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Biomedical subjects

S C Taylor

Publications and source records attributed to S C Taylor.

At least 19 recordsLinked to original sources
PubMed2004

Infection with an avirulent phoP mutant of Neisseria meningitidis confers broad cross-reactive immunity.

Successful vaccines against serogroup A and C meningococcal strains have been developed, but current serogroup B vaccines provide protection against only a limited range of strains. The ideal meningococcal vaccine would provide cross-reactive immunity against the variety of strains that may be encountered in any community, but it is unclear whether the meningococcus possesses immune targets that have the necessary level of cross-reactivity. We have generated a phoP mutant of the meningococcus by allele exchange. PhoP is a component of a two-component regulatory system which in other bacteria is an important regulator of virulence gene expression. Inactivation of the PhoP-PhoQ system in Salmonella leads to avirulence, and phoP mutants have been shown to confer protection against virulent challenge. These mutants have been examined as potential live attenuated vaccines. We here show that a phoP mutant of the meningococcus is avirulent in a mouse model of infection. Moreover, infection of mice with the phoP mutant stimulated a bactericidal immune response that not only killed the infecting strain but also showed cross-reactive bactericidal activity against a range of strains with different serogroup, serotype, and serosubtyping antigens. Sera from the mutant-infected mice contained immunoglobulin G that bound to the surface of a range of meningococcal strains and mediated opsonophagocytosis of meningococci by human phagocytic cells. The meningococcal phoP mutant is thus a candidate live, attenuated vaccine strain and may also be used to identify cross-reactive protective antigens in the meningococcus.

Animals↗
PubMed2004

Preparing for the MFAEM examination.

The MFAEM may take over as the primary membership examination for progression to higher professional training in Emergency Medicine. As a relatively young examination it still suffers from a lack of associated study material and a formal syllabus. The emergence of a specific membership examination such as MFAEM represents the growth in stature of A&E as a speciality in its own right. As the examination becomes more popular and growing numbers of doctors apply there will be a similar expansion of study material and available resources. MRCSEd(A&E) remains a solid alternative and eligibility for this examination is similar to MFAEM part B. However, success at a relevant part one is required before sitting this. The MFAEM part A is more balanced and relevant primary examination for A&E trainees but if one is interested in dual accreditation or has a specific interest in another speciality then sitting the MRCP, MRCS or FRCA may be more appropriate before approaching the MFAEM part B or MRCSEd(A&E).

Accidents↗
PubMed2003

Hypoparathyroidism and 22q11 deletion syndrome.

AIMS: To investigate a population of individuals with 22q11 deletion syndrome for hypocalcaemia. METHODS: A detailed clinical history enquiring into symptoms of hypocalcaemia and blood sampling to assess for hypocalcaemia and hypoparathyroidism, of patients outside the neonatal period known to have the 22q11 microdeletion from fluorescent in situ hybridisation studies was taken. RESULTS: Sixty one individuals were identified, of whom 23 were untraceable and one was unable to give informed consent. Biochemical investigations were performed on 27 subjects. Ten subjects had review of notes only. Four subjects had previously identified hypoparathyroidism. A new case of hypoparathyroidism was identified. Three subjects had borderline hypocalcaemia. DISCUSSION: In this population of patients with 22q11 deletion syndrome, 13% of the total or 30% of those biochemically assessed had evidence of reduced serum calcium concentrations. It is likely that 13-30% of patients with 22q11 deletion syndrome have possible hypoparathyroidism outside the neonatal period. Reported symptoms of hypocalcaemia did not correlate with biochemical evidence of persisting hypocalcaemia. We have shown that previously undiagnosed asymptomatic hypoparathyroidism occurs in patients with 22q11 deletion syndrome and conclude that screening of this population should be considered.

Adolescent↗
PubMed2001

Differential coupling of voltage-gated Ca(2+) channels to catecholamine secretion from separate PC12 cell batches.

