Biomedical subjects

R Srinivasan

Publications and source records attributed to R Srinivasan.

At least 127 records · Page 7Linked to original sources

PubMed1995

Response of gravid Phlebotmus papatasi females to an oviposition attractant/stimulant associated with conspecific eggs.

Oviposition response of gravid P. papatasi females to conspecific eggs was studied in laboratory colonized sandflies. It was observed that significantly higher number of eggs were laid in the vicinity of conspecific eggs. However, a certain minimum number of eggs were required to be placed on the substratum to influence the rate of oviposition. The fecundity of females (mean = 56.5 +/- 4.9 eggs) exposed to conspecific eggs was significantly higher (P < 0.05) than that of blank control group. Perhaps, the chemical substances/pheromone of egg origin stimulated the oviposition rate. In an attempt to isolate the active ingredient, solvent washing of the conspecific eggs were tested. No increase in the rate of oviposition was noticed when the test site was treated with distilled water extract, whereas, significantly larger number of eggs were laid at the site treated with di-ethyl ether extract. This indicated that the oviposition attractant associated with the eggs dissolved in the organic solvent, but not in water. The possible application of this attractant for wild sandflies in nature and for regulating the site of oviposition on the substratum in the laboratory colonized sandflies needs to be explored.

Animals↗

PubMed1994

The T-to-R transformation in hemoglobin: a reevaluation.

The relationship between the T, R, and R2 quaternary forms of hemoglobin is examined by computational experiments. Contrary to previous suggestions, we propose that the R quaternary form may lie on the pathway from T to R2. This proposal is consistent with four independent observations. (i) Difference distance maps are used to identify those parts of the molecule that undergo conformational change upon oxygenation. The simplest interpretation of these maps brackets R between T and R2. (ii) Linear interpolation from T to R2 passes through R. (iii) The well-known "switch" region (so called because, upon transition between the T and R quaternary forms, a residue from the beta 2 subunit toggles between two stable positions within the alpha 1 subunit) progresses from T through R to R2, successively. (iv) A hitherto-undocumented feature, diagnostic of the R structure, is noted within the alpha subunit: upon transformation from T to R, the beta-turns at the amino terminal of the E and F helices flip from one turn type to another. Upon transformation from R to R2, the latter turn--a strained conformation--flips back again.

Allosteric Regulation↗

PubMed1994

Rules for alpha-helix termination by glycine.

A predictive rule for protein folding is presented that involves two recurrent glycine-based motifs that cap the carboxyl termini of alpha helices. In proteins, helices that terminated in glycine residues were found predominantly in one of these two motifs. These glycine structures had a characteristic pattern of polar and apolar residues. Visual inspection of known helical sequences was sufficient to distinguish the two motifs from each other and from internal glycines that fail to terminate helices. These glycine motifs--in which the local sequence selects between available structures--represent an example of a stereochemical rule for protein folding.

Amino Acid Sequence↗

PubMed1994

Leukemia inhibitory factor in long-term adherent layer cultures: increased levels of bioactive protein in leukemia and modulation by IL-4, IL-1 beta, and TNF-alpha.

In the current study, we used a monoclonal antibody-based enzyme-linked immunosorbent assay and bioassay to assess leukemia inhibitory factor (LIF) protein levels, activity, and function in supernatants of 59 adherent layers derived from acute and chronic myelogenous leukemia, myelodysplastic syndrome, and hairy cell leukemia patients and from normal controls. We demonstrate that biologically active LIF protein is constitutively produced and secreted by cultured bone marrow stromal cells from all of the studied subjects. Furthermore, various cytokines can alter endogenous LIF protein levels. Twenty-four h of exposure to recombinant human (rh) interleukin (IL) 4 (100 units/ml) significantly decreased LIF protein levels in adherent layer conditioned media [median base line level, 2.6 ng/ml; range, 1.6-8.0 ng/ml; median post rhIL-4 exposure levels, 1.9 ng/ml; range, 0.9-5.8 ng/ml (n = 7; P = 0.022)]. In contrast, rhIL-1 beta and rh tumor necrosis factor alpha consistently increased LIF protein levels. In the samples exposed to 50 units/ml rhIL-1 beta, median base line LIF level was 2.6 ng/ml; median post-LIF level was 9.0 ng/ml (n = 8; P = 0.014). In the two samples exposed to rh tumor necrosis factor alpha (200 units/ml), LIF levels increased from baseline levels of 2.6 and 2.7 ng/ml to postexposure levels of 7.7 and 12.2 ng/ml, respectively. Finally, the presence of LIF may be relevant to both normal and malignant hematopoietic processes as evidenced by: (a) LIF protein levels in adherent layer conditioned media were significantly elevated in samples from patients with a spectrum of hematological neoplasms [acute myelogenous leukemia: median level, 3.0 ng/ml (range, 1.6-11.0 ng/ml); myelodysplastic syndrome: median level, 4.5 ng/ml (range 1.4-15.5 ng/ml); hairy cell leukemia; median level, 3.5 ng/ml (range 2.2-10.3 ng/ml); chronic myelogenous leukemia-chronic phase: median level, 4.35 ng/ml (range 0.3-19.0 ng/ml); and chronic myelogenous leukemia-blast crisis: median level, 6.25 ng/ml (range 0.7-20.3 ng/ml)] as compared to samples from normal individuals (median level, 2.0 ng/ml; range, 0.7-4.6 ng/ml; P < 0.05); and (b) in normal controls, in vitro abrogation of endogenous LIF bioactivity by neutralizing antibody decreased the number of committed granulocyte-macrophage hemopoietic progenitors.

