Biomedical subjects
A K Charles
Publications and source records attributed to A K Charles.
Histopathological changes in venous grafts and in varicose and non-varicose veins.
AIMS: To examine veins histologically from different sites in the body to study the effect of venous pressure; and to examine veins used as aortocoronary grafts. METHODS: The axillary vein, femoral vein at the inguinal ligament, the short saphenous vein at the knee and the long saphenous vein at the ankle were removed from 24 necropsy cases of patients aged 2 months to 80 years. Fifteen varicose saphenous veins and 12 aortocoronary grafts removed at surgery were obtained. All were examined histologically. RESULTS: Varying degrees of intimal thickening composed of collagen, elastin, and smooth muscle were found. These changes were most noticeable in the varicose veins. Intimal changes were also seen related to valves and to adjacent arteries. No clinically relevant lipid was seen in the native veins, though atheromatous changes were seen in the grafts. CONCLUSIONS: Venous changes are related to venous pressure, to local haemodynamic effects, and probably to hypoxia. The changes are often focal and seem to be sequential in their formation. True atheroma is seen in the aortocoronary grafts but is not seen in native veins and this may be the result of additional factors.
Regional mirex distribution and its effects on gamma-aminobutyric acid and flunitrazepam binding in mouse brains.
Following ip injection of [14C]mirex, its regional distribution was studied parallel to its in vitro effects on [3H]-gamma-aminobutyric acid (GABA) and [3H]flunitrazepam (FNZ) binding to, and [3H]GABA release from, synaptosomes of various mouse brain regions, in order to determine the relationship between relative mirex distribution and its neurotoxic effects mediated through the GABA receptor-ionophore complex. The pattern of mirex uptake into cerebral cortex (CC), brainstem (BS), and cerebellum (CB) showed an initial linear dose-dependent uptake, followed by a decline at higher concentration. The Vmax and Km values determined for the linear mirex uptake phase indicated varied affinities by brain regions, CB and BS being more susceptible to mirex uptake than CC. Both synaptosomal GABA binding and FNZ binding were significantly reduced by mirex in the order of BS approximately equal to CB greater than CC for GABA, and BS approximately equal to CC greater than CB for FNZ. However, mirex lacked any significant effect on the Ca2+-dependent, K+-stimulated release of GABA from radio-prelabeled synaptosomes. While the data indicate no significant differences between brain regions in mirex uptake, they suggest that regional specificities do exist with respect to the inhibition caused by mirex on GABA and FNZ binding to synaptosomes. Unlike the major effects of chlordecone (an analog of mirex) on the dopaminergic system, mirex seems to be primarily neurotoxic through its more specific interaction with the GABA and FNZ binding sites.
Pipecolic acid receptors in rat cerebral cortex.
Identification of [14C]pipecolic acid (PA) receptors was attempted in the solubilized membrane fraction from rat cerebral cortex. Specific binding proteins for both PA and muscimol, a potent gamma-aminobutyric acid (GABA) agonist, were detected in the same preparation. Separation of labeled PA and GABA binding proteins by glycerol gradient centrifugation has shown labeled protein bands of similar sedimentation rates, suggesting that PA and GABA may be binding to identical proteins. It seems likely that the PA binding receptor either may possess the same sedimentation characteristics as that of the GABA receptor, or both GABA and PA which is an endogenous and weak GABA agonist may bind to the same receptor complex, if not to the same binding site.
In vitro effects of cadmium chloride on preimplantation rat embryos.
Preimplantation rat embryos (8-cell, morulae, blastocysts) were incubated for 24 hr in vitro in a Brinster medium with or without cadmium chloride (1 microgram/ml). CdCl2 arrested the development of both the 8-cell and morulae into blastocysts. Morphologic observations revealed the 8-cell embryo to have shrunken cells and pyknotic nuclei. Morulae appeared smaller in size with fewer cells than comparable controls. CdCl2 was clearly cytotoxic to the early blastocysts, inner mass cells were most damaged with cell death, pyknosis, and accumulation of debris.
In vitro binding of mirex by mouse hepatocytes.
