PubMed Health⌕ Search

Biomedical subjects

A W Simpson

Publications and source records attributed to A W Simpson.

At least 37 records · Page 2Linked to original sources
PubMed1990

The effects of siguazodan, a selective phosphodiesterase inhibitor, on human platelet function.

1. The effects of siguazodan (SK&F 94836) a selective phosphodiesterase (PDE) inhibitor with inotropic and vasodilator activity, were studied on human platelets. 2. Siguazodan selectively inhibited the major cyclic AMP-hydrolysing PDE in human platelet supernatants. The inhibited enzyme has been variously termed cyclic GMP-inhibited PDE or PDE-III. 3. In platelet-rich plasma (PRP), siguazodan inhibited U46619-induced aggregation more potently than that induced by ADP and collagen. Treatment of the PRP with aspirin had no effect on the potency of siguazodan. 4. In washed platelets, siguazodan increased cyclic AMP levels and reduced cytoplasmic free calcium [( Ca2+]i). ADP decreased the ability of siguazodan to raise cyclic AMP and this may explain its lower potency in inhibiting responses to ADP. 5. Siguazodan has anti-platelet actions over the same concentration range that it is an inotrope and vasodilator.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1990

Assessment of fetal-maternal haemorrhage in mothers with hereditary persistence of fetal haemoglobin.

Kleihauer examination of peripheral blood cannot be used reliably to detect transplacental fetal-maternal haemorrhage in mothers with hereditary persistence of fetal haemoglobin (HPFH). In Rh(D) negative pregnancies diagnostic confusion with a large fetal-maternal haemorrhage could result in the administration of inappropriately excessive amounts of anti-D immunoglobulin, and the inability to diagnose and quantify transplacental haemorrhage in maternal HPFH by current methods could result in insufficient anti-D administration and subsequent Rh(D) sensitisation. Accordingly, a method to detect and quantify fetal-Rh(D) positive maternal haemorrhage using erythrocyte fluorescent immunocytometry was developed. An indirect immunofluorescence method with IgG anti-D immunoglobulin as the primary antibody was used, combined with quantitative analysis on a fluorescence activated cell sorter. The method was accurate, specific, and sensitive and could detect a contaminating population of 0.1% Rh(D) positive cells in Rh(D) negative blood--a level of fetal-maternal haemorrhage well covered by a single dose of 500 IU of anti-D immunoglobulin.

Adult↗
PubMed1989

Free calcium rise and mitogenesis in glial cells caused by endothelin.

The peptide endothelin causes a biphasic rise in intracellular free calcium levels in cultured Type-1 astrocytes and C6 glioma cells, suggesting that glial cells may be the physiological target of endothelin in the brain. Endothelin also causes a calcium-dependent increase [3H]thymidine incorporation in primary cultures of rat cerebellum, indicating that, among other possible roles, this peptide may mediate mitogenesis in brain.

Animals↗
PubMed1989

Endothelin evoked Ca2+ transients and oscillations in A10 vascular smooth muscle cells.

Endothelin (200 nM) evoked a rapid rise in [Ca2+]i which was then followed by a maintained elevation of [Ca2+]i. The initial transient can be explained by the release of stored Ca2+ whilst the maintained plateau is likely to be an influx of Ca2+ as it was partially inhibited by nifedipine (5 microM) and the remaining component abolished by the removal of extracellular Ca2+. Vasopressin (1 nM) evoked a similar response which also showed a nifedipine insensitive component to it's plateau phase. Endothelin also evoked oscillations in [Ca2+]i; these where characterised by a rapid rising phase followed by a slower decline, with no 'pacemaker' rise in [Ca2+]i preceding the rising phase. The oscillations were inhibited by the addition of 5 microM nifedipine or the removal of extracellular Ca2+ suggesting they are at least in part dependent on voltage gated Ca2+ entry.

Animals↗
PubMed1989

Free calcium at rest during "catch" in single smooth muscle cells.

