside. Mechanism studies.

Guanine arabinoside (araG) inhibited the in vitro growth of Giardia lamblia WB with an ED50 value of 4 microM. The inhibition was prevented completely by 2'-deoxyguanosine, prevented partially by guanine and guanosine, and not prevented by adenine, adenosine or 2'-deoxyadenosine. Extracts of G. lamblia grown in the presence of [8-3H]araG contained radiolabeled araGMP, araGDP and araGTP. The formation of araGTP during the exponential phase of cell growth increased with time and was dependent upon the araG concentration. AraG was incorporated into G. lamblia DNA in a time-dependent manner at a ratio of 1 araG for each 27 2'-deoxyguanosine residues. Short-term exposure of growing cultures to araG was inhibitory to DNA synthesis but not to RNA or protein synthesis. Over an extended period, synthesis of all three macromolecules was depressed. Attempts to measure araG phosphorylation by cell-free extracts of G. lamblia under a variety of nucleoside kinase and nucleoside phosphotransferase assay conditions were unsuccessful. In an attempt to understand further the action of araG, the metabolic pathways of guanine, guanosine and 2'-deoxyguanosine were delineated in detail. The presence of araG did not appear to cause any major alterations in the metabolism of these compounds; however, it was accompanied by a 3- to 4-fold increase in the endogenous pools of ATP and GTP.

Adenine↗
PubMed1987

Captopril versus placebo in congestive heart failure: effects on oxygen delivery to exercising skeletal muscle.

The effects of captopril versus placebo on oxygen consumption in the exercising leg have been examined using Doppler measurements of femoral flow and arteriovenous oxygen difference. Twenty patients with heart failure were randomized to captopril 25 mg (N = 10) or placebo (N = 10). Maximal supine exercise of one leg was performed before treatment and again 1 h and 4 h afterwards. Systemic haemodynamic variables were unaffected by placebo, but captopril increased stroke index at peak exercise from 26 +/- 3 to 34 +/- 3 ml beat-1 m-2 and reduced pulmonary artery wedge pressure from 26 +/- 3 to 16 +/- 3 mmHg (P less than 0.05). Despite the captopril-induced improvement in left ventricular function, exercise duration did not increase significantly and peak values for femoral flow (1059 +/- 178 to 938 +/- 134 ml min-1, P = NS), and oxygen consumption (134 +/- 26 to 111 +/- 18 ml min-1, P = NS) in the exercising leg were unaffected. Cutaneous flow, as reflected by skin temperature (27.5 +/- 0.4 to 27.6 +/- 0.4 degrees C, P = NS), was also unaffected. In the patients randomized to captopril, the acute improvement in left ventricular function was abbreviated and, after 4 h, all variables had returned towards baseline. Moreover, when the invasive studies were repeated after four weeks chronic treatment responsiveness to converting enzyme inhibition had attenuated and there were no detectable differences between the captopril and placebo groups. These data have demonstrated an acute captopril-induced improvement in left ventricular function in patients with congestive heart failure. Nevertheless the beneficial acute response was abbreviated predicting the development of early tolerance. Oxygen delivery to the exercising leg showed no tendency to increase either acutely when left ventricular function was significantly improved, or chronically when systemic responsiveness had attenuated. Thus irrespective of its effects on left ventricular function, captopril does not increase nutritive flow to exercising skeletal muscle in congestive heart failure.

Captopril↗
PubMed1987

The effects of early coronary patency on the evolution of myocardial infarction: a prospective arteriographic study.

