oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2018 ( 1 )

2017 ( 1 )

2015 ( 21 )

2014 ( 31 )

Custom range...

Search Results: 1 - 10 of 335 matches for " Lakshminarayanan Aravind "
All listed articles are free for downloading (OA Articles)
Page 1 /335
Display every page Item
Female Anopheles gambiae antennae: increased transcript accumulation of the mosquito-specific odorant-binding-protein OBP2
Seth A Hoffman, Lakshminarayanan Aravind, Soundarapandian Velmurugan
Parasites & Vectors , 2012, DOI: 10.1186/1756-3305-5-27
Abstract: Our initial focus is on odorant binding proteins with differential transcript accumulation between female and male mosquitoes. We report that the odorant binding protein, OBP2 (AGAP003306), had increased expression in the antennae of female vs. male Anopheles gambiae sensu stricto (G3 strain). The increased expression in antennae of females of this gene by quantitative RT-PCR was 4.2 to 32.3 fold in three independent biological replicates and two technical replicate experiments using A. gambiae from two different laboratories. OBP2 is a member of the vast OBP superfamily of insect odorant binding proteins and belongs to the predominantly dipteran clade that includes the Culex oviposition kairomone-binding OBP1. Phylogenetic analysis indicates that its orthologs are present across culicid mosquitoes and are likely to play a conserved role in recognizing a molecule that might be critical for female behavior.OBP2 has increased mRNA transcript accumulation in the antennae of female as compared to male A. gambiae. This molecule and related molecules may play an important role in female mosquito feeding and breeding behavior. This finding may be a step toward providing a foundation for understanding mosquito olfactory requirements and developing control strategies based on reducing mosquito feeding and breeding success.Factors that influence mosquito fitness, especially host seeking and mate finding are complex and modulated by multiple cues, of which olfactory cues are most important [1-4]. Detection of odor molecules requires odorant binding proteins (OBPs) that are abundant in antennal chemosensilla [5,6]. OBPs are low molecular weight soluble proteins that bind and transport odor molecules from sensillae to G-protein-coupled receptors in olfactory sensory neurons [6]. The finding of receptor AgamOBP1 binding to its ligand indole demonstrated the significance of OBPs in odor recognition [7]. Understanding olfactory function could lead to development of malaria control
Using Citizens to Do Science Versus Citizens as Scientists
Shyamal Lakshminarayanan
Ecology and Society , 2007,
Abstract:
Ruminating about MOOCs
S. LAKSHMINARAYANAN
Journal of the NUS Teaching Academy , 2012,
Abstract:
A model for exploring bird morphology
Shyamal Lakshminarayanan
Quantitative Biology , 2007,
Abstract: A simplified model of the bird skeleton along with elongation parameters for the flight feathers is used to explore the diversity of bird shapes. Varying a small number of parameters simulates a wide range of observed bird silhouettes. The model may serve to examine developmental factors involved, help museum curators develop computational approaches to bird morphometry and has applications in computer generated illustration.
Action potential repolarization enabled by Ca++ channel deactivation in PSpice simulation of smooth muscle propagation
Lakshminarayanan Ramasamy, Nicholas Sperelakis
BioMedical Engineering OnLine , 2005, DOI: 10.1186/1475-925x-4-71
Abstract: In the current work, the repolarization of the AP was accomplished by inserting a second BB into the Ca++ leg of the basic membrane unit. Repolarization of the AP was produced, not through an activation of the K+ channel conductance, but rather through a mimicking of the deactivation of the Ca++ channel conductance. Propagation of complete APs was studied in a chain (strand) of 10 smooth muscle cells, in which various numbers of gap-junction (gj) channels (assumed to be 100 pS each) were inserted across the cell junctions.The shunt resistance across the junctions produced by the gj-channels (Rgj) was varied from 100,000 MΩ (0 gj-channels) to 10,000 MΩ (1 gj-channel), to 1,000 MΩ (10 channels), to 100 MΩ (100 channels), to 10 MΩ (1000 channels), and to 1.0 MΩ (10,000 channels). Velocity of propagation (θ, in cm/sec) was calculated from the measured total propagation time (TPT, the time difference between when the AP rising phase of the first cell and the last cell crossed -20 mV), assuming a constant cell length of 200 μm. When there were no gj-channels, or only one, the transmission of excitation between cells was produced by the electric field (EF), i.e., the negative junctional cleft potential, that is generated in the narrow junctional clefts (e.g., 100 A) when the prejunctional membrane fires an AP (a fraction of a millisecond before the adjacent surface membrane). There were significant end-effects at the termination of the strand, such that the last cell (cell #10) failed to fire, or fired after a prolonged delay. This end-effect was abolished when the strand termination resistance (Rbt) was increased from 1.0 KΩ to 600 MΩ. When there were 1000 or 10,000 gj-channels, the transmission of excitation was produced by local-circuit current flow from one cell to the next through the gj-channels.In summary, it is now possible to simulate complete APs in smooth muscle cells that could propagate along a single chain of 10 cells, even when there were no gj-channels betw