Tension and intracellular free calcium concentration [( Ca2+]i) were measured simultaneously in single smooth muscle cells isolated from the anterior byssus retractor muscle (ABRM) of Mytilus edulis that were loaded with the fluorescent Ca2+ indicator fura-2. Electrical stimulation evoked a transient elevation of [Ca2+]i associated with a "catch" contraction. During the catch state, however, [Ca2+]i was effectively at its resting level and was unaffected by 5-hydroxytryptamine, which induced a rapid relaxation from catch. The results indicate that a maintained high [Ca2+]i is not required for the maintenance of catch tension in intact ABRM and that there was no significant change in [Ca2+]i upon abolition of catch.

Animals↗
PubMed1989

Effects of 5-hydroxytryptamine (serotonin) and forskolin on intracellular free calcium in isolated and fura-2 loaded smooth-muscle cells from the anterior byssus retractor (catch) muscle of Mytilus edulis.

Effects of 5-hydroxytryptamine (5-HT) and forskolin on intracellular free calcium concentration [( Ca2+]i) were studied in suspensions of fura-2 loaded smooth-muscle cells from the anterior byssus retractor 'catch' muscle of Mytilus edulis. The successive addition of 5 mM carbachol (CCh) and 100 mM KCl to the suspension evoked a transient elevation of [Ca2+]i from the resting value of 124 +/- 2.7 nM (mean +/- SE, n = 18) to 300-400 nM, which was associated with contraction. The change in [Ca2+]i induced CCh was concentration-dependent with the EC50 of 10(-5) M. The resting [Ca2+]i was unaffected by 10 microM 5-HT. The change in [Ca2+]i induced by 5 mM CCh was suppressed by 5-HT from 167 +/- 14.0 (n = 11) to 124 +/- 14.9 (n = 8) nM whereas that induced by 100 mM KCl was enhanced from 321 +/- 31.9 to 405 +/- 17.6 nM (n = 8). 5-HT applied during the decaying phase of the CCh response caused a rapid decline in [Ca2+]i. In both the responses to CCh and KCl, the falling phase was accelerated by 5-HT. 10 microM forskolin, a potent activator of adenylate cyclase, mimicked the effects of 5-HT as did a membrane-permeant cyclic AMP analogue, 8-parachlorophenylthio cyclic AMP (cpt-cAMP). Application of 100 microM cpt-cAMP partially suppressed the Ca2+i response to CCh and enhanced that to KCl. D-Tubocurarine (500 microM) added during the decaying phase of the response induced by 100 microM CCh, caused a rapid decline in [Ca2+]i similar to that caused by both 5-HT and forskolin.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Spontaneous oscillations and agonist-evoked changes in Ca2+ in cultured smooth muscle cells.

In confluent A10 aortic smooth muscle cells, at 37 degrees C and in the presence of 1 mM extracellular Ca2+ ([Ca2+]o), the resting intracellular free calcium [Ca2+]i) was found to be 111 +/- 6 nM (n = 17), and in single cells it was 82.4 +/- 7.6 nM. In the presence of 1 mM EGTA, in confluent cells, resting [Ca2+]i was 88.1 +/- 11 nM. The confluent cells showed spontaneous transients and elevations in [( Ca2+]i) as well as maintained oscillations. The oscillations had a periodicity of 6-9 s and were not present in single cells. One nanomolar and 2 microM vasopressin elevated [Ca2+]i to between 0.7 and 3 microM. In the presence of extracellular Ca2+, the initial transient was followed by a plateau phase that declined slowly; in EGTA, this plateau phase was not present but could be restored by adding back Ca2+. Although A10 cells show spontaneous action potentials, oscillations in [Ca2+]i have not been reported. The plateau phase of the vasopressin response appears to be mediated by Ca2+ influx, whereas the initial transient is consistent with the release of stored Ca2+.

Arginine Vasopressin↗
PubMed1988

Carbachol and KCl-induced changes in intracellular free calcium concentration in isolated, fura-2 loaded smooth-muscle cells from the anterior byssus retractor muscle of Mytilus edulis.