The effects of early spontaneous coronary patency on the evolution of myocardial infarction were evaluated in 41 patients. They had coronary arteriography (mean (SEM)) 3.1 (0.2) hours after the onset of chest pain with repeat studies 90 minutes and three days later. In 12 (29%) patients the infarct related coronary artery was patent at the first arteriogram (group 1). A further 10 patients, nine of whom received thrombolytic treatment, showed early recanalisation of the infarct related coronary artery within 90 minutes of treatment (group 2). In the remainder the infarct related coronary artery was persistently occluded (group 3). Baseline values for infarct location, the sum of ST elevation in all leads, QRS scores, and serum creatine kinase activity did not permit discrimination between the groups. Nevertheless, patterns of ST segment change and enzyme release in group 1 were closely similar to those that occurred in response to thrombolysis in group 2. Thus compared with group 3, groups 1 and 2 showed earlier 50% reduction in the sum of peak ST elevation in all leads and earlier peaking of serum creatine kinase activity. Importantly, creatine kinase release was significantly attenuated in group 1, rising to a peak serum activity (mean (SEM)) of only 1242 (415) IU/1. Analysis of angiographic left ventricular ejection fractions at three days indicated limitation of infarct size in groups 1 and 2 compared with group 3. Mean (SEM) ejection fraction, however, was best preserved in group 1 (62(6)%) and in this group the frequency of non-Q wave infarction was higher than in groups 2 and 3. Thus in patients who present with a patent infarct related coronary artery early during infarction: (a) there is a reduction in the pattern of infarct size as reflected by attenuation of release of creatine kinase, preservation of left ventricular ejection fraction, and a relatively high frequency of non-Q wave infarction; (b) patterns of ST segment change and creatine kinase release resemble those that occur after successful thrombolytic treatment, suggesting that early coronary patency is the result of spontaneous recanalisation of a previously occluded artery.

Adult↗
PubMed1986

EPR studies show that all lanthanides do not have the same order of binding to calmodulin.

Calmodulin, spin labeled at Tyr-99, has been titrated with the lanthanides La3+, Nd3+, Eu3+, Tb3+, Er3+ and Lu3+ as well as Ca2+ and Cd2+. The titration was monitored by EPR and changes in mobility of the spin label, due to binding into the labeled site and protein conformational change, were observed. Comparison of these titration curves with theoretical binding curves for the various calmodulin-metal species, show that different lanthanides have different high affinity sites. Three basic categories were observed, with Lu3+ and Er3+ behaving like Ca2+, Eu3+ and Tb3+ binding in the opposite order from Ca2+, and La3+ and Nd3+ different from either Ca2+ or Tb3+.

Calcium↗
PubMed1986

A flow-dialysis method for obtaining relative measures of association constants in calmodulin-metal-ion systems.

A flow-dialysis apparatus suitable for the study of high-affinity metal-binding proteins has been utilized to study calmodulin-metal exchange as a measure of relative calmodulin-metal association constants. Calmodulin labelled with radioactive 153Gd was dialysed against buffer containing various competing metal ions. The rate of label exchange was monitored by a gamma-ray scintillation detector. Competing metals used were Ca2+ and Cd2+, and the lanthanides Gd3+, Eu3+, La3+ and Lu3+. All exchange processes were first-order, and two categories of metal were found: Ca2+ and Cd2+ in one, the lanthanides comprising the other. In addition calmodulin-metal complexes with radioactive 109Cd and 45Ca released the bound label without any competing metal being added to the buffer. The kinetics of this metal loss can be described by two consecutive first-order processes, and the fraction of label associated with each rate can be determined. Studies of phosphodiesterase activation by calmodulin show Cd2+ and calmodulin to cause 80% of the maximum activation found when Ca2+ and calmodulin are used.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1986

Solvent interactions with N, N-dialkylnicotinamides and their effects on rotational barriers.

Carbon-13 nuclear magnetic resonance techniques were employed to examine the effects of solvent environment on rotational barriers in a series of molecules structurally-related to the analeptic, nikethamide: N,N-dimethylnicotinamide, N,N-di-n-propylnicotinamide, and 1-nicotinoyl piperidine. Total bandshape analysis was performed for the exchanging alkyl carbon resonances of these compounds as a function of temperature in four solvent systems: D2O, CH3OD, CH3CH2OD and CDCl3. The rate constants for rotation about the amide bond obtained in this way were used to calculate free energy (delta G), enthalpy (delta H) and entropy (delta S) of activation parameters for this process. Our results indicate that rotational barriers are less affected by the nature of the alkyl chain attached to the amide nitrogen than by the size and polarity of the solvent molecules. Interpretation of the thermodynamic parameters in light of both nikethamide analogue structure and solvent type has further clarified the manner in which hydrogen bonding interactions between solvent molecules and the carbonyl oxygen of these analogues stabilize transition state conformers.

Hydrogen Bonding↗