Blast Crisis↗

PubMed1994

Potassium permanganate resistant amyloid in fine-needle aspirate of the liver.

A case of primary amyloidosis, initially detected by fine-needle aspiration of the liver, is reported here. Amorphous acellular metachromatic material was seen extracellularly in between the hepatocytic cords compressing them. This material showed typical apple-green birefringence under crossed bipolars after alkaline Congo-red staining proved its amyloid nature. It was resistant to potassium permanganate pretreatment, indicating it to be of the AL type.

Amyloid↗

PubMed1994

Sequence determinants of the capping box, a stabilizing motif at the N-termini of alpha-helices.

The capping box, a recurrent hydrogen bonded motif at the N-termini of alpha-helices, caps 2 of the initial 4 backbone amide hydrogen donors of the helix (Harper ET, Rose GD, 1993, Biochemistry 32:7605-7609). In detail, the side chain of the first helical residue forms a hydrogen bond with the backbone of the fourth helical residue and, reciprocally, the side chain of the fourth residue forms a hydrogen bond with the backbone of the first residue. We now enlarge the earlier definition of this motif to include an accompanying hydrophobic interaction between residues that bracket the capping box sequence on either side. The expanded box motif--in which 2 hydrogen bonds and a hydrophobic interaction are localized within 6 consecutive residues--resembles a glycine-based capping motif found at helix C-termini (Aurora R, Srinivasan R, Rose GD, 1994, Science 264:1126-1130).

Amino Acid Sequence↗

PubMed1994

Two configurations of the four-ring birdcage coil for 1H imaging and 1H-decoupled 31P spectroscopy of the human head.

The four-ring birdcage resonator, a new class of dual-tuned birdcage resonators, is described. We report two configurations of the coil: the low-pass, high-pass (LP-HP) and the low-pass, low-pass (LP-LP), both of which can be operated in dual quadrature mode at 1.5 T. As head coils, both configurations exhibit greatly reduced tuning interactions between frequencies, permitting rapid, noniterative tuning. Compared with single-tuned, two-ring birdcage resonators of similar volume, the sensitivity and transmitter efficiencies of the resonators are better than 85% for the proton frequency and the same to within 5% for the phosphorus frequency. Circuit models have been developed to refine coil tuning and aid the calculation of B1 field contour plots. Both configurations have been used for integrated examinations involving acquisition of high-quality 1H images and 1H-decoupled 31P CSI spectra of the human head. A scaled-down version of the LP-LP configuration has been demonstrated for use with the human calf.

Head↗

PubMed1994

Simultaneous and interleaved multinuclear chemical-shift imaging, a method for concurrent, localized spectroscopy.

A method is proposed for carrying out chemical-shift imaging simultaneously on several nuclei (1H and 31P in this example), using a commercial clinical NMR imager fitted with a second RF channel and a dual-tuned birdcage coil to fit the human head. Nuclei of different gamma are examined at the same field of view by exciting each nucleus successively at times proportional to gamma during the same phase-encoding gradient waveform. Thus, each higher-gamma nucleus is exposed to a smaller area of the gradient. Additionally, since in vivo protons typically have a shorter T1 and roughly an order of magnitude higher sensitivity than phosphorus, it is possible to interleave 1H-only acquisitions between the simultaneous 1H, 31P observations while the lower-gamma nucleus relaxes. Consequently, additional information is obtained with either higher spatial resolution or greater sensitivity (more signal averaging) without lengthening the duration of the examination.

Computer Simulation↗

PubMed1994

A theoretical and experimental study of high resolution EEG based on surface Laplacians and cortical imaging.