Mirex (dodecachlorooctahydro-1,3,4-metheno-2H-cyclobuta[cd]+ ++pentalene) is a hepatic tumorigen that is shown to cause marked disturbances in hepatic cell ploidy in rodents. Kinetic measurements of [14C]mirex binding were performed in freshly prepared diploid (DP) and polyploid (PP) hepatocytes, as well as in erythrocytes, under controlled conditions. The binding of mirex to hepatocytes, irrespective of their ploidy, was partially Na+-dependent and totally Ca2+-independent. Variations in temperature and pH appeared to significantly inhibit mirex binding; the optimum binding was seen at 37 degrees C under physiological pH. The saturation kinetic data revealed that PP cells were saturated at a very low concentration of mirex (two- to threefold) compared to DP, exhibiting a high-affinity binding of mirex to PP with a low Km (347 nM) and Vmax (102 nmol/mg X min). The Km (550 nM) and Vmax (340 nmol/mg X min) values determined for DP cells were of higher magnitude, like those of erythrocytes (Km, 819 nM; Vmax, 330 nmol/mg X min), indicating that distinct differences exist in the binding affinities of three cell types. However, erythrocytes and DP cells showed close similarity in their Vmax values. Interestingly, mirex levels in the lipid compartments of DP and PP cells revealed no apparent differences. The results are discussed in terms of the possible susceptibility of PP cells and their role in the initiation of toxic response leading to hepatotumorigenesis in rodents.
Uptake and disposition of mirex in hepatocytes and subcellular fractions in CD1 mouse liver.
In vivo uptake and disposition of [14C]mirex by CD1 mouse liver subcellular fractions and cells of different nuclear ploidy were examined following single or multiple doses of mirex injected intraperitoneally. Significant amounts of mirex were rapidly taken up by liver (21-29%), suggesting that liver is one of the primary sites of accumulation of the chemical. Among subcellular fractions, mirex was predominantly distributed in mitochondria and microsomes in the irreversibly bound form (about 20%), although its levels fluctuated considerably with time. Mirex was completely dissociated with trichloroacetic acid treatment from both nuclear and plasma membrane fractions, although the total uptake by these fractions was markedly high. The time course of uptake and concentration-dependent disposition of mirex revealed that polyploid hepatocytes selectively accumulated higher amounts of the chemical (two to three times) compared to diploid hepatocytes. The increased affinity of polyploid cells to mirex may indicate a greater susceptibility of this cell type to the chemical insult and also may suggest a possible early involvement of polyploids in the tumorigenic process in rodent livers.
Comparative changes in rat liver cytosolic proteins by mirex, diethylnitrosamine, and dimethylnitrosamine exposure.
Using a newborn rat model for carcinogenesis, changes in liver cytosolic proteins at three stages of tumorigenesis, on Days 21, 97, and 120, by mirex (dodecachloropentacyclo-1,3,4-metheno-2H-cyclobuta[cd] pentalene), and diethyl- and dimethylnitrosamines (DEN and DMN) were studied. Following multiple exposure to the hepatocarcinogens, groups of weanling rats were given dietary phenobarbital (PB) up to 120 days. SDS-PAGE separation of cytosolic proteins showed that at 21 days, prior to PB, two proteins of 26K and 23K mol wt were significantly induced by mirex and DMN while a high mol wt 63K protein was induced only by DEN and DMN. During the period of PB treatment up to 97 days, these proteins were well sustained at a higher level. A marked increase in 21K protein band was also observed at this point. In tumor tissues obtained from DEN and DMN rats continued on PB diet for 120 days, the high level of 63K protein was seen only in DEN and not in DMN tumor. The tumors also showed a significant reduction in 25K protein compared to 21- and 97-day groups. The presence of even lower mol wt proteins of 14-21K was seen in tumors. The early detection and further characterization of these low mol wt proteins may provide clues as to whether they are preneoplastic markers or oncogene products as speculated by other investigators. Moreover, certain similarities in the induction of cytosolic proteins by "epigenetic" and "genotoxic" carcinogens raise more interesting questions regarding the mechanisms of action of these distinct classes of carcinogens.
Effect of D- and L-alpha-aminoadipate on the efflux of L-aspartate, L-glutamate and gamma-aminobutyrate from superfused rat brain slices.
D-alpha-Aminoadipate (D-AA) and L-alpha-aminoadipate (L-AA) were found to significantly reduce spontaneous efflux of [14C]L-aspartate from preloaded rat brain slices. Only D-AA significantly reduced spontaneous efflux of [14C]L-glutamate and [3H]gamma-aminobutyric acid (GABA); L-AA reduced but not significantly the efflux of these 2 labeled amino acids. D-AA reduced K+-stimulated release of [14C]L-aspartate and [14C]L-glutamate significantly, and L-AA that of [3H]GABA significantly. Since both D-AA and L-AA inhibit the uptake of L-aspartate, L-glutamate and GABA, their effects on the efflux of these amino acids are more specific. These results also suggest that it is unlikely that the depressant effect of D-AA, and the excitant effect of L-AA on neurons when applied locally by iontophoresis are secondary to the accelerated or decelerated release of more specific transmitter amino acids from neighboring cells.
