Pharmacology of Adenosine Receptors of the Rat Isolated Superior Cervical Ganglion

This study has examined the effect of purines and pyrimidines on the rat superior cervical ganglion in vitro. Using an extracellular recording technique it was found adenosine and its analogues produced concentration dependent hyperpolarisations. In contrast pyrimidines such as UTP and the P2-purinoceptor agonist alpha,beta-methylene adenosine triphosphate depolarised, via a methylxanthine independent mechanism. A mechanism for the uptake and degradation of adenosine in the ganglion was evident as the effects of adenosine were enhanced in the presence of adenosine uptake inhibitors or in the presence of an adenosine deaminase inhibitor. The deaminated metabolite of adenosine, i. e. inosine was inactive. The ionic mechanism for the adenosine-induced hyperpolarisation was examined by altering the extracellular cation concentrations and the use of selective ion channel antagonists. The hyperpolarisation to adenosine was not antagonised by inorganic or dihydropyridine calcium channel antagonists, suggesting adenosine did not alter Ca2+ entry. The response to adenosine was resistant to antagonism of sodium and chloride channels and the inhibition of Na+/K+ ATPase and Na+/K+/Cl- cotransporters, but was sensitive to changes in extracellular K+ concentration. The hyperpolarisation to adenosine was enhanced in reduced external potassium solution or the presence of low concentrations of TEA suggesting adenosine may increase potassium conductance. The response to muscarinic agonists and not other agonists was selectively reduced by adenosine but not by all purines or pyrimidines. The depression of muscarine was selective for the depolarisation and not the hyperpolarisation. Both the relative order of potency of adenosine and its analogues to hyperpolarise and depress the response to muscarine were indicative of the presence of purinoceptors of the A1 subtype on the rat SCG. Studies to confirm the nature of the adenosine receptor using two selective A1-adenosine receptor antagonists. 1,3-dipropyl-8-cyclopentylxanthine and xanthine amine congener produced an apparently non-competitive inhibition. This may indicate the presence of two receptor subtypes. However, a selective A2 adenosine receptor antagonist 3,7-dimethy-1-propargyl-xanthine did not alter the inhibition of muscarinic responses or the hyperpolarisation caused by purines. The biochemical mechanism responsible for the hyperpolarisation to adenosine remains elusive. Cyclic adenosine monophosphate phosphodiesterase inhibitors Ro 20-1724 and denbufylline and an adenylate cyclase inhibitor, SQ 22,536, reduced the hyperpolarisation to purines but not the depression of the response to muscarine. However, agents known to increase cAMP levels in the ganglion did not dramatically alter the response to adenosine suggesting the responses to adenosine are not mediated by a change in cyclic nucleotide levels. The ability of phorbol esters to enhance the response to adenosine suggests that protein kinase C is involved in the interaction of adenosine with muscarine. An interaction with the arachidonic acid cascade pathway was suggested by the inhibition of the hyperpolarisation to adenosine by a selective lipoxygenase inhibitor

Demosthenes 59, Against Neaira: Introduction and Commentary

Abstract Not Provided

Heat transfer to Boiling Liquids

For the determination of the boiling film coefficients a knowledge of the temperature drop across the film under investigation is necessary. The bulk temperature of the liquid inside the evaporator is measured by a travelling thermocouple and the temperature of the tube wall, very near the film, at various levels are measured by fixed thermocouples. The installation of these thermocouples in the tube wall is a skilful and at the same time troublesome job. This laborious method has been avoided by finding out the combined annular film and wall coefficients, the value of which has been used in finding out the individual film coefficient from the general equation of the interrelationship between the overall heat transfer coefficient and the individual coefficients. An almost constant high value of the annular film coefficient has b6en assured by passing hot water through the outer annulus at a constant temperature and a constant high velocity. Boiling film coefficients of water in natural circulation vertical evaporator, with stainless steel tube and copper tube under low pressure and in Kestner evaporator at atmospheric pressure have been determined. Boiling film coefficients of organic liquids, ethyl alcohol and toluene, have been determined at low pressure in copper tube natural circulation vertical evaporator. In a forced circulation copper tube vertical evaporator the film coefficients of water, alcohol and toluene have been determined at boiling points below the atmospheric. All the observed film coefficients in different evaporators have been correlated with dimensional equations. In a pyrex glass tube natural circulation vertical evaporator the nature and the mechanism of boiling have been studied with water, alcohol, toluene and a solution of a frothing agent in water when the feed liquids are both saturated with and free from dissolved air. Attempts have been made to determine the latent heat of vapourisation of toluene at different temperatures

The Spectroscopy of Nuclear Gamma-Rays

Abstract Not Provided

Problems Associated With the Expenditure of the Energy of Particles and Radiations