Two different methods to improve the spatial resolution of EEG are discussed: the surface Laplacian (e.g., current source density) and cortical imaging (e.g., spatial deconvolution). The former methods tend to be independent of head volume conductor model, whereas the latter methods are more model-dependent. Computer simulation of scalp potentials due to either a few isolated sources or 4200 distributed cortical sources and studies of actual EEG data both indicate that the two methods provide similar estimates of cortical potential distribution. Typical correlation coefficients between either spline-Laplacian or cortical image and simulated (calculated) cortical potential are in the 0.8-0.95 range, depending partly on CSF thickness. By contrast, correlation coefficients between simulated scalp and cortical potential are in the 0.4-0.5 range, suggesting that high resolution methods provide much better estimates of cortical potential than is obtained with conventional EEG. The two methods are also applied to steady-state visually evoked potentials and spontaneous EEG. Correlation coefficients obtained from real EEG data are in the same general ranges as correlations obtained from simulations. The new high resolution methods can provide a dramatic increase in the information content of EEG and appear to have widespread application in both clinical and cognitive studies.

Brain↗

PubMed1994

Subintimal angioplasty of femoropopliteal artery occlusions: the long-term results.

The technique of subintimal angioplasty has been attempted on 200 consecutive femoropopliteal artery occlusions of median (range) length 11 (2-37) cm. The principle of the technique is to traverse the occlusion in the subintimal plane and recanalise by inflating the angioplasty balloon within the subintimal space. The technical success rate was 159/200 (80%) and was not significantly different for occlusions < 10 cm (81%, n = 73), 11-20 cm (83%, n = 63) or > 20 cm (68%, n = 23), p = 0.20. There were no deaths nor limb loss resulting from the procedure. The median (range) ankle-brachial pressure index increased from 0.61 (0.21-1.0) preangioplasty to 0.90 (0.26-1.50) postangioplasty. The actuarial haemodynamic patencies of technically successful procedures at 12 and 36 months were 71% and 58% respectively, the symptomatic patencies were 73% and 61%. A multiple regression analysis showed that smoking multiplied the risk of reocclusion by 2.70 (p < 0.001), each additional run-off vessel reduced the risk by 0.54 (p < 0.001) and the risk increased by 1.73 (p = 0.020) for every 10 cm of occlusion length. In conclusion, the technical success rate (80%) of subintimal angioplasty for femoropopliteal occlusions is unrelated to occlusion length and for all procedures, including technical failures, cumulative symptomatic and haemodynamic patencies of 46 and 48% can be achieved at 3 years. The factors influencing long-term patency were smoking, the number of calf run-off vessels and occlusion length.

Aged↗

PubMed1994

Phlebotomine sandflies (Diptera: Psychodidae) of Tamil Nadu and Pondicherry, southern India, in relation to visceral leishmaniasis.

The Phlebotomine sandfly fauna of Tamil Nadu and Pondicherry in South India is described. Two morphologically different forms of Phlebotomus argentipes, the vector of Indian visceral leishmaniasis, are reported from Madras, a known focus of visceral leishmaniasis. A new species, Sergentomyia shettyi sp. nov., is described and Sergentomyia babu and Sergentomyia insularis stat. nov. are considered distinct species on the basis of their parapatric distribution. Phlebotomus papatasi and P. argentipes were the most abundant species around houses (37% and 29% of the catch, respectively), based on 1 year's sampling in villages near Pondicherry. The incidence of visceral leishmaniasis in Tamil Nadu since 1903 is summarized.

Animals↗

PubMed1994

Relative potency of DEPA as a repellent against the sandfly Phlebotomus papatasi.

The insect repellent N,N-diethylphenylacetamide (DEPA) was compared with two commercial repellents, N,N-diethyl-m-toluamide (DEET) and dimethyl phthalate (DMP), for protection against 3-day-old unfed females of the sandfly Phlebotomus papatasi (Scopoli) under laboratory conditions, using host rabbits. Both DEPA and DEET were found to be more effective than DMP, but there was no significant difference between the efficacy of DEPA and DEET.

Acetamides↗

PubMed1994

Direct measurement of chlorine penetration into biofilms during disinfection.