Transverse propagation in an expanded PSpice model for cardiac muscle with gap-junction ion channels
Lakshminarayanan Ramasamy, Nicholas Sperelakis
BioMedical Engineering OnLine , 2006, DOI: 10.1186/1475-925x-5-46
Abstract: Successful transmission of excitation from one myocardial cell to the next contiguous myocardial cell can occur without the necessity of gj-channels between the cells. This has been demonstrated to be possible in theoretical and modeling studies by Sperelakis and colleagues [1-4]. In addition, the essential phenomenon in electric field (EF) transmission has been confirmed by other laboratories, [5-7]. As was stated in the 1977 paper of Sperelakis and Mann [1], for the EF mechanism to work successfully, the junctional membrane must be more excitable than the contiguous surface sarcolemma. The fact that the junctional membranes (i.e., the intercalated disks) have a higher concentration (density) of fast Na+ channels than the surface sarcolemma [6,8-10] should cause them to be more excitable than the surface membrane.Kucera et al. [10] did a simulation study of cardiac muscle in which they determined how conduction velocity varied as a function of the gap-junction resistance (i.e., number of gj-channels) while varying the fraction of fast INa channels located in the junctional membranes. For a 10 nm (100 ?) cleft width and 50% of the INa channel located in the junctional membranes, they found that conduction still occurred at a velocity of about 20 cm/sec when cell coupling was reduced to 10% of normal. Velocity was about 10 cm/sec when coupling was 1% of normal. Consistent with our previous report [11] they observed that the EF mechanism actually slowed velocity by a significant amount when there was strong ("normal") coupling.In biological studies on connexon43 knockout mice, and therefore virtually absent in gj-channels in their hearts, it was shown that propagation velocity only was slowed, but not blocked [12-15]. And these mice survive. Therefore, it seems clear that the presence of gj-channels is not essential for propagation of excitation in the heart. But when hearts do contain gj-channels (e.g., mammals and adult birds), propagation velocity is speeded up. Th
Gap-junction channels inhibit transverse propagation in cardiac muscle
Nicholas Sperelakis, Lakshminarayanan Ramasamy
BioMedical Engineering OnLine , 2005, DOI: 10.1186/1475-925x-4-7
Abstract: We have developed an electric field hypothesis for the mechanism of transmission of excitation from one cell to the next that does not require gap-junction channels [1-4]. In the electric field hypothesis, the electrical voltage that develops in the narrow junctional cleft (Vjc) when the prejunctional membrane generates an action potential, serves to depolarize the postjunctional membrane its threshold, by a patch-clamp-like effect. The parameters that affect the magnitude of Vjc include the size of Rjc, the transverse resistance of the junctional cleft. This results in excitation of the postjunctional cell, after a brief junctional delay. The total propagation time consists primarily of the summed junctional delays. This results in a staircase-shaped propagation, the surface sarcolemma of each cell firing almost simultaneously [2].There are no low-resistance connections between the cells in several different cardiac muscle and smooth muscle preparations (reviewed in [3,4]. Propagation by mechanisms not requiring low-resistance connections have also been proposed by others [5-8]. Propagation has been demonstrated to be discontinuous (or saltatory) in cardiac muscle [9-12]. Fast Na+ channels are localized in the junctional membranes of the intercalated discs of cardiac muscle [13-15] Sperelakis, 1995, a requirement for the EF mechanism to work [3,4,1,2,13]. In connexin-43 and Cx40 knockout mice, propagation in the heart still occurs, but it is slowed [15-19], as predicted by our PSpice simulation study [20]. It was reported that the anisotropic conduction velocity observed in the heart is not a result of cell geometry [21].Subsequently, we published a series of papers on the longitudinal and transverse propagation of action potentials in cardiac muscle and smooth muscle using PSpice analysis [22,20,24]. In the review process for our recent paper [24], one of the referees asked us to determine the effect of introducing strong cell coupling via gap-junction (g-j) chann
Oral melanoacanthoma: a case report and review of the literature
Vidya Lakshminarayanan, Kannan Ranganathan
Journal of Medical Case Reports , 2009, DOI: 10.1186/1752-1947-3-11
Abstract: We present a case report of oral melanoacanthoma in a 24-year-old Asian Indian man. He presented with an intra-oral brown macular lesion on the left buccal mucosa with a duration of one and a half months. Microscopic examination revealed acanthosis of stratified squamous surface epithelium and dendritic melanocytes diffusely distributed in the epithelium; the Masson-Fontana silver impregnation technique was used to demonstrate the dendritic melanocytes. Based on the history, clinical features and histological presentation, the lesion was diagnosed as melanoacanthoma.This is the first reported instance of oral melanoacanthoma in the Indian sub-continent. This report details the course of the lesion from diagnosis to its resolution. Melanoacanthoma must be differentiated from other intra-oral pigmented lesions and biopsy may be required to rule out melanoma.Melanoacanthoma of the oral mucosa is a rare condition indicative of a reactive process [1]. Oral melanoacanthoma was first