Intracellular free calcium concentration [( Ca2+]1) was measured in suspensions of fura-2 loaded smooth-muscle cells isolated from the anterior byssus retractor muscle of Mytilus edulis. Successive application of 5mM carbachol (CCh) and 100mM KCl to the cells transiently elevated [Ca2+]1 from the resting value of 124 +/- 4.5nM (mean +/- S.E., n = 14) to 295 +/- 15.3 and 383 +/- 20.5 nM, respectively. The response to CCh was concentration-dependent with an ED50 of 10(-5) M. Under the microscope, 67 +/- 3.0 and 83 +/- 1.3 % of fura-2 loaded cells contracted on the addition of 5mM CCh and 100mM KCl, respectively. In Ca2+ -free sea water, the CCh induced change in [Ca2+]1 was partially suppressed whereas that induced by KCl was completely abolished, suggesting an agonist-evoked release of stored Ca2+.

Animals↗
PubMed1988

Effects of SK&F 94120, an inhibitor of cyclic nucleotide phosphodiesterase type III, on human platelets.

Elevation of cyclic AMP concentrations in platelets inhibits agonist-induced responses. Pharmacological interventions which could increase the levels of platelet cyclic AMP include activation of the synthesis of cyclic AMP or inhibition of its breakdown. In this study we have investigated the effects of SK&F 94120 on human platelet phosphodiesterase (PDE) activities separated by ion-exchange chromatography, and studied the effects of this agent on platelet responses caused by the agonists collagen, U44069 and ADP. Four PDE activities were identified from human platelet preparations. The PDE activities found comprised a cyclic GMP selective PDE, a Ca2+/calmodulin stimulated PDE, a cyclic GMP stimulated PDE and a "low Km" PDE activity called PDE III by analogy with activities described in other tissues. SK&F 94120 was found selectively to inhibit the "low Km" PDE III activity with an IC50 of 10.8 microM, which is consistent with the effects of this compound on cardiac ventricle PDE activities. Exposure of human platelets to SK&F 94120 produced concentration dependent increases in cyclic AMP, showing that inhibition of PDE III activity alone can cause an increase in the level of platelet cyclic AMP. SK&F 94120 also caused an inhibition of platelet responses to collagen, U44069 and ADP. However, SK&F 94120 was much less effective as an inhibitor of aggregation induced by ADP (IC50 greater than 100 microM) than by collagen (IC50 = 24.1 microM) or by U44069 (IC50 = 1.7 microM). Isobutylmethylxanthine (IBMX), a non-selective PDE inhibitor, was less effective than SK&F 94120 as an inhibitor of platelet responses for the same measured increase in cyclic AMP levels. M&B 22948 and rolipram, inhibitors of PDE I and PDE IV respectively, had no significant effect on platelet responses. These data suggest that selective inhibition of PDE III is the primary mechanism of action of SK&F 94120 as an inhibitor of agonist-induced platelet responses, and that increased cyclic AMP in the pool controlled by PDE III has important consequences on platelet responses. Moreover, these data suggest that some form of compartmentalization of cyclic AMP and/or PDE activity exists in human platelets.

1-Methyl-3-isobutylxanthine↗
PubMed1987

Elevation of pHi is not an essential step in calcium mobilisation in fura-2-loaded human platelets.

Human platelets were co-loaded with the fluorescent indicators BCECF and fura-2 to measure pHi and [Ca2+]i and incubated with aspirin to block cyclooxygenase. Either pHi and shape change and aggregation or pHi and [Ca2+]i were measured simultaneously in the same stirred cuvette, at 37 degrees C. In Hepes-buffered saline containing 1 mM Ca2+, mean resting pHi was 6.98 +/- 0.01 (SE, n = 59). Changes of pHi up to +/- 0.35 units, imposed by additions of NH4Cl, CO2 or nigericin, produced no shape change or aggregation and only insignificant changes in [Ca2+]i. Sufficient thrombin to raise [Ca2+]i over 1 microM and cause rapid shape change and aggregation increased pHi by no more than 0.05 units, and the increase in pHi lagged behind the elevation of [Ca2+]i. We conclude that changes in pHi do not form a necessary or sufficient component of the pathways leading to receptor-mediated Ca2+ mobilisation or the stimulation of shape change or aggregation.

