PubMed Health⌕ Search

Biomedical subjects

V Menon

Publications and source records attributed to V Menon.

At least 91 records · Page 5Linked to original sources
PubMed1995

Decreased polysomal HSP-70 may slow polypeptide elongation during skeletal muscle atrophy.

Slowed elongation rate is the apparent cause of the rapid decrease in rat soleus muscle protein synthesis rate during non-weight bearing. We found that elongation factor 2 was not phosphorylated and thus could not explain the slowed elongation rate. However, we observed a 44 +/- 19 and 28 +/- 14% decrease in the chaperone protein 70-kDa heat-shock cognate/heat shock protein (HSC/HSP-70) associated with the polysomes after 12 and 18 h of non-weight bearing, respectively. Size-fractionated polysomes had less HSC/HSP-70 associated with the larger polysomes in 18-h non-weight-bearing soleus muscle. ATP concentration increased in the non-weight-bearing muscle, so, because ATP enhances HSC/HSP-70 dissociation, we tested the potential role of ATP. Digitonin-permeabilized myoblasts treated with increasing concentrations of ATP showed both a decreased association of HSC/HSP-70 with the polysomes and a shift toward heavier polysomes; these responses were blocked by adenosine 5'-O-(3-thiotriphosphate). These data are consistent with the role of HSC/HSP-70 as a chaperone of nascent protein. The absence of HSC/HSP-70 may slow ribosome translocation, thus slowing elongation rate.

Adenosine Triphosphate↗
PubMed1995

Decrease in heart peptide initiation during head-down tilt may be modulated by HSP-70.

This study examines the mechanism of the rapid decrease in cardiac muscle protein synthesis during rodent hindlimb non-weight bearing. Polysomes isolated from rat hearts 8 h after suspension show less RNA in the polysome pool and a shift in polysome size toward fewer ribosomes per mRNA; 18 h after suspension, the size shift persists, but the amount of RNA in the polysome pool returns to control values. These data are consistent with a decrease in the rate of initiation of protein synthesis. At both 8 and 12 h of suspension, the cardiac polysomes show a 78 and 93% increase association with the nascent polypeptide chaperone protein 70-kDa heat-shock cognate/heat-shock protein (HSC/HSP-70), respectively, that persists after 7 days of non-weight bearing. Because the dissociation of HSC/HSP-70 from unfolded protein can be modulated by ATP, we measured the adenosine nucleotide pools and found a 53% decrease in ATP levels after 18 h of suspension. We propose a mechanism in which a shift of HSC/HSP-70 to the nascent polypeptide indirectly inhibits protein synthesis initiation.

Adenosine Triphosphate↗
PubMed1995

Head-down tilt increases rat cardiac muscle eIF-2 alpha phosphorylation.

We previously demonstrated that head-down tilt in rats decreases heart polypeptide initiation rate and proposed a mechanism whereby redistribution of the chaperone heat-shock cognate/heat-shock protein-70 (HSC/HSP-70) facilitates the phosphorylation of eukaryotic initiation factor-2 alpha (eIF-2 alpha). In this study, two-dimensional gel electrophoretic analysis of eIF-2 alpha showed no phosphorylation in control hearts. At 8 h of head-down tilt, there was a 45% increase in total eIF-2 alpha, and 79% was phosphorylated. At 18 h, eIF-2 alpha increased to 142% of control, of which 4% was phosphorylated. This is consistent with the previous study where, at 8 h, there was a 78% increase in polysomal HSC/HSP-70 and a shift in the polysome center-of-mass to lighter polysomes (indicating decreased initiation). After 18 h of suspension, polysomal HSC/HSP-70 levels were 24% relative to control, and the center-of-mass returned toward control. We conclude that the decrease in polypeptide initiation during head-down tilt is mediated by HSC/HSP-70 via phosphorylation of eIF-2 alpha.

Animals↗
PubMed1995

Effects of diabetes on isometric tension as a function of [Ca2+] and pH in rat skinned cardiac myocytes.

In diabetes a primary myocardial defect occurs that is characterized by decreases in systolic pressure and cardiac output. The present study investigates whether diabetes causes a decreased maximum tension-generating ability, decreased Ca2+ sensitivity of myofilaments, or no change in cardiac myofilament contractile properties at pH 7.0 and 6.6. Hearts from Wistar rats were excised and mechanically disrupted 6-10 wk after injection of streptozotocin. The resulting myocyte-size preparations of skinned myocardium were used to determine the steady-state tension-negative, log molar Ca2+ concentration (pCa) relation. Maximum tension was unchanged, and the pCa of half-maximum tension generation was 0.14 pCa units lower than control for skinned myocytes from diabetic rats at pH 7.0. A significantly lower than normal maximum tension was observed at pH 6.6 for cardiac myocytes from diabetic rats. Increased expression of beta-myosin heavy chain (MHC) occurred in hearts from diabetic rats. Two troponin T (TnT) isoforms in myocardium of adult rats were identified by Western blots. The ratio of the two TnT isoforms were altered in diabetes. Changes in cardiac MHC and TnT expression may contribute to the observed decrease in Ca2+ sensitivity of myofilaments at pH 7.0 and decreased maximum tension-generating ability at pH 6.6 in diabetes.

Animals↗
PubMed1995

Relative afferent pupillary defect and edge light pupil cycle time in the early differentiation of central retinal vein occlusion.