Amperometric recordings were employed to investigate the coupling of Ca(2+) channels to catecholamine secretion in two batches of pheochromocytoma (PC12) cells. In 'new' (freshly obtained) cells (PC12n cells), secretion was dependent on Ca(2+) influx through L-type and N-type Ca(2+) channels. By contrast, in 'aged' cells (maintained in liquid nitrogen for 6-8 years; PC12a cells), secretion was mostly dependent on Ca(2+) influx through N-type channels. Patch clamp recordings revealed that L-type channels accounted for only ca. 26% of total whole-cell current in PC12a cells (determined by blockade caused by 2 microM nifedipine). In contrast, nifedipine suppressed currents by ca. 59% in PC12n cells. Thus important differences in fundamental physiological properties can be observed in PC12 cell batches even when obtained from the same source and maintained under identical conditions.

Animals↗
PubMed2001

Prion protein fragment 106-126 potentiates catecholamine secretion from PC-12 cells.

The toxic actions of scrapie prion protein (PrP(sc)) are poorly understood. We investigated the ability of the toxic PrP(sc) fragment 106-126 to interfere with evoked catecholamine secretion from PC-12 cells. Prion protein fragment 106-126 (PrP106-126) caused a time- and concentration-dependent augmentation of exocytosis due to the emergence of a Ca(2+) influx pathway resistant to Cd(2+) but sensitive to other inorganic cations. In control cells, secretion was dependent on Ca(2+) influx through L- and N-type Ca(2+) channels, but after exposure to PrP106-126, secretion was unaffected by N-type channel blockade. Instead, selective L-type channel blockade was as effective as Cd(2+) in suppressing secretion. Patch-clamp recordings revealed no change in total Ca(2+) current density in PrP106-126-treated cells or in the contribution to total current of L-type channels, but a small Cd(2+)-resistant current was found only in PrP106-126-treated cells. Thus PrP106-126 augments secretion by inducing a Cd(2+)-resistant Ca(2+) influx pathway and alters coupling of native Ca(2+) channels to exocytosis. These effects are likely contributory factors in the toxic cellular actions of PrP(sc).

Animals↗
PubMed2001

Malignant melanoma in African Americans.

Although rare, malignant melanoma (MM) is a real and serious risk for African Americans. African Americans have a proportionately higher incidence of acral melanoma, both the acral lentiginous melanoma (ALM) histologic subtype and subungual melanoma (SM). MM is more likely to be diagnosed at a later stage in African Americans and carries a worse prognosis. Given these facts, the relatively simple and inexpensive primary and secondary preventions for MM should be standard, particularly in the African American patient.

Black or African American↗
PubMed2000

Protein kinase C evokes quantal catecholamine release from PC12 cells via activation of L-type Ca2+ channels.

Application of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) to PC12 cells under resting conditions evoked quantal catecholamine secretion, as detected amperometrically. This effect was not mimicked by 4alpha-phorbol-12,13-didecanoate, another phorbol ester, which is inactive with respect to protein kinase C activation, and was prevented by the protein kinase C inhibitor bisindolylmaleimide. TPA also caused a rise of [Ca(2+)](i) in Fura-2-loaded PC12 cells, and again this was not mimicked by 4alpha-phorbol-12,13-didecanoate and could be blocked by bisindolylmaleimide. TPA-evoked secretion was entirely dependent on extracellular Ca(2+) and was fully abolished by nifedipine, as were TPA-induced rises of [Ca(2+)](i). Resting membrane potential, monitored using perforated patch recordings, was unaffected by TPA. However, a small (6-8 mV) hyperpolarizing shift in the voltage dependence of Ca(2+) channel currents (determined using whole-cell patch clamp recordings) was induced by TPA, and this could be fully prevented by nifedipine. In contrast to results with depolarizing stimuli, which evoke exocytosis because of Ca(2+) influx through N-type channels in these cells, the present results indicate that protein kinase C activation leads directly to quantal catecholamine secretion in the absence of depolarizing stimuli via a selective shift in the activation of L-type Ca(2+) channels.

Animals↗
PubMed2000

Mitochondrial inhibitors evoke catecholamine release from pheochromocytoma cells.