reported in 1978 [2] and to the best of our knowledge, only 50 cases of melanoacanthoma have been reported in the literature to date (Table 1) [2-14]. The clinical presentation is a brown to brown-black macular lesion, predominantly solitary, encountered in the younger age group with a distinct female predilection [3,12]. The most common site affected is the buccal mucosa. Melanoacanthoma has been reported in labial mucosa, palate, gingiva, alveolar mucosa and oropharynx (Table 1). The typical histological picture of melanoacanthoma is the proliferation of dendritic melanocytes throughout the epithelium. The epithelium exhibits acanthosis and spongiosis. A chronic inflammatory cell infiltrate with eosinophils may be noted. The lesion is benign and may regress following an incisional biopsy [1].A 24-year-old graduate dental student presented with a complaint of intra-oral pigmentation of the left buccal mucosa with duration of one and a half months. The patient had initially noted a small round
Propagation velocity profile in a cross-section of a cardiac muscle bundle from PSpice simulation
Nicholas Sperelakis, Lakshminarayanan Ramasamy
Theoretical Biology and Medical Modelling , 2006, DOI: 10.1186/1742-4682-3-29
Abstract: The velocity profile of simulated action potentials propagated down a bundle of parallel cardiac muscle fibers was examined in a cross-section of the bundle using a PSpice model. The model (20 × 10) consisted of 20 chains in parallel, each chain being 10 cells in length. All 20 chains were stimulated simultaneously at the left end of the bundle using rectangular current pulses (0.25 nA, 0.25 ms duration) applied intracellularly. The simulated bundle was symmetrical at the top and bottom (including two grounds), and voltage markers were placed intracellularly only in cells 1, 5 and 10 of each chain to limit the total number of traces to 60. All electrical parameters were standard values; the variables were (1) the number of longitudinal gap-junction (G-j) channels (0, 1, 10, 100), (2) the longitudinal resistance between the parallel chains (Rol2) (reflecting the closeness of the packing of the chains), and (3) the bundle termination resistance at the two ends of the bundle (RBT). The standard values for Rol2 and RBT were 200 KΩ.The velocity profile was bell-shaped when there was 0 or only 1 gj-channel. With standard Rol2 and RBT values, the velocity at the surface of the bundle (θ1 and θ20) was more than double (2.15 ×) that at the core of the bundle (θ10, θ11). This surface:core ratio of velocities was dependent on the values of Rol2 and RBT. When Rol2 was lowered 10-fold, θ1 increased slightly and θ2decreased slightly. When there were 100 gj-channels, the velocity profile was flat, i.e. the velocity at the core was about the same as that at the surface. Both velocities were more than 10-fold higher than in the absence of gj-channels. Varying Rol2 and RBT had almost no effect. When there were 10 gj-channels, the cross-sectional velocity profile was bullet-shaped, but with a low surface/core ratio, with standard Rol2 and RBT values.When there were no or few gj-channels (0 or 1), the profile was bell-shaped with the core velocity less than half that at the surface. In
Repolarization of the action potential enabled by Na+ channel deactivation in PSpice simulation of cardiac muscle propagation
Lakshminarayanan Ramasamy, Nicholas Sperelakis
Theoretical Biology and Medical Modelling , 2005, DOI: 10.1186/1742-4682-2-48
Abstract: We have now been able to repolarize the AP by inserting a second BB into the Na+ leg of the basic units. This second BB effectively mimicked deactivation of the Na+ channel conductance. This produced repolarization of the AP, not by activation of K+ conductance, but by deactivation of the Na+ conductance. The propagation of complete APs was studied in a chain (strand) of 10 cardiac muscle cells, in which various numbers of gap-junction (gj) channels (assumed to be 100 pS each) were inserted across the cell junctions. The shunt resistance across the junctions produced by the gj-channels (Rgj) was varied from 100,000 M? (0 gj-channels) to 10,000 M? (1 gj-channel), to 1,000 M? (10 channels), to 100 M? (100 channels), and 10 M? (1000 channels). The velocity of propagation (θ, in cm/s) was calculated from the measured total propagation time (TPT, the time difference between when the AP rising phase of the first cell and the last cell crossed -20 mV, assuming a cell length of 150 μm. When there were no gj-channels, or only a few, the transmission of excitation between cells was produced by the electric field (EF), i.e. the negative junctional cleft potential, that is generated in the narrow junctional clefts (e.g. 100 A) when the prejunctional membrane fires an AP. When there were many gj-channels (e.g. 1000 or 10,000), the transmission of excitation was produced by local-circuit current flow from one cell to the next through the gj-channels.We have now been able to simulate complete APs in cardiac muscle cells that could propagate along a single chain of 10 cells, even when there were no gj-channels between the cells.There are no low-resistance connections between the cells in several different cardiac muscle and smooth muscle preparations [1-3]. In a computer simulation study of propagation in cardiac muscle, it was shown that the electric field (EF) generated in the narrow junctional clefts when the prejunctional membrane fires an action potential (AP) depolarizes the
Page 1 /335
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.