Benzofurans↗
PubMed1987

Composition of immune complexes and their relation to plasma fibronectin in chronic myeloproliferative disorders.

High concentrations of circulating immune complexes were detected by polyethylene glycol precipitation in 11 of 20 patients with myelofibrosis secondary to chronic myeloproliferative disease. Circulating immune complexes showed a positive correlation with plasma IgG concentrations both in patients and controls. Covariance analysis of the two groups showed significantly increased polyethylene glycol precipitable IgG in patients when adjusted for plasma IgG concentrations, indicating that the patients had significantly increased concentrations of complexed IgG. The immune complexes contained IgG, C3, and fibronectin and were inversely correlated with plasma fibronectin concentrations, suggesting that this major non-specific opsonin is important for the normal clearance of immune complexes. Therapeutic plasmapheresis efficiently removed circulating complexes and produced an increase in plasma fibronectin. This suggests that plasmapheresis may be useful for controlling immune complex mediated complications of these disorders.

Aged↗
PubMed1986

Low concentrations of the stable prostaglandin endoperoxide U44069 stimulate shape change in quin2-loaded platelets without a measurable increase in [Ca2+]i.

Dose-response relationships for raised cytoplasmic free calcium concentration, [Ca2+]i, and shape change were measured simultaneously in quin2-loaded human platelets. With the calcium ionophore ionomycin the threshold [Ca2+]i for shape change was 300 nM with a maximal response at 800 nM. With 1 mM external Ca2+ the U44069 concentrations required to stimulate half-maximal shape change and an increase in [Ca2+]i were 2 and 41 nM, respectively. For PAF these values were 8.7 and 164 pg/ml, respectively. Low concentrations of U44069 and PAF evoked substantial shape change without any rise in [Ca2+]i. In the absence of external Ca2+, U44069 stimulated half-maximal shape change at 2 nM, and half-maximal elevation of [Ca2+]i at 69 nM: here, increased [Ca2+]i never reached the threshold [Ca2+]i for shape-change derived with ionomycin. These results suggest that some transduction mechanism other than elevated [Ca2+]i, as yet unidentified, can cause shape change.

Aminoquinolines↗
PubMed1984

TMB-8 inhibits secretion evoked by phorbol ester at basal cytoplasmic free calcium in quin2-loaded platelets much more effectively than it inhibits thrombin-induced calcium mobilisation.

TMB-8 is widely regarded as an 'intracellular calcium antagonist', supposedly inhibiting the mobilisation of intracellular calcium. Rarely, however, have the effects of this compound on Ca2+ movements been measured. We report here that TMB-8 is not very effective in inhibiting thrombin-induced Ca2+ influx or internal release in human platelets judged from the fluorescent signal of cytoplasmic quin2. Only approx. 40% inhibition was seen at 500 microns TMB-8. Somewhat lower concentrations blocked the secretory response to thrombin and also the secretion evoked at basal [Ca2+]i by phorbol ester and collagen. It is suggested that one target for TMB-8 may be the C-kinase pathway.

Aminoquinolines↗
PubMed1984

The biochemical and functional heterogeneity of circulating human plasma fibronectin.

Human plasma fibronectin purified by affinity chromatography, consisted of homogeneous 215 kD protein subunits when assessed by SDS polyacrylamide gel electrophoresis. On isoelectric focusing however, 5 separate fractions were present, with isoelectric points ranging from 5.6 to 6.1. Isoelectric focusing and immunofixation of native plasma produced similar but not identical appearances. Only 15% of the total plasma fibronectin opsonically stimulated the ingestion of Saccharomyces cerevisiae by human peripheral blood monocytes, and this opsonic fibronectin was confined to the fraction with an isoelectric point of 6.1.

Electrophoresis, Polyacrylamide Gel↗