Quantal catecholamine secretion evoked from individual pheochromocytoma (PC12) cells by exposure to mitochondrial inhibitors and uncouplers was monitored in real time using amperometry. Cyanide (0.05-5 mM) caused a concentration-dependent increase in the frequency of amperometric events. This secretory response was abolished by removal of extracellular Ca(2+) and by the application of Cd(2+) (200 microM), a nonselective blocker of voltage-gated Ca(2+) channels. Secretion was also inhibited by ca. 75% following pretreatment of cells with omega-conotoxin GVIA to inhibit N-type Ca(2+) channels selectively. Secretion was also detected when cells were exposed to rotenone (10 microM), dinitrophenol (250 microM) and p-trifluoromethoxyphenyl hydrazone (1 microM) and, as for cyanide, these secretory responses were abolished by removal of extracellular Ca(2+) or application of 200 microM Cd(2+). These results indicate that, like hypoxia, mitochondrial inhibitors and uncouplers evoke catecholamine secretion from PC12 cells which is wholly dependent on Ca(2+) influx through voltage-gated Ca(2+) channels.

2,4-Dinitrophenol↗
PubMed2000

Three distinct Ca(2+) influx pathways couple acetylcholine receptor activation to catecholamine secretion from PC12 cells.

Amperometry and microfluorimetry were employed to investigate the Ca(2+)-dependence of catecholamine release induced from PC12 cells by cholinergic agonists. Nicotine-evoked exocytosis was entirely dependent on extracellular Ca(2+) but was only partly blocked by Cd(2+), a nonselective blocker of voltage-gated Ca(2+) channels. Secretion and rises of [Ca(2+)](i) observed in response to nicotine could be almost completely blocked by methyllycaconitine and alpha-bungarotoxin, indicating that such release was mediated by receptors composed of alpha7 nicotinic acetylcholine receptor subunits. Secretion and [Ca(2+)](i) rises could also be fully blocked by co-application of Cd(2+) and Zn(2+). Release evoked by muscarine was also fully dependent on extracellular Ca(2+). Muscarinic receptor activation stimulated release of Ca(2+) from a caffeine-sensitive intracellular store, and release from this store induced capacitative Ca(2+) entry that could be blocked by La(3+) and Zn(2+). This Ca(2+) entry pathway mediated all secretion evoked by muscarine. Thus, activation of acetylcholine receptors stimulated rises of [Ca(2+)](i) and exocytosis via Ca(2+) influx through voltage-gated Ca(2+) channels, alpha7 subunit-containing nicotinic acetylcholine receptors, and channels underlying capacitative Ca(2+) entry.

Animals↗
PubMed1999

Hypoxic enhancement of quantal catecholamine secretion. Evidence for the involvement of amyloid beta-peptides.

Prolonged exposure to hypoxia (10% O(2)) enhanced quantal catecholamine release evoked from O(2)-sensing pheochromocytoma (PC12) cells, as monitored using single-cell amperometric recordings. The enhancement of exocytosis was apparent after 12 h of hypoxia and was maximal at 24 h. Elevated levels of secretion were due to the emergence of a Ca(2+) influx pathway that persisted during complete blockade of known voltage-gated Ca(2+) channels. Secretion triggered by this Ca(2+) influx was severely reduced by known inhibitors of Alzheimer's amyloid beta-peptides (AbetaPs), including an N terminus-directed monoclonal antibody. The enhancing effect on secretion of chronic hypoxia was mimicked closely by direct application of AbetaP to cells under normoxic conditions, although the effects of AbetaP were more rapid at onset, being maximal after only 6 h. The present results suggest that prolonged hypoxia can induce formation of Ca(2+)-permeable AbetaP channels and that such induction can lead directly to excessive neurosecretion. This is a potential contributory factor to AbetaP pathophysiology following cerebral ischemia.

Alzheimer Disease↗
PubMed1999

Acid-evoked quantal catecholamine secretion from rat phaeochromocytoma cells and its interaction with hypoxia-evoked secretion.

1. Amperometric recordings using polarized carbon fibre microelectrodes were used to detect exocytosis of catecholamines from rat phaeochromocytoma (PC12) cells in response to a reduction in pHo. 2. Exocytosis was detected at pHo levels of between 7.2 and 6.8. This was probably due to intracellular acidification, since acid-evoked secretion was enhanced by the Na+-H+ exchange blocker ethylisopropylamiloride (30 microM), and was mimicked by sodium propionate (10 mM), which causes selective intracellular acidosis. 3. Acid-evoked exocytosis was abolished by removal of Ca2+o or application of 200 microM Cd2+. It was unaffected by nifedipine, but significantly reduced by either omega-conotoxin GVIA (1 microM) or omega-agatoxin GIVA (200 nM). The two toxins applied together almost completely abolished (> 97 %) acid-evoked secretion. 4. Hypoxia-evoked catecholamine release was potentiated under acidic conditions and suppressed under alkaline conditions in a manner which indicated a greater than additive interaction of these two stimuli. 5. Our results indicate that, like carotid body arterial chemoreceptors, PC12 cells represent model chemoreceptor cells for both hypoxia and acidity and that the release of catecholamines in response to these physiological stimuli is dependent on Ca2+ influx through voltage-gated N- and P/Q-type Ca2+ channels.

