Search PubMed⌕ Search

Biomedical subjects

V N Reddy

Publications and source records attributed to V N Reddy.

At least 109 records · Page 6Linked to original sources
PubMed1980

Calcium transport in the lens.

Evidence based on the following three observations suggests the existence of a calcium transport system in the mammalian lens: calcium levels in the lens are lower than that measured in the aqueous humor; calcium efflux is temperature-dependent and is reduced by inhibitors of Ca++ transport; and there exists a calcium-acivated, magnesium-dependent ATPase. In rat, bovine, dog, and rabbit lenses, the concentration of total calcium was found to be approximately 0.2 mM, at least an order of magnitude lower than that found in the aqueous humor. To determine the nature of the mechanism responsible for maintaining these low levels, calcium fluxes were measured. During the initial rapid phase of 45Ca efflux, the rate at 4 degrees C was reduced by 85% compared with that found at 37 degrees C. Efflux was not altered in the absence of external Na+. Calcium efflux was reduced, however, by lanthanum and propranolol, inhibitors of Ca/Mg ATPase. The presence of Ca/Mg ATPase was also demonstrated in the rat, bovine, and rabbit lens and was likewise inhibited by both lanthum and propranolol.

Animals↗
PubMed1980

Studies on lens proteins. III. Variations in polypeptides of lens beta-crystallins.

Relative amounts of two water-soluble beta-crystallin polypeptides with molecular weights of 26,000 (26K) and 28,000 daltons (28K) were measured in a number of species and also in different age groups of rats. The data indicate an age-dependent increase in the quantity of the 26K which is concomitant with a decrease in the 28K polypeptide. The ratio of these two polypeptides in the total water-soluble fraction is similar to that observed in the purified beta-crystallins. Purified beta 3-crystallin of the rabbit and its equivalent "beta L" of the bovine lens display charge heterogeneity upon DEAE chromatography, suggesting subtle qualitative changes in these crystallins. The presence of these two polypeptides in the urea-soluble fraction of lens preparations is also an indication of qualitative changes. The 26K polypeptide of beta-crystallins studied here is different from the 26K main intrinsic membrane protein in that, unlike the latter, it does not aggregate upon heating in SDS-buffer.

Age Factors↗
PubMed1979

Rhesus monkey aqueous humor composition and a primate ocular perfusate.

The composition of rhesus monkey aqueous humor has been studied in large-volume, pooled samples. Replicate determinations of the concentrations of a number of constituents have been carried out for both aqueous humor and serum from large veins by means of automatic analyzing equipment. Since aqueous humor has been obtained by anterior chamber paracentesis, it is a mixture of anterior and posterior chamber aqueous. When compared to serum, the pooled aqueous contains an excess of chloride, bicarbonate, ascorbate, lactate, uric acid, and several neutral amino acids. Rhesus monkey aqueous humor is deficient in calcium, urea nitrogen, phosphates, glucose, protein, creatinine, iron, bilirubin, cholesterol, triglycerides, a number of serum enzymes, acidic and basic amino acids, and several neutral amino acids. Sodium, potassium, magnesium, and two neutral amino acids (cysteine and valine) are of equal concentration in aqueous humor and serum. Glutathione concentration is very low in both aqueous humor and serum. Pooled rhesus monkey aqueous humor and serum are isosmolar, with measured osmolality being about 303 mOsm. Based upon the chemical analysis, a new solution has been formulated to substitute for primate aqueous humor during anterior ocular perfusion. This new solution causes very little change in the physiologic integrity of the outflow pathways during prolonged, repeated perfusion. In this respect, its effects are very similar to those of pooled rhesus monkey aqueous humor during perfusion of rhesus monkey eyes. In contrast, perfusion of rhesus monkey eyes with glutathione-bicarbonate-Ringer's solution has been shown to cause progressive increase of the total facility. To minimize physiologic alterations during operative procedures, a solution similar to this new one could be formulated for irrigation of the inside of the human eye.

Animals↗
PubMed1979

The effects of X-irradiation on lens reducing systems.