A total of 37 patients of unilateral fresh central retinal vein occlusion (CRVO) of less than one month duration were examined and re-evaluated after 8 weeks. All eyes with relative afferent pupillary defect (RAPD) < or = 0.6 log units with edge light pupil cycle time (ELPCT) of 925 +/- 94 ms, visual acuity > or = 6/60 with minimal field defects proved to be of nonischemic CRVO, while eyes with RAPD > or = 0.9 log units with ELPCT of 4005 +/- 712 ms, visual acuity 3/60 with marked field defects proved to be of ischemic CRVO with evidence of retinal ischemia on fluorescein angiography. RAPD and ELPCT were found to be extremely reliable indicators for early differentiation of ischemic from nonischemic CRVO and the values remained stable over a period of time. The electroretinography (ERG) correlated well with these parameters.

Afferent Pathways↗
PubMed1994

Local estimate of surface Laplacian derivation on a realistically shaped scalp surface and its performance on noisy data.

A new implementation of the surface Laplacian derivation (SLD) method is described which reconstructs a realistically shaped, local scalp surface geometry using measured electrode positions, generates a local spectral-interpolated potential distribution function, and estimates the surface Laplacian values through a local planar parametric space using a stable numerical method combining Taylor expansions with the least-squares technique. The implementation is modified for efficient repeated SLD operations on a time series. Examples are shown of applications to evoked potential data. The resolving power of the SLD is examined as a function of the spatial signal-to-noise (SNR) ratio. The analysis suggests that the Laplacian is effective when the spatial SNR is greater than 3. It is shown that spatial low-pass filtering with a Gaussian filter can be used to reduce the effect of noise and recover useful signal if the noise is spatially incoherent.

Electricity↗
PubMed1994

Acquired immunodeficiency syndrome and health care professionals.

As health care professionals, we face a grave risk of acquiring HIV infection in the course of our work. But how many of us really know the precautions to be applied in the hospital set up in dealing with HIV infected patients? A knowledge, attitude and practice (KAP) study was conducted in Pune hospitals to assess the current status. Among the results 65% servants had not heard of AIDS, 85% nursing staff did not apply the Universal Safety Precautions (USP) approach, 13.5% resident thought that the HIV was not transmitted by blood, 30% consultants would avoid contact with an HIV positive patient. This study has shown that definite lacunae exist in knowledge specific to the particular population in question. A proposal for an education programme which is target specific and one of constant renewal is sought.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Saccadic underaction in concomitant strabismus and Hering's law: a new neurophysiologic model for binocular motor correspondence.

Hering's law of equal innervation has remained so far as an universal truth with no scientific basis. However, recent reports of Saccadic underactions in concomitant strabismus indicating asymmetric ocular motor innervation is in contradiction to the law. In an effort to understand the inequalities of binocular movements, we propose a neurophysiologic model for both normal and abnormal eye movements. The model hypothesizes that any binocular movement results from the yoking of two monocular reflex loops corresponding to the two eyes, during the plastic stage of development of ocular motor reflexes. The retinal target discrepancy triggers the reflex loop resulting in a monocular corrective movement. As there is a common binocular field, the stimuli to the two eyes are similar causing a similar binocular corrective movement. In abnormal cases coupling of asymmetric motor loops may occur resulting in alternate or unilateral saccadic underactions.

Electrooculography↗
PubMed1992

An aetiological profile of optic atrophy.

484 cases of optic atrophy were studied for the distribution pattern and significance of various etiological factors in different age groups of both sexes. Bilateral optic atrophy was found to be two and a half times as common as unilateral optic atrophy. Intracranial neoplasm (29.5%) was the most frequent known cause of bilateral optic atrophy in either sex and the most common tumor was chromophobe adenoma (48% of intracranial tumors) with highest incidence over 20 years of age. Craniopharyngioma was the most frequent tumor responsible for bilateral optic atrophy before 20 years of age. Intracranial glioma also emerged as an important cause of bilateral optic atrophy. Head injury due to road accidents and periocular trauma were the most common causes of unilateral optic atrophy in males, whereas no definite factor could be elucidated in unilateral optic atrophy in females. Vascular factors were the usual cause of optic atrophy after 40 years of age, highlighting the significance of thorough systemic evaluation.

Adolescent↗
PubMed1991

Skin test reactivity to whole body and fecal extracts of American (Periplaneta americana) and German (Blatella germanica) cockroaches in atopic asthmatics.

Forty-six atopic asthmatic subjects aged 3 to 58 years attending the allergy clinic of a university hospital were evaluated for prick skin test reactivity with commercially available extracts of cockroach (CCE) and house dust (HD). Additionally, skin testing was performed with American cockroach whole body (AWBE) and fecal extracts (AFE) as well as German cockroach whole body (GWBE) and fecal extracts (GFE) prepared in our laboratory. Commercial cockroach extract was prepared from American, German, and Oriental cockroach whole bodies. Skin test reactivity to the different extracts were as follows: 83% to HD, 70% to CCE, 70% to AWBE and/or GWBE, 63% to AWBE, 57% to GWBE, 63% to AFE and/or GFE, 52% to AFE, 50% to GFE, 48% to both AWBE and GWBE, and 39% to both AFE and GFE. The subjects with positive skin tests to AWBE and/or GWBE (70%) were the same individuals who showed skin test reactivity to CCE (70%). Subjects from lower income families (less than $10,000) had a significantly higher skin test reactivity to cockroach allergens than those from families with an annual income of $11,000 to $24,000 (P = .04). These results demonstrate the significance of cockroach sensitization in atopic asthmatics, suggest the importance of fecal cockroach allergens, and support earlier observations of shared interspecies allergens between American and German cockroach whole bodies.

Adolescent↗