Abstract Not Provided

Haemorrhagic Shock in Pregnancy

Abstract Not Provided

Combustion in a Gas Stream: Studies in Flame Spreading and Flame Stability

Abstract Not Provided

A Controlled Study of Leucotomy

Abstract Not Provided

Solvolytic Studies in the Bicyclononane Field

Cis- and trans-3-allylcyclohexanol have been synthesised and the kinetics and products of buffered acetolysis of the corresponding tosylates investigated. No double bond participation was observed either in the solvolysis products or in the kinetic behaviour. Exo- and endo-2-bicyclo(3,3,1)nonanol,exo- and endo-6-bicyclo(3,2,2)nonanol and exo- and endo-2-bicyclo(4,2,1)nonanol have been synthesised (the latter two in insufficient epimeric purity for study) and the kinetics and products of buffered acetolysis of the corresponding tosylates have been studied. Interesting kinetic behaviour has been uncovered here and explanations for this are outlined in the text. An exciting non-classical/classical ion interplay has been observed and with the evidence obtained to date, it appears that in this series of isomeric bicyclononyl p-toluenesulphonates, which represents three Wagner/Meerwein related pairs of tosylates, the extent of neighbouring carbon-carbon bond participation and non-classical behaviour varies greatly throughout this series. Thermodynamic parameters are extensively employed as supporting evidence for the proposed intermediacy of a flexible 'twin-twist boat' conformation in the solvolysis of endo-2-bicyclo(3,3,1)nonyl tosylate, and proposals are outlined for future experiments designed to provide more information on the nature of this intermediate

DNA Damage Recognition Proteins and Their Involvement in Cisplatin Resistance

cis-Diamminedichloroplatinum(II) (CDDP) is a chemotherapeutic agent widely used in the treatment of various types of cancer. Its mechanism of cytotoxicity is unclear although it is believed that DNA is the critical target. CDDP binds to DNA forming a variety of adducts including intrastrand adducts, interstrand adducts, monofunctional adducts and DNA-protein crosslinks. This thesis presents evidence that there are protein(s) present in mammalian cells which recognise CDDP-damaged DNA, To assay for these DNA damage recognition proteins (DDRPs) conditions for two very separate assays were developed. The gel mobility shift assay, which detects protein complexes under non-denaturing conditions, identified two retardation complexes which bound to CDDP damaged DNA in human, murine and feline tumour cell extracts. Binding of these complexes is shown to CDDP treated oligonucleotide of 54 base pairs but not to a CDDP treated oligonucleotide of 27 base pairs, therefore suggesting binding is dependent on having normal DNA duplex. The other system used in the detection of the DDRPs is the South-Western assay. This allowed the detection of proteins of sizes 25, 50, 100KD binding to CDDP treated DNA. The proteins in the South-Western system are run under denaturing conditions. It is not entirely clear as to whether the proteins detected in both systems are the same or whether they represent entirely different species. CDDP has been reported to bind to DNA and cause areas of singlestrandedness around the adducts. The results presented in this thesis demonstrate that the 50KD and 100KD DDRP which bind to CDDP treated double-stranded DNA may also have an affinity for single-stranded DNA. The 25KD DDRP, however, only recognises double-stranded DNA treated with CDDP suggesting that it is recognising the CDDP adducts and not the areas of single-strandedness generated around the adducts. Resistance to CDDP proves a major problem area in treatment regimes. Many cell lines resistant to CDDP have been derived in vitro by multiple exposures to the drug. Many mechanisms of resistance to CDDP have been suggested from these lines. If a role of the DDRPs was to process damage in the DNA then cell lines resistant to CDDP may show an increase in expression of the DDRPs. This thesis presents evidence that an ovarian tumour cell line resistant to CDDP in comparison to its parental line shows an increase in the binding to the 50KD and 100KD DDRPs. Work in chapter 5 presents the isolation of CDDP resistant cell lines, by acute exposure to the drug, with an increase of up to seven fold resistance levels. Evidence is presented for the resistant clones being of a mutational origin. Resistant variants occur at a frequency of 3.2x10e-6 per viable cell. This frequency can be increased to 3.4x10e-5 by treatment of the cells with the chemical mutagen ethyl methane sulphonate, EMS. The CDDP resistant phenotype is maintained after six months growth in drug free medium. This single step selection may provide clones which are more clinically relevant than the lines isolated by multiple exposures to CDDP. They may therefore provide a superior model for the study of drug resistance mechanisms to CDDP. However examination of the DDRPs showed no detectable difference in the resistant clones derived from the A2780 human ovarian tumour cell line. The thesis therefore presents evidence of the existence of DDRPs in mammalian cells. The role of these damage recognition proteins will be discussed