Animals↗
PubMed1999

Potentiation of quantal catecholamine secretion by glibenclamide: evidence for a novel role of sulphonylurea receptors in regulating the Ca(2+) sensitivity of exocytosis.

Electrochemical detection of quantal catecholamine release from PC-12 cells revealed that glibenclamide, an inhibitor of ATP-sensitive K(+) channels, potentiated Ca(2+)-dependent exocytosis evoked by raised extracellular [K(+)] and by exposure of cells to caffeine. Glibenclamide was without effect on voltage-gated Ca(2+) currents, membrane potential, or rises of [Ca(2+)](i) evoked by either raised extracellular [K(+)] or caffeine. The dependence of K(+)-evoked secretion on extracellular Ca(2+) was shifted leftward in the presence of glibenclamide, with a small increase in the plateau level of release, suggesting that glibenclamide primarily increased the Ca(2+) sensitivity of the exocytotic apparatus. Enhancement of secretion by glibenclamide was reversed by pinacidil and cromakalim, indicating that the effects of glibenclamide were mediated via an action on a sulfonylurea receptor. These results demonstrate that sulfonylurea receptors can modulate Ca(2+)-dependent exocytosis via a mechanism downstream of Ca(2+) influx or mobilization.

ATP-Binding Cassette Transporters↗
PubMed1999

Chronic hypoxia enhances the secretory response of rat phaeochromocytoma cells to acute hypoxia.

1. Amperometric recordings were made from individual phaeochromocytoma (PC12) cells using carbon fibre microelectrodes to investigate the effects of chronic hypoxia (10% O2) on the secretory responses evoked by acute hypoxia. 2. Exposure to chronic hypoxia for 21-26 h increased the frequency of exocytotic events evoked in response to acute hypoxia (PO2 ca 10-60 mmHg). 3. Chronic hypoxia increased the value of Q1/3, determined by the integration of amperometric events, indicating an increase in quantal size: this reflects either an increase in vesicular dimensions or vesicular catecholamine concentration. 4. Exocytotic frequency evoked by bath application of tetraethylammonium (1-10 mM) was significantly enhanced following chronic hypoxia. 5. In both control and chronically hypoxic PC12 cells, exocytosis in response to acute hypoxia was completely abolished in Ca2+-free solutions. Cd2+ (200 microM) completely inhibited exocytosis from control cells, but left a significant residual release in chronically hypoxic PC12 cells. 6. The Cd2+-resistant release evoked by acute hypoxia in chronically hypoxic PC12 cells was inhibited by inorganic ions (0.01-10 mM) in a potency order of La3+ > Gd3+ > Zn2+. Ni2+ (10 mM) was without effect. 7. Our results suggest that chronic hypoxia enhances the secretory response of PC12 cells in part by increasing the depolarization mediated by an oxygen-sensitive K+ channel. In addition, acute hypoxia activates a Cd2+-resistant Ca2+ influx pathway in chronically hypoxic PC12 cells.

Adrenal Gland Neoplasms↗
PubMed1999

Analysis of a translational enhancer present within the 5'-terminal sequence of the genomic RNA of potato virus S.

When present as a transcript leader the 5' untranslated sequence from the potato virus S genomic RNA molecule enhances translation of a downstream open reading frame both in vitro and in vivo. Translational enhancement was 30-fold in rabbit reticulocyte lysate and 15 fold in wheat germ above translation from a transcript with a synthetic leader. Transient expression experiments using tobacco protoplasts and particle bombardment of leaf tissue resulted in enhancement of fourteen and five-fold, respectively, above translation with a synthetic leader. In stably transformed plants the PVS 5'UTR enhanced translation yield ca. 5-fold compared with a synthetic 5'UTR.