Transient chlorine concentration profiles were measured in biofilms during disinfection by use of a microelectrode developed for this investigation. The electrode had a tip diameter of ca. 10 microm and was sensitive to chlorine in the micromolar range. The biofilms contained Pseudomonas aeruginosa and Klebsiella pneumoniae. Chlorine concentrations measured in biofilms were typically only 20% or less of the concentration in the bulk liquid. Complete equilibration with the bulk liquid did not occur during the incubation time of 1 to 2 h. The penetration depth of chlorine into the biofilm and rate of penetration varied depending on the measurement location, reflecting heterogeneity in the distribution of biomass and in local hydrodynamics. The shape of the chlorine profiles, the long equilibration times, and the dependence on the bulk chlorine concentration showed that the penetration was a function of simultaneous reaction and diffusion of chlorine in the biofilm matrix. Frozen cross sections of biofilms, stained with a redox dye and a DNA stain, showed that the area of chlorine penetration overlapped with nonrespiring zones near the biofilm-bulk fluid interface. These data indicate that the limited penetration of chlorine into the biofilm matrix is likely to be an important factor influencing the reduced efficacy of this biocide against biofilms as compared with its action against planktonic cells.

Biofilms↗

PubMed1994

Comparison of respiratory activity and culturability during monochloramine disinfection of binary population biofilms.

Biofilm bacteria challenged with monochloramine retained significant respiratory activity, even though they could not be cultured on agar plates. Microbial colony counts on agar media declined by approximately 99.9% after 1 h of disinfection, whereas the number of bacteria stained by a fluorescent redox dye experienced a 93% reduction. Integrated measures of biofilm respiratory activity, including net oxygen and glucose utilization rates, showed only a 10 to 15% reduction. In this biofilm system, measures of microbial respiratory activity and culturability yielded widely differing estimates of biocide efficacy.

Chloramines↗

PubMed1994

Oculocutaneous manifestations in xeroderma pigmentosa.

Xeroderma pigmentosum (XP) is a rare genetic disease characterised by defective DNA repair leading to clinical and cellular hypersensitivity to ultraviolet radiation. The oculocutaneous features of 10 patients with XP were studied retrospectively. General features included parental consanguinity (40%), familiarity (60%), onset of symptoms in first 2 years (50%), malignant skin neoplasms (60%), and carcinoma of the tongue (20%). Among the ocular features, 50% of patients presented with photophobia. Lid freckles or atrophic skin lesions were seen in all patients. Lower lid tumours were seen in 30%, chronic conjunctival congestion in 40%, corneal opacification in 40%, squamous cell carcinoma of limbus in 20%, bilateral pterygium in 40%, and visual impairment in 50%. The clinical features (ocular and cutaneous) of the cases are discussed.

Adolescent↗

PubMed1993

Sequence-specific interaction of a conformational domain of p53 with DNA.

Mutations within a conserved "conformational" domain of the p53 protein have frequently been observed in a wide variety of human cancers. A hybrid protein containing the wild-type conformational domain of p53 fused to protein A bound to calf thymus DNA and a specific p53 DNA-binding motif. Hybrid proteins containing mutations in p53 bound to DNA less efficiently than wild-type hybrid protein. In addition, competition experiments showed that mutated p53 DNA-binding motif failed to interact with p53 hybrid proteins. The DNA-binding activity of wild-type p53 hybrid protein was inhibited by the metal chelator 1,10-phenanthroline. These results demonstrate that DNA-binding activity resides in the conformational domain of p53, providing a structural model for disruption of DNA binding by mutation. Furthermore, metal ions may regulate binding of p53 to DNA by modulating its conformation.

Animals↗

PubMed1993

Effects of lower-body negative pressure on blood flow with applications to the human cardiovascular system.

The paper reports a theoretical investigation into the effects of lower-body negative pressure on blood flow through the human cardiovascular system. The human cardiovascular system is modelled as a closed network of arteries, arterioles, capillaries, venules and veins of different lengths and cross-sections. The pumping action is provided by the contraction of the ventricles. The model has been analysed using the finite-element method. The pertinent equations incorporating the effects of lower-body negative pressure for the pressures and flow velocities have been derived, and the quantitative results have been computed. Percentage changes in flow velocities, pressure drops and conductances under the application of lower-body negative pressure in the various segments and organs of the entire cardiovascular system are obtained. The lower-body negative pressure has no effect on the flow rates in carotid, ulnar and coronary arteries, nor on the supply of blood to the upper extremities, kidneys, spleen and liver. The major effects are found in the lower extremities.

Blood Vessels↗

PubMed1993

Population dynamics of Phlebotomus papatasi (Diptera:Phlebotomidae) in Pondicherry, India.

Investigations on the population dynamics of Phlebotomus papatasi were carried out. The average indoor resting density fluctuated between 16.70 and 2.25/man-hour in different seasons with a maximum density during monsoon season. There was a significant positive correlation between density and rainfall. Probability of daily survival of adult population was high in monsoon and low in summer. Both relative humidity and temperature influenced the survival. The finite rate of natural increase of the field population was maximum in October and minimum in April. The monsoon season, with moderate temperature and relative humidity was found to be favourable for the growth of P. papatasi population.

Animals↗