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Biomedical subjects

R Ramasamy

Publications and source records attributed to R Ramasamy.

At least 91 records · Page 5Linked to original sources
PubMed1993

Shortcomings of some currently available DNA probes for malaria detection.

A non-radioactive DNA probe based-method for detecting malaria will greatly aid epidemiological studies. Using putative Plasmodium falciparum and P. vivax-specific 18S ribosomal RNA directed oligonucleotides, different enzymatic and chemiluminescent detection methods were attempted without success. The sensitivity of the corresponding 32P-labelled probes was found to be inadequate. A published procedure based on chemiluminescent detection of repetitive DNA sequences of P. falciparum was found to be adequately sensitive but lacking in specificity.

Base Sequence↗
PubMed1992

Ionophore-induced Cl- transport in human erythrocyte suspensions: a multinuclear magnetic resonance study.

To investigate the effect of ionophores on Cl- distribution in human erythrocyte suspensions, we measured the membrane potential by using 19F and 31P NMR methods. Incubation of human erythrocytes with 0.005 mM of the neutral ionophores valinomycin and nonactin resulted in membrane potentials of -21.2 and -17.8 mV in the presence and absence of DIDS. However, 0.020 mM of the carboxylic ionophores lasalocid, monensin, and nigericin yielded membrane potentials similar to those measured in the absence of ionophore (-9.4 mV). In methanol, the 35Cl- NMR linewidth in the presence of valinomycin was twice as broad as those observed in the presence of carboxylic ionophores, suggesting that neutral ionophores induce Cl- efflux in part via ion pairing.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1992

High seasonal malaria transmission rates in the intermediate rainfall zone of Sri Lanka.

Malaria transmission was studied at Nikawehera, a long-established farming village, located in the intermediate rainfall zone of Sri Lanka. Observations were made over a 12-month period (October-September) that included the main rainy season which occurred during the north-east monsoon in November-January. Anolpheles culicifacies, the recognized vector of malaria in Sri Lanka, was the predominant anopheline mosquito collected by human night baiting at Nikawehera. High entomological inoculation rates with An. culcifacies (0.12/hour for Plasmodium vivax) were observed during the height of the transmission season which occurs during, and immediately after, the north-east monsoon. Anolpheles subpictus was identified as a possible additional vector at Nikawehera. Anopheles annularis, a major vector at Weheragala, a site in a new irrigation development (the Mahaweli Scheme) located 70 km away in the dry zone, was not collected by human baiting at Nikawehera. Clinical, entomological and parasitological data suggest that malaria is hyperendemic at Nikawehera, with high seasonal transmission rates.

Adolescent↗
PubMed1992

Host immunity to mosquitoes: effect of antimosquito antibodies on Anopheles tessellatus and Culex quinquefasciatus (Diptera: Culicidae).

Rabbit antibodies to antigens derived from the tissues of sugar-fed Anopheles tessellatus Theobald were fed to An. tessellatus and Culex quinquefasciatus Say in blood meals. These antibodies tended to reduce the number of eggs produced by An. tessellatus, but had no effect on the fecundity of Cx. quinquefasciatus. Ingestion of the rabbit antibodies did not detectably affect the mortality of An. tessellatus but increased the mortality of Cx. quinquefasciatus. The results provide preliminary evidence for the potential of antimosquito antibodies to disrupt the physiology of mosquito vectors and indicate the need for further studies with high-titer, monospecific antibodies against the relevant target antigens.

Animals↗
PubMed1992

Determination of chloride potential in perfused rat hearts by nuclear magnetic resonance spectroscopy.

Isolated beating rat hearts were perfused with trifluoroacetamide (TFM) and trifluoroacetate (TFA) and monitored by 19F-nuclear magnetic resonance (NMR). The average membrane TFA potential in spontaneously beating rat hearts, calculated according to standard principles assuming that TFA is distributed in its anionic form, was found to be -36.2 +/- 3.2 mV (n = 9) under normoxic conditions. In separate experiments, the chloride and potassium potentials were determined to be -38.5 +/- 3.6 mV (n = 7) and -85.3 +/- 3.3 mV (n = 7), respectively, from freeze-clamped heart tissue. In the presence of the anion-exchange inhibitor, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS), TFA uptake into heart was significantly reduced, suggesting that TFA uptake occurs partly via the Cl(-)-HCO3- exchanger. Based on these results and the results of R. E. London and S. A. Gabel (Biochemistry 28: 2378-2382, 1989), we conclude that the distribution of TFA in hearts reflects the chloride potential (ECl) and not the membrane potential. A time-dependent change in the ECl occurs during global ischemia, and changes in ECl were also observed when the hearts were perfused with high concentrations of KCl. These results demonstrate that 19F-NMR may be utilized to monitor the ECl of perfused hearts under a variety of conditions.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1992

Malaria transmission at a new irrigation project in Sri Lanka: the emergence of Anopheles annularis as a major vector.

Malaria transmission was studied in a newly irrigated area of the Mahaweli project in the dry zone of Sri Lanka. Observations were performed for a three-month period following the northeast monsoon. Parasitemia in the population varied from 20.2% in February to 7% in May, and infection was due to both Plasmodium falciparum and P. vivax. Night catches of mosquitoes collected with human bait included a high proportion of Anopheles annularis. Mosquitoes containing sporozoites in the salivary glands were identified by an enzyme-linked immunosorbent assay. Anopheles culicifacies, An. annularis, and An. aconitus were all implicated as vectors in the area. The highest entomologic inoculation rate, 0.12 infected bites/hr, was observed with An. annularis and P. vivax in March. We suggest that a change in the ecosystem from dry zone forest to irrigated cultivated land is the cause of the increased prevalence of An. annularis in this area and its emergence as a major vector of malaria.

