Biomedical subjects

S W Botchway

Publications and source records attributed to S W Botchway.

7 recordsLinked to original sources

PubMed2004

Gap junction communication dynamics and bystander effects from ultrasoft X-rays.

Gap junctions provide a route for small molecules to pass directly between cells. Toxic species may spread through junctions into 'bystander' cells, which may be exploited in chemotherapy and radiotherapy. However, this may be prevented by junction closure, and therefore an understanding of the dose-dependency of inhibition of communication and bystander effects is important. Low-energy ionising radiation (ultrasoft X-rays) provides a tool for the study of bystander effects because the area of exposure may be carefully controlled, and thus target cells may be clearly defined. Loss of gap junction-mediated intercellular communication between irradiated cells was dose-dependent, indicating that closure of junctions is proportional to dose. Closure was associated with hyperphosphorylation of connexin43. Inhibition of communication occurred in bystander cells but was not proportional to dose. Inhibition of communication at higher radiation doses may restrict the spread of inhibitory factors, thus protecting bystander cells. The reduction in communication that takes place in bystander cells was dependent on cells being in physical contact, and not on the release of signalling factors into the medium.

Animals↗

PubMed2002

Measurement of long-range repulsive forces between charged particles at an oil-water interface.

Using a laser tweezers method, we have determined the long-range repulsive force as a function of separation between two charged, spherical polystyrene particles (2.7 microm diameter) present at a nonpolar oil-water interface. At large separations (6 to 12 microm between particle centers) the force is found to decay with distance to the power -4 and is insensitive to the ionic strength of the aqueous phase. The results are consistent with a model in which the repulsion arises primarily from the presence of a very small residual electric charge at the particle-oil interface. This charge corresponds to a fractional dissociation of the total ionizable (sulfate) groups present at the particle-oil surface of approximately 3 x 10(-4).

Journal Article↗

PubMed2001

The dynamics of the relay loop tryptophan residue in the Dictyostelium myosin motor domain and the origin of spectroscopic signals.

Steady-state and time-resolved fluorescence measurements were performed on a Dictyostelium discoideum myosin II motor domain construct retaining a single tryptophan residue at position 501, located on the relay loop. Other tryptophan residues were mutated to phenylalanine. The Trp-501 residue showed a large enhancement in fluorescence in the presence of ATP and a small quench in the presence of ADP as a result of perturbing both the ground and excited state processes. Fluorescence lifetime and quantum yield measurements indicated that at least three microstates of Trp-501 were present in all nucleotide states examined, and these could not be assigned to a particular gross conformation of the motor domain. Enhancement in emission intensity was associated with a reduction of the contribution from a statically quenched component and an increase in a component with a 5-ns lifetime, with little change in the contribution from a 1-ns lifetime component. Anisotropy measurements indicated that the Trp-501 side chain was relatively immobile in all nucleotide states, and the fluorescence was effectively depolarized by rotation of the whole motor domain with a correlation time on 50-70 ns. Overall these data suggest that the backbone of the relay loop remains structured throughout the myosin ATPase cycle but that the Trp-501 side chain experiences a different weighting in local environments provided by surrounding residues as the adjacent converter domain rolls around the relay loop.

Adenosine Diphosphate↗

PubMed2000

Luminescence imaging microscopy and lifetime mapping using kinetically stable lanthanide(III) complexes.

The sensitised luminescence from stable lanthanide complexes (1 and 2) bearing a phenanthridine antenna has been used to generate time-resolved images of silica particles. The millisecond order luminescent lifetime of these complexes is utilised to demonstrate time-gated imaging of the sample from a fluorescent background and to facilitate lifetime mapping over the area of the sample.

Europium↗

PubMed1998

Novel visible and ultraviolet light photogeneration of hydroxyl radicals by 2-methyl-4-nitro-quinoline-N-oxide (MNO) and 4,4'-dinitro-(2,2')bipyridinyl-N,N'-dioxide (DBD).

