Biological effects of heavy metals: an overview.

Heavy metals constitute a very heterogeneous group of elements widely varied in their chemical properties and biological functions. Heavy metals are kept under environmental pollutant category due to their toxic effects on plants, animals and human being. Heavy metal contamination of soil results from anthropogenic as well as natural activities. Anthropogenic activities such as mining, smelting operation and agriculture have locally increased the levels of heavy metals such as Cd, Co, Cr, Pb, As and Ni in soil up to dangerous levels. Heavy metals are persistent in nature, therefore get accumulated in soils and plants. Heavy metals interfere with physiological activities of plants such as photosynthesis, gaseous exchange and nutrient absorption, and cause reductions in plant growth, dry matter accumulation and yield. Heavy metals also interfere with the levels of antioxidants in plants, and reduce the nutritive value of the produce. Dietary intake of many heavy metals through consumption of plants has long term detrimental effects on human health.

Changes in tubular membrane glycosylation in diabetic, insulin and thyroxin treated rat kidneys.

The effect of insulin, thyroxine and alloxan induced diabetes has been studied on brush border membrane glycosylation in rat kidneys. Expressed on dry weight basis, the membrane protein was elevated in insulin, thyroxine and diabetic membranes compared to the control group. Sialic acid content of the membranes was significantly reduced in insulin and thyroxine injected animals whereas fucose level was unaffected under these conditions. Brush border fucose content was significantly reduced in diabetic animals but sialic acid content was unaffected. Membrane hexose and hexosamines levels were unaltered by hormone treatments, but in diabetic rats hexosamine level was significantly reduced. The binding of radiolabelled UEA, WGA, PNA to purified brush borders corroborated changes in membrane saccharides. These findings suggest the role of hormones in membrane glycosylation of rat kidney tubules.

Molecular and physicochemical aspects of local anesthetic-membrane interaction

Local anesthesia is achieved by the binding of anesthetic molecules to the sodium channel, a membrane protein responsible for the transport of the extracellular sodium to the cytosol. Local anesthetics (LA) bind to the sodium channel inhibiting sodium transport and, as a consequence, the action potential responsible for the nervous impulse. Most LA are relatively hydrophobic ionizable amines that undergo partitioning into lipid. Both activity and toxicity correlate positively with LA hydrophobicity. Effects of LA on the structural and dynamical properties of the membranes lipid region may be responsible for some of the toxic effects caused by these molecules. The present review focuses on research done on the interaction between both the charged and uncharged forms of LA and lipid systems - bilayers and micelles. LA have been found to alter phospholipid gel to liquid crystal phase transition temperature (Tc), to affect bilayer permeability, to influence molecular packing, and to inhibit the bilayer to hexagonal phase transition. Anesthetics in micellized form disrupt bilayers giving rise to lipid-LA mixed micelle-like aggregates. The question of LA location in the bilayer is also addressed. Special emphasis is placed on work focusing on the quantitative analysis of drug binding, as well as on the effects of binding on physicochemical properties of the LA, such as extent of ionization (pK shifts) and rates of chemical reactions. The understanding of these phenomena has contributed to the development of less toxic liposomal formulations capable of prolonging the duration of anesthesia.

Vitamin E protects intestinal basolateral membrane from CMF-induced damages in rat.

CMF is a combination of anticancer chemotherapeutic agents Cyclophosphamide, Methotrexate and 5-Fluorouracil. Vitamin E protects the basolateral membrane (BSM) from CMF induced lipid peroxidative damages. Rats were treated intravenously with cyclophosphamide-10 mg, methotrexate-1.0 mg and 5-fluorouracil-10 mg per kg body weight for six cycles. Vitamin E (600 mg/kg body weight) was administered orally, daily. Intestinal basolateral membrane bound ATPases (3.6.1.3), Alkalinephosphatase (3.1.1) and 5'-Nucleotidase (3.1.3.5) were protected by co-administration of vitamin E with CMF. In CMF treated rats the lipid peroxidation levels were found to be elevated with a significant depletion in membrane sulfhydryl groups. In vitamin E co-administered animals, the enzyme activities were found to be restored with concomitant reduction in malondialdehyde levels and an increase in the sulfhydryl groups. The membrane cholesterol and phospholipid levels which were altered in CMF treated rats were bought back to the normal in co-administration of vitamin E.

Effect of calcium ion on Hydrilla verticillata thylakoid membrane O2 evolution.

Calcium ion-dependent reactivation of O2 evolution activity has been investigated in Hydrilla verticillata thylakoid preparations. Washing the thylakoids in calcium-free buffer or calcium-free buffer containing 1.5 M NaCl or 1.5 M NaCl plus 20% methanol, reversibly inhibited O2 evolution activity. The activity was restored on addition of calcium as calcium chloride and partially by strontium chloride. Immobilization of thylakoids with glutaraldehyde (GA) arrested the loss in O2 evolution activity caused by calcium-free high salt washing. However, calcium sensitivity was discernible in GA immobilized thylakoids subjected to calcium-free high salt washing. Since glutaraldehyde checks the loss of extrinsic thylakoid polypeptides due to washing, it is assumed that the calcium ion has regulatory functions in the photosynthetic electron transport, besides its interaction with thylakoid proteins.

Efecto del etanol sobre las membranas biológicas / Effects of ethanol on the biological membrans

El etanol al igual que otros alcoholes puede actuar en las membranas biológicas fundamentalmente de 3 formas: 1). alterando la fluidez de las membranas, lo que indirectamente afectaría el funcionamiento de las proteínas como enzimas y canales;2)produciendo una deshidratación a nivel de las membranas;3)interactuando directamente con las proteínas de la membrana. Los efectos del etanol en las membranas biológicas podrían explicar en parte, los efectos generalizados del etanol