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M J Fenton

Publications and source records attributed to M J Fenton.

63 records · Page 4Linked to original sources
PubMed1990

Rapid activation by photolysis of nitr-5 in skinned fibres of the striated adductor muscle from the scallop.

Photolysis of nitr-5, a caged calcium molecule, has been used for rapid activation of skinned fibre bundles of a myosin-regulated muscle, the striated adductor of the scallop, Pecten maximus. Chemically skinned fibre bundles (diameter 70-200 microns) were equilibrated in solutions containing 1-3 mM nitr-5 (pCa 6.1) and then activated by ultraviolet laser pulse (25 ns). Pulse energies of 60-95 mJ gave contractions of over 90% maximum tension and a mean half-time for tension rise of 43 ms (n = 4) at 12 degrees C. Electrically stimulated bundles of intact fibres develop a tetanus with a rise half-time of 60.2 ms at 10 degrees C (n = 5) (Rall, J.A. (1981) J. Physiol. 321, 287-295, and personal communication). At lower pulse energies the skinned fibres gave smaller amplitude contractions with slower rates of rise (up to 260 ms half-time). In addition, a slower component of tension development (mean rise half-time 13.3 s) was often observed. In ATP-free solutions containing hexokinase and glucose, rigour tension developed with a delayed onset. Rapid release of ATP (0.47-0.59 mM) from photolysis of caged ATP (2 mM) at pCa 4.5 then caused a rapid contraction with a mean half-time for tension development of 17 ms (n = 4). The fast activation rates obtained by the photorelease of Ca2+ from nitr-5 are similar to those obtained with skinned skeletal fibres of actin-regulated muscle. The results imply that the rate-limiting step in excitation-contraction coupling of the scallop muscle is not the increase in sarcoplasmic Ca2+, but rather the activation of the muscle in response to this increase. The half-times of ATP-induced contractions at pCa 4.5 suggest that in a contraction activated by a rapid Ca2+ jump the process comprising ATP hydrolysis and cross-bridge cycling occurs at a somewhat faster rate than the Ca2(+)-dependent activation process which precedes it.

Adenosine Triphosphate↗
PubMed1990

Regulation of macrophage activation by IL-3. II. IL-3 and lipopolysaccharide act synergistically in the regulation of IL-1 expression.

We have previously reported that IL-3, a cytokine produced by both Th1 and Th2 type CD4+ T cells, displays macrophage-activating potential. IL-3, like IFN-gamma, readily induced functions related to Ag presentation (e.g., Ia and lymphocyte function-associated Ag-1 expression). However, in contrast to the response elicited by IFN-gamma, tumor cytotoxicity was not induced by IL-3. In this paper we have evaluated the capacity of IL-3 to regulate IL-1 expression. Our data demonstrate that although IL-3 alone was unable to induce the production of substantial IL-1 bioactivity in peritoneal exudate cells, it contributed synergistically to the induction of IL-1 bioactivity in the presence of suboptimal doses of LPS. It was of interest that IFN-gamma, which can also interact synergistically with LPS, was unable to complement the partial signals provided by IL-3 for the expression of IL-1 bioactivity, suggesting that IL-3 and IFN-gamma may be providing similar stimulatory signals in this respect. Our studies on the mechanism of synergy between IL-3 and LPS indicated that the effect of LPS did not appear to be mediated by the well-characterized LPS-inducible cytokines of macrophage origin (i.e., IL-1, alpha and beta, TNF-alpha, and IL-6). The best characterized function of IL-3 is its multicolony-stimulating activity as a CSF; in this context we also studied granulocyte-macrophage CSF and noted that it behaves similarly to IL-3 in that it can synergistically contribute to IL-1 induction. A similar, but more dramatic induction of IL-1 synthesis in response to IL-3 was demonstrated by the P388.D1 murine macrophage cell line. The kinetics and the molecular mechanism of the response of P388.D1 to IL-3 indicate several unique features of IL-3-induced IL-1 expression: 1) IL-3 itself induced IL-1 mRNA expression, which was unaccompanied by substantial production of bioactivity, either cell-associated or secreted into the culture supernatant; 2) IL-3 synergized with suboptimal doses of LPS to induce not only heightened IL-1 mRNA levels but bioactivity as well; and 3) IL-3, when combined with LPS, altered the kinetics of IL-1 message and bioactive protein production in response to LPS: IL-3 and LPS induced an early release (3 to 7 h poststimulation) of the IL-1 protein as well as a second peak of mRNA and bioactivity (at 12 to 36 h), which was not observed in response to either IL-3 or LPS alone.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Human pro-IL-1 beta gene expression in monocytic cells is regulated by two distinct pathways.

We have previously reported that the pro-IL-1 beta gene is transiently expressed in THP-1 human monocytic leukemia cells after stimulation with bacterial LPS. Herein we show differential pro-IL-1 beta gene transcription in the same cell type using two distinct stimuli. This transcriptional difference is also reflected at the level of intracellular IL-1 beta protein production. In contrast to LPS, a phorbol ester (PMA) induces a stable, non-transient population of mRNA. Furthermore, each induction pathway is operational under conditions where the other is inhibited, suggesting functional independence. Evidence is presented for post-transcriptional regulation of the two responses in THP-1 cells at the level of mRNA stability. We also demonstrate a similar dualistic response in primary monocyte-derived human macrophages as well as the human myelocytic cell line HL-60.