Blood-brain barrier transport of L-pipecolic acid in various rat brain regions.
Blood-brain barrier transport of L-[1-14C]pipecolic acid was studied in the ray by single intracarotid injection using 3H2O as a diffusible internal standard. Brain uptake index (BUI) for L-[14C]pipecolic acid (0.036 mM) was found to be 18.1, 10.5, and 12.6 for the cerebral cortex, brain stem, and cerebellum, respectively which was substantially higher than that reported for its analog L-proline in the whole brain. Influx of L-pipecolic acid into the brain was concentration dependent and differed significantly between the cerebral cortex and the brain stem, and between the cerebral cortex and the cerebellum, but not between the brain stem and the cerebellum. Kinetic study of L-pipecolic acid influx revealed a low- and a high-capacity uptake mechanisms. The low-capacity saturable component has Km values ranging from 38 to 73 microM, and Vmax values ranging from 10 to 13 nmol/g/min for the three brain regions. The nonsaturable component has a Km of 4 mM, a Vmax of 200 nmol/g/min and similar diffusion constant (Kd) (0.03 to 0.06 mlg-1 min-1) for all three brain regions. A possible role of the two-component brain uptake mechanism in the regulation of the neuronal function of L-pipecolic acid was suggested.
Assay of delta 1-piperideine-2-carboxylate and synthesis of L-[14C]pipecolate from DL-[14C]pipecolate.
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Effects on muscle of a toxin from Indian cobra (Naja naja naja) venom.
The mode of action of a purified toxin from Naja naja naja (Indian cobra) venom was investigated in frog rectus abdominis muscle, chick biventer cervicis muscle, cat tibialis anterior muscle (close-arterial) and in both innervated and denervated rat diaphragm muscle preparations. The toxin inhibited the acetylcholine responses of rectus abdominis muscle. The inhibition was antagonized by neostigmine and increasing concentrations of acetylcholine, suggesting a competitive binding of the toxin to cholinergic receptors. The toxin, even at high doses, did not produce depolarizing contractures in chronically denervated diaphragm, biventer cervicis muscle and rectus muscle preparations. In both cat tibialis anterior and denervated diaphragm muscles, the toxin abolished the acetylcholine sensitivity of the muscles at a faster rate than its effects on muscle contraction, suggesting a preferred action on the motor end-plate. A well-maintained tetanic contraction and very poor post-tetanic potentiation was observed in all preparations treated with toxin, indicating an atypical Wedensky inhibition. Anti-curare agents, such as K+ and Ca2+, were ineffective in antagonizing the curare-like neuromuscular block in phrenic nerve-diaphragm preparations. A frequency-independent neuromuscular block observed in these nerve-muscle preparations was suggestive of the absence of a possible presynaptic effect. These results demonstrate that although the neurotoxin in some cases can imitate d-tubocurarine, its neuromuscular blocking activity is different from that of curare in many respects.
Metabolism and uptake of L-pipecolic acid by brain and heart.
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Biochemical characterization of a toxin from Indian cobra (Naja naja naja) venom.
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Peripheral versus central action of a toxin from Indian cobra (Naja naja Naja) venom.
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Source of carbohydrate in a toxic protein from Indian cobra (Naja naja naja) venom.
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Uptake, release, and metabolism of D- and L-alpha-aminoadipate by rat cerebral cortex.
Accumulation of L-alpha-aminoadipate by rat cerebral cortical slices is a stereospecific and Na+-dependent process. The uptake of this compound is also temperature-dependent, with a Km of 1.6 X 10(-4)M for the high-affinity system. D-alpha-Aminoadipate has characteristics similar to those displayed by the L-isomer but to a lesser degree. L-Glutamate and L-aspartate inhibit the uptake of L-alpha-aminoadipate. D- and L-alpha-Aminoadipate are, respectively, weak uncompetitive and weak competitive inhibitors for the uptake of L-glutamate and L-aspartate. Both enantiomers inhibit GABA uptake but in quite different ways. The release of L-alpha-aminoadipate from the cerebral cortical slices is stimulated by a high concentration of K+ ions in the presence of Ca2+ in the perfusion buffer; the D-isomer displays this property to a lesser degree. The omission of Ca2+ markedly reduces the release of these two compounds. Less than 10% of the preloaded D- and L-alpha-aminoadipate are metabolized by the cerebral cortex during 40 min of superfusion. The possibility of L-alpha-aminoadipate as a neurotransmitter candidate is discussed.
Lung lipids in experimental emphysema.
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