Studies have been made of the effects of X-ray on various lens reducing systems, including the levels of NADPH and glutathione (GSH), the activity of the hexose monophosphate shunt (HMS) and of certain enzymes, including GSH reductase, GSH peroxidase, and glucose-6-phosphate dehydrogenase (G-6-PG). It was found that during several weeks following X-irradiation but prior to cataract formation, there was very little change in the number of reduced -SH groups per unit weight of lens protein but that, with the appearance of cataract, there was a sudden loss of protein -SH groups. In contrast, the concentration of GSH in the X-rayed lens decreased throughout the experimental period. Similarly, the concentration of NADPH in the X-rayed lens was found to decrease significantly relative to controls 1 week prior to cataract formation, and the ratio of NADPH to NADP+ in the lens shifted at this time period from a value greater than 1.0 in the control lens to less than 1.0 in the X-rayed lens. A corresponding decrease occurred in the activity of the HMS in X-rayed lenses as measured by culture in the presence of 1-14C-labeled glucose, G-6-PD was partially inactivated in the X-rayed lens. Of the eight enzymes studied, G-6-PD appeared to be the most sensitive to X-irradiation. The data indicate that X-irradiation results in a steady decrease in the effectiveness of lens reducing systems and that when these systems reach a critically low point, sudden oxidation of protein -SH groups and formation of high-molecular-weight protein aggregates may be initiated.

Animals↗
PubMed1978

Studies on lens proteins. I. Subunit structure of beta crystallins of rabbit lens cortex.

A method has been developed to isolate and characterize beta-crystallins of rabbit lens cortex. Chromatographic separation of water-soluble structure proteins of rabbit lens cortex on a Sephacryl S-200 gel column yielded four beta-crystallin peaks (beta1, beta2, beta3 and beta4), all eluting between alpha and gamma-crystallins. Their molecular weights were estimated to be 250,000, 130,000, 60,000, and 37,000 daltons, respectively. SDS-gradient gel electrophoresis of these beta-crystallins gave rise to characteristic polypeptides; beta1, two polypeptides of 30,000 and 23,000 daltons; beta2, one major polypeptide of 33,000; beta3; two polypeptides of 28,000 and 26,000; and beta4, two polypeptides of 22,500 and 11,200 daltons. From a knowledge of the molecular weights and the ratio of the polypeptides in each crystallin, their oligomeric structure was calculated to be 5:5, 4, 1:1, and 1:1. The relative abundance of these four beta-crystallins was found to be 25.6%, 7.2%, 27.2%, and 2.8% of the total water-soluble proteins of the lens cortex.

Animals↗
PubMed1976

Glutathione and lens epithelial function.

The relationship of the concentration of glutathione (GSH) in lens epithelium to the transport of cations in the lens was studied by decreasing the level of GSH in the epithelium and monitoring subsequent effects in the lens on the distribution of cations, the activity of Na+-K+ ATPase and the uptake and efflux of 86Rb. Oxidation of GSH in cultured rabbit lenses was accomplished by the use of 1 mM tertiary butyl hydroperoxide (TBHP), a reagent which appears to be suitable for the specific oxidation of GSH in this tissue. The concentration of GSH found in the normal lens epithelium was estimated to be 64 mum per gram wet weight or nearly six times that present in the whole lens. A decrease in the concentration of GSH in lens epithelium of 60 per cent or more leads to an increase in hydration, a shift in the distribution of Na+, K+, and Cl-, a decrease in the activity of Na+-K+ ATPase, and a decrease in the active transport, and an increase in the passive diffusion of 86Rb. In the TBHP-treated lenses there is a rapid decrease in the production of lactate, possibly as a result of the inhibition of Na+-K+ ATPase, but the effect on the level of lens ATP is delayed and less pronounced. It appears that the adverse effect on membrane permeability caused by the oxidation of GSH is partially reversed when a high level of GSH returns to the epithelium. However, the decrease in active transport of 86Rb and the inactivation of Na+-K+ ATPase are not reversed by either regeneration of GSH in the tissue or by treatment with exogenous dithiothreitol and may indicate an irreversible conformational change in the enzyme initiated by the loss of the protective effect of GSH. The data indicate that a critical level of GSH is required in the lens epithelium for the maintenance of normal cation transport.

Adenosine Triphosphatases↗
PubMed1975

Evidence for lens oxoprolinase, an enzyme of the gamma-glutamyl cycle.

The presence of oxoprolinase, an enzyme of the gamma-glutamyl cycle, not previously reported in the lens was demonstrated by organ-culture technique and from a study of the partially purified enzyme. The evidence for oxoprolinase in intact rabbit lens is based on the following: (1) [14C]-labeled oxoproline is utilized by the lens giving rise to labeled CO2, (2) [14C]-oxoproline is converted to glutamic acid, which is subsequently incorporated into glutathione, (3) formation of labeled glutamic acid and CO2 from [14C]-oxoproline is effectively blocked by a structural analog of the compound L-2-imidazolidone-4-carboxylic acid, a known inhibitor of oxoprolinase. The enzyme was partially purified from bovine lens capsule epithelium and certain of its properties were examined. Ocular lens was also found to contain significant amounts of oxoproline, an intermediate of the gamma-glutamyl cycle.

Acetylcholine↗