Chemicals that upon absorption of light generate hydroxyl radicals (.OH), free of other damaging species under physiological conditions, are useful tools for the study of the biological effects of .OH radical and for its utilization for analytical purposes. We report the novel property of 2-methyl-4-nitro-quinoline-N-oxide (MNO) and 4,4'-dinitro-(2,2')bipyridinyl-N,N'-dioxide (DBD) to act as photogenerators of .OH with UV and visible light. Upon irradiation with 360-400 nm light MNO and DBD generate free radicals that convert coumarin carboxylic acid (CCA) to fluorescent 7-OH-CCA; the .OH radical scavengers dimethylsulfoxide (DMSO) and ethanol eliminate the induction of 7-OH-CCA fluorescence. Upon 400 nm illumination in the presence of MNO, supercoiled plasmid DNA is converted to circular and strand breakage is significantly reduced in the presence of DMSO and completely absent in the absence of MNO. The conversion of CCA to 7-OH-CCA and of supercoiled plasmid to circular DNA are also observed in the absence of oxygen. Taken together, these data indicate that MNO and DBD constitute novel .OH-generating compounds. Because currently known .OH-photogenerating compounds require UV illumination (< 360 nm) that also damages DNA and cells directly, the property of MNO to generate .OH upon 400 nm illumination is advantageous when studies on cells, DNA and other biomolecules are conducted.

2,2'-Dipyridyl↗

PubMed1997

Induction and rejoining of DNA double-strand breaks in Chinese hamster V79-4 cells irradiated with characteristic aluminum K and copper L ultrasoft X rays.

Characteristic aluminum K (AlK) (energy of 1.5 keV) and copper L (CuL) (energy of approximately 0.96 keV) ultrasoft X rays have been used to investigate the effectiveness of the numerous low-energy secondary electrons produced by low-linear energy transfer (LET) ionizing radiation. Cellular inactivation and induction and rejoining of DNA double-strand breaks (DSBs) in Chinese hamster V79-4 cells irradiated as monolayers with these ultrasoft X radiations have been studied under aerobic and anaerobic conditions. The mean cell thickness, determined by confocal laser scanning fluorescence microscopy, was used to calculate the mean dose to the nucleus of the irradiated cells. Relative to 60Co gamma rays, the relative biological effectiveness (RBE) for cellular inactivation at 10% survival is 1.7 +/- 0.1 and 2.3 +/- 0.3 for AIK and CuL ultrasoft X rays, respectively. The RBE values for induction of DSBs of 2.5 +/- 0.2 and 3.0 +/- 0.3 for AlK and CuL X rays, respectively, were determined after irradiation at 277 K using the technique of pulsed-field gel electrophoresis. Induction of DSBs is linearly dependent on dose. Oxygen enhancement ratios of 1.9 and 2.1 for cellular inactivation and DSB induction, respectively, were obtained with AIK X rays. These values are less than those for 60Co gamma radiation. The repair kinetics for rejoining of DSBs after a dose of 15 Gy is similar for both X-ray energies and 60Co gamma rays with a first half-life of 18-22 +/- 5 min. From these studies, it is suggested that induction of DSBs by low-LET radiations such as 60Co gamma rays reflects clustered damage produced predominantly by low-energy electron "track ends," which represent about 30% of the total dose.

Aerobiosis↗

PubMed1995

193 nm light induces single strand breakage of DNA predominantly at guanine.

Irradiation of DNA with 193 nm light results in monophotonic photoionization, with the formation of a base radical cation and a hydrated electron (phi PI = 0.048-0.065). Although > 50% of the photoionization events initially occur at guanine in DNA, migration of the "hole" from the other bases to guanine occurs to yield predominantly its radical cation or its deprotonated form. From sequence analysis, the data reveal that 193 nm light induces single strand breaks (ssb) in double-stranded DNA preferential 3' to a guanine residue. However, it has previously been reported that 193 nm light yields very low yields of ssb (< 2% of the yield of e-aq). The distribution of these ssb at guanine is nonrandom, showing a dependence on the neighboring base moiety. The efficiency of ssb formation at nonguanine sites is estimated to be at least one order of magnitude lower. The preferred cleavage at guanine is consistent with migration and localization of the electron loss center at guanine. It is argued that singlet oxygen and the photoionized phosphate group of the sugar moiety are not major precursors to ssb. At present, the mechanisms of strand breakage are not known although a guanine radical or one of its products remain potential precursors.

Base Sequence↗