Cell Line↗
PubMed1988

The Nucleic Acid Blot Analyzer II. ANALYZE, an image analysis software package for molecular biology.

The Nucleic Acid Blot Analyzer, a new instrument providing high-speed imaging of 32P labeled nucleic acids, captures, stores and presents images in digital form, thus lending itself to rapid data handling and analysis as well as replacing conventional X-ray film autoradiography for many applications. A software package called ANALYZE has been specifically designed for the instrument in order to provide automatic or semi-automatic analysis for molecular biological techniques. The software includes image display manipulation, quantitative and positional analysis, as well as file maintenance utilities. The specific application of the software/hardware to various techniques is presented.

Molecular Biology↗
PubMed1987

Transcriptional regulation of the human prointerleukin 1 beta gene.

Interleukin 1 (IL 1) is a protein produced by monocytes in response to certain antigens which produces a wide variety of cellular responses in various tissues. We have studied the regulation of the human proIL-1 beta gene in THP-1 human monocytic leukemia cells. Lipopolysaccharide (LPS) induction of this gene results in an immediate and transient increase of message that rapidly falls to a low, but constant, level within 6 hr. This decrease results from a specific repression of transcription by 2 hr after stimulation. Cycloheximide inhibition of new protein synthesis causes a superinduction of IL 1 message, but does not alter the initial kinetics of message production. This presumably delays the synthesis of a labile transcriptional repressor protein and implies that the proIL-1 beta gene is under the control of both a transcriptional activator and a newly synthesized transcriptional repressor. The transient increase in mRNA production and the sustained low-level synthesis beyond the initial transient response suggest that the IL 1 protein itself may act intracellularly in a manner analogous to that described for several proto-oncogenes and cellular competence factors.

Cell Line↗
PubMed1987

Long-range interactions of multiple DNA structural transitions within a common topological domain.

Local DNA conformations that are underwound with respect to the right-handed B form are favored in negatively supercoiled DNA. However, when multiple transitional events co-exist within a common topological domain, they must compete with one another for the available free energy of negative supercoiling. Recently we developed a general theoretical model capable of predicting the behavior at equilibrium of defined sequences in a variety of competitive situations. In the present work we have applied this theory to predict the formation of Z-DNA as a function of superhelicity in stretches of d(CG)m and d(CA)n when they are forced to compete with one another in the same plasmid. The observed behavior of these competing sequences is in close accord with theoretical predictions. These results indicate that sequences separated by large distances can effect the transitional behavior of each other in a complex manner which is independent of the relative orientation of the participating segments. The pattern of transitional events is strongly dependent on levels of DNA supercoiling, ambient conditions and on the nature and number of the sequences involved. Although in the present work we apply the model specifically to the Z-DNA conformational transition, the results of this study may have general relevance to a variety of biological processes in which the helical repeat of DNA is reversibly altered, including the initial steps in transcription, replication and recombination.

Computer Simulation↗
PubMedDate not supplied

Mediator caused induction of a human bradykinin B1 receptor minigene: participation of c-Jun in the process.

The bradykinin B1 receptor (BKB1R) gene is expressed in selected tissues such as lung and kidney. In these tissues it is expressed at a very low level until induced by inflammatory mediators. Our aim has been to understand the mechanism of this regulatory process. A human BKB1R minigene was constructed. It contained a 1.8 kb promoter, the entire exon I, 1.5 kb of intron I, the entire exon II and intron II, and the luciferase gene as a reporter. Transient transfection of the minigene into SV40-transformed IMR90 cells (IMRSV) resulted in a promoter activity which was activated by the mediators, lipopolysaccharide and (LPS) desArg(10)-kallidin. In contrast, these mediators did not induce the activity of the 1.8 kb promoter construct alone. Thus, motifs exclusive of the promoter such as 5'-UTR and/or intron regions are required for mediator-induced expression of this gene. Promoter activities of both the minigene and the 1.8 kb promoter construct were enhanced in a dose-dependent manner upon cotransfection with c-Jun. Furthermore, cotransfecting c-Jun with the minigene achieved the maximal promoter activity with no further increase in response to mediators. Conversely, the induction of the minigene promoter activity by mediators was abolished upon cotransfection with a dominant negative mutant of c-Jun. Other experiments suggest that multiple AP-1 sites are interactive with the c-Jun upregulation of this gene. Taken together, these results point to c-Jun as a key intermediary in the activation of the expression of this gene by mediators. However, participation of motifs outside of the promoter are necessary to obtain this inducible expression.

Exons↗
PubMedDate not supplied

Cardiac arrests at the Cenotaph.

This report describes the case histories of three veterans who suffered cardiac arrests at the 2005 Cenotaph Remembrance Parade. All three were successfully resuscitated and admitted to the St Thomas' Hospital Coronary Care Unit. They had internal cardioverter defibrillators (ICDs) inserted and remain well. All three plan to attend Remembrance ceremonies this year. We review the evidence between emotional stress and arrhythmias and the updated National Institute for Health and Clinical Excellence (NICE) guidelines for ICDs.

Aged↗