5' Untranslated Regions↗
PubMed1999

Store-operated Ca2+ influx and voltage-gated Ca2+ channels coupled to exocytosis in pheochromocytoma (PC12) cells.

Microamperometry was used to monitor quantal catecholamine release from individual PC12 cells in response to raised extracellular K+ and caffeine. K+-evoked exocytosis was entirely dependent on Ca2+ influx through voltage-gated Ca2+ channels, and of the subtypes of such channels present in these cells, influx through N-type was primarily responsible for triggering exocytosis. L-type channels played a minor role in mediating K+-evoked secretion, whereas P/Q-type channels did not appear to be involved in secretion at all. Caffeine also evoked catecholamine release from PC12 cells, but only in the presence of extracellular Ca2+. Application of caffeine in Ca2+-free solutions evoked large, transient rises of [Ca2+]i, but did not trigger exocytosis. When Ca2+ was restored to the extracellular solution (in the absence of caffeine), store-operated Ca2+ influx was observed, which evoked exocytosis. The amount of secretion evoked by this influx pathway was far greater than release triggered by influx through L-type Ca2+ channels, but less than that caused by Ca2+ influx through N-type channels. Our results indicate that exocytosis may be regulated even in excitable cells by Ca2+ influx through pathways other than voltage-gated Ca2+ channels.

Animals↗
PubMed1999

In vivo production of type 1 cytokines in healthy sickle cell disease patients.

Interleukins (IL)-1, 2, 12, and interferon (IFN)-gamma, along with soluble IL-2 receptor (sIL-2R) were measured from sera obtained from healthy sickle cell disease (SCD) patients and comparable healthy control subjects. The cytokines were assessed by enzyme-linked immunosorbent assay (ELISA) in 60 SCD patients and 58 controls. No significant detectable levels of IL-1 or IL-12 were found in the sera of either group of patients. Significantly elevated levels of IFN-gamma were measured in 20 (33%) of 60 SCD patients and 21 (36%) of 58 controls. A large subset of 18 (41%) of 43 healthy controls and a smaller subset of 12 (21%) of 58 SCD demonstrated detectable levels of IL-2. The sIL-2R levels of the SCD group (4465 +/- 552 pg/mL) were significantly higher (P < .0001) than that of controls (3473 +/- 411 pg/mL). The results revealed comparable circulating levels of all type 1 cytokines in both healthy SCD and normal control subjects, with the exception of in vivo sIL-2R production. Elevated serum levels of both IL-6 and tumor necrosis factor (TNF)-alpha have been reported previously in a significant percentage of SCD steady-state subjects. These two cytokines are known to increase sIL-2R expression and may help explain the difference between the patient populations. Immune activation markers such as sIL-2R are produced by cells that mediate host responses to infection or inflammatory stimuli. The implication of higher levels of sIL-2R in SCD is not clear, but chronic parvovirus B19 infection, chronic polyclonal activation of B cells or defective regulation of antibodies are possible explanations for the elevated levels in SCD.

Adolescent↗
PubMed1998

Hypoxia evokes catecholamine secretion from rat pheochromocytoma PC-12 cells.

We have monitored exocytosis of catecholamines from individual PC-12 cells by amperometry using carbon fiber microelectrodes in order to investigate possible secretory responses to acute hypoxia. In normoxia, no secretion was detected from cells perfused with a solution containing 5 mM K+. However, when [K+] was raised (10-100 mM), exocytotic events were observed. Hypoxia (PO2 11 mmHg) stimulated secretion from PC-12 cells, and in hypoxic conditions exocytosis was greater at each [K+] studied as compared with normoxia. Hypoxia-evoked secretion was abolished in Ca2+ free solutions containing 1 mM EGTA and by the non-specific Ca2+ channel blocker, Cd2+ (200 microM). Secretion was also largely inhibited by omega-conotoxin GVIA (1 microM). Exocytosis was also observed in normoxia when cells were exposed to tetraethylammonium (1-10 mM), but not 4-aminopyridine (3 mM). Our findings indicate that hypoxia evokes exocytosis via depolarization arising from inhibition of a TEA-sensitive K+ conductance, leading to Ca2+ influx primarily via N-type Ca2+ channels.

Animals↗