Adolescent↗
PubMed1992

Observations on malaria patients seeking treatment in hospitals in a rural and an urban area of Sri Lanka.

Malaria in Sri Lanka is endemic in the dry zone and occurs during epidemics in the wet zone. A survey was carried out on malaria patients presenting at a hospital located in a predominantly rural area in the dry zone (Polonnaruwa) and an urban area in the wet zone (Ragama). Higher incidence of Plasmodium falciparum infections than reported nationally were observed in both locations. Of particular interest is the rapidity with which patients gained access to hospital treatment after the onset of malaria symptoms. The observed mode is 3-6 days. It is postulated that early treatment may impair the development of clinical immunity to malaria in the Sri Lankan population.

Adolescent↗
PubMed1991

NOTPME: a 31P NMR probe for measurement of divalent cations in biological systems.

1,4,7-Triazacyclononane-N,N',N''-tris(methylenephosphonate monoethylester) (NOTPME) has been synthesized, characterized and analyzed for use as a 31P NMR indicator of intracellular Mg2+ and Zn2+ ions. The 31P NMR spectrum of this chelate in the presence of metal ions shows characteristic resonances for the free chelate, Mg(NOTPME)-, Zn(NOTPME)-, and Ca(NOTPME)-. The Kd values indicate that this chelate has a 10-fold higher affinity for Mg2+ than for Ca2+ at physiological pH values. In the presence of Mg2+, NOTPME is readily loaded into red blood cells. A 31P NMR spectrum of red cells taken after several washings shows resonances characteristic of entrapped NOTPME and the Mg(NOTPME)- complex, the relative areas of which report an intracellular free Mg2+ concentration of 0.32 mM. The 31P chemical shifts of the free chelate and its metal complexes are far downfield from the typical phosphorus-containing metabolites observed in biological systems, thus making it possible to monitor intracellular cation concentrations and cell energetics simultaneously.

Cations, Divalent↗
PubMed1991

Antigenic similarity between the mosquito vectors of malaria and filariasis.

Rabbit antisera were raised to the malaria vector Anopheles tessellatus, head-thorax, abdomen, and midgut preparations. Reactivity of the antisera with An. tessellatus and the filariasis vector, Culex quinquefasciatus, were examined by enzyme-linked immunosorbent assay (ELISA) and Western blots. Although many antigens were shared between the two species of mosquitoes, tissue- and species-specific antigens also were identified.

Animals↗
PubMed1991

Influence of cardiac pacing on intracellular sodium in the isolated perfused rat heart.

Increased myocardial contractile tension has been described as being associated with increased heart rate. This phenomenon is believed due to greater sodium influx than efflux, resulting in accumulation of intracellular sodium. Sodium-23 nuclear magnetic resonance spectroscopy in combination with extracellular shift reagents offers near-continuous measurements of intracellular sodium that may be correlated with mechanical performance. In this study, the influence of cardiac pacing on intracellular sodium (Na+i), was examined in the isolated perfused rat heart using the paramagnetic shift reagent, Tm(DOTP)5-. The effect of changing heart rate on mechanical performance was measured using a pressure transducer-tipped catheter or a fluid-filled catheter during spectroscopic observation. There was no significant change in Na+i with increasing heart rate over a wide range of heart rates, and a fall in developed pressure with increasing heart rate (negative force-frequency relationship) was observed. It is concluded that the concentration of intracellular sodium monitored by this method is not sensitive to changes in heart rate.

Animals↗
PubMed1991

Repeat regions of malaria parasite proteins: a review of structure and possible role in the biology of the parasite.

Tandemly repeated amino acid sequences are characteristic of many malaria parasite proteins that have been sequenced to date. Strong selective pressures must exist to maintain the repeat regions and also to diversify them in the case proteins containing strain-variant repeats. Repeats have been suggested to function in immune-evasion and in binding to host receptors. This article focuses on the structural characteristics of the repeats in relation to their postulated function.

Amino Acid Sequence↗
PubMed1990

Nuclear magnetic resonance studies of lithium transport in erythrocyte suspensions of hypertensives.

We have applied a nuclear magnetic resonance (NMR) method, based on the 7Li nucleus, to discriminate between intracellular and extracellular lithium ions (Li+) in red blood cell (RBC) suspensions. The NMR method was compared with atomic absorption, a technique that requires physical separation of intra- and extracellular Li+ prior to chemical analysis. The rates and rate constants of RBC Na(+)-Li+ countertransport measured by the 7Li NMR method correlated significantly with the measurements made by atomic absorption for both the hypertensive (r = 0.964) and control (r = 0.961) groups. The rates of RBC Na(+)-Li+ countertransport measured by NMR were significantly higher for hypertensive patients than for normotensive controls. The fact that the NMR method does not require cell membrane lysis, and its potential to reveal structural and mechanistic information on Li+ binding and transport in cellular systems, makes it promising for understanding the basis of Li+ transport variations in RBCs, and possibly other tissues, from hypertensive patients.

Adult↗
PubMed1990

Characterisation of an inhibitory monoclonal antibody-defined epitope on a malaria vaccine candidate antigen.

A monoclonal antibody that recognizes a recently characterised 45-kDa merozoite surface antigen of the human malaria parasite Plasmodium falciparum inhibits the growth of the asexual blood stages of the parasite in vitro. The corresponding epitope has been determined by testing the reactivity of the antibody with sequentially overlapping octapeptides. A synthetic peptide containing the epitope elicits antibodies that react with the native antigen. Epitope mapping in this manner is useful in the design of synthetic vaccines against malaria.

Amino Acid Sequence↗