Electrical characteristics of isolated Aplysia californica intestine

• 1.1. Transmural potential difference and short-circuit current of intestinal sheets of Aplysia califonica were stable up to 5 hr.
• 2.2. Transmural potential difference was serosa negative relative to the mucosa and the short-circuit current was consistent with a net active anion transport from mucosa to serosa.
• 3.3. Transmural potential difference and short-circuit current were dependent upon the presence of sodium and chloride in the bathing medium.
• 4.4. Transmural potential difference and short-circuit current were predominantly dependent upon aerobic metabolism, however a finite residual electrical component was dependent upon glycolytic energy.
• 5.5. The major portion of the short-circuit current is carried by a net active chloride transfer from the mucosal to serosal compartments while the minor portion is carried by a net active sodium transfer in the same direction.

     

Electrical transport characteristics of Aplysia californica intestinal epithelium

• 1.1. Replacing chloride (Cl⁻) with sulfate (SO₄²⁻) in the bathing medium drastically reduced the mucosal membrane potential difference (ψ_m).
• 2.2. The voltage divider ratio was significantly greater than one.
• 3.3. Mucosal ^d-glucose decreased the input resistance of the intestinal epithelium.
• 4.4. Addition of furosemide to the mucosal bathing medium inhibited transepithelial potential difference and short-circuit current.
• 5.5. Addition of SITS to the mucosal bathing medium partially inhibited transepithelial potential difference and short-circuit current.
• 6.6. Diffusion potentials in the intestinal epithelium were symmetrical.

     

Regulation of amiloride-sensitive Na+ absorption in the lizard (gallotia galloti) colon by aldosterone

• 1.1. Acute (AT) or chronic (CT) administration of exogenous aldosterone brought about a considerable increase in transmural potential difference (PD), short-circuit current (Isc) and net sodium flux (J_net^Na).
• 2.2. A good relationship between Isc and J_m-s^Na was observed in CT but not in AT or UC (untreated controls).
• 3.3. Addition of mucosal amiloride reduced Isc in AT and CT colons, but did not cause any change in UC colons. The relationship between Isc and J_m-s^Na, observed in CT was totally suppressed by the diuretic.
• 4.4. J_net^Na was reduced in AT tissues and abolished in CT colons by amiloride.
• 5.5. The present results strongly suggest that aldosterone levels quantitatively and qualitatively modify sodium absorption across colonie mucosa in a dose-dependent fashion and that lower levels of the hormone are required to induce the electrogenic Na absorption than to suppress the electroneutral transport.

     

Active transport of d-glucose in intestinal segments,in vitro,of the scup,Stenotomus versicolor and the puffer,Spheroides maculatus

• 1.1. Active transport of d-glucose was shown using intestinal sac preparations, in vitro, made from two marine fish, the scup, Stenotomus versicolor and the puffer, Spheroides maculatus.
• 2.2. Differences in absorption characteristics were evident in populations from year to year.
• 3.3. Anaerobiotic conditions, i.e. 100 per cent nitrogen gassing of the incubation medium, inhibit the active transport of d-glucose in scup and puffer intestine.
• 4.4. Phlorizin, 5 × 10⁻⁴ M, inhibits the active transport of d-glucose in scup intestine.
• 5.5. Intestinal transmural glucose transport mechanisms operate well at incubation temperatures, 20°–27°C, i.e. temperatures close to habitat and holding tank temperatures, whereas movement of the sugar against a concentration gradient is interrupted at higher incubation temperatures, 29° and 30°C.
• 6.6. Detailed comparison of procedures and results with those used by other workers in the field of in vitro intestinal absorption of poikilotherms suggests that aerobic metabolism may not be a uniformly significant energy source in intestinal active transport.

     

Intestinal l-methionine transport in the cultured gilthead bream (Sparus aurata)

• 1.1. The influx and transepithelial movements of l-methionine and its effects on the electrophysiology and Na-Cl-transport in upper and lower intestine of the cultured fish, Spanis aurata, were measured.
• 2.2. The K_m and V_max of l-methionine influx into the tissues were higher in lower intestine than in upper intestine. A prominent diffusion-like transport component was also measured in both segments during influx experiments.
• 3.3. Net transepithelial fluxes of l-methionine (1 mM) were observed in both upper and lower intestine, this transport being Na⁺-dependent.
• 4.4. The two intestinal segments exhibited an electrical potential difference (PD) and a short circuit current (I_sc) serosa negative or near zero. Tissue conductance (G_t) was higher in posterior than in lower intestine.
• 5.5. Addition of l-methionine to the mucosal side of lower or upper intestine did not induce changes in PD in either part.
• 6.6. Isotopic fluxes of Cl⁻ or Na⁺ measurements under short circuit conditions showed that there were no net Cl⁻ or Na⁺ transport in either part.
• 7.7. l-Methionine additions to the mucosa did not induce changes in unidirectional fluxes of Cl⁻ or Na⁺ or in the (I_sc) in either the anterior or posterior intestine.

     

Changes in the EEL intestine during seawater adaptation

• 1.1. Rate of fluid absorption by eel (Anguilla rostrata) intestinal sacs in vitro reached seawater adapted values 3 days after transfer from freshwater to seawater.
• 2.2. After 3 days in seawater oxygen consumption and Na-K-ATPase activity of intestinal mucosa had not increased over freshwater values.
• 3.3. The weight of intestinal mucosa increased 32% during seawater adaptation as a result of an increase in the number of mucosal cells (hyperplasia).
• 4.4. The rate of intestinal fluid absorption was reduced by 10⁻⁴ M ouabain and was not affected by 10⁻⁴ M acetazolamide.

     

Kinetic properties of cat liver microsomal glucose-6-phosphatase

• 1.1. Cat liver microsomes contain the multifunctional enzyme glucose-6-phosphatase.
• 2.2. High specificity was shown for the phosphohydrolase as well as for the transferase activity.
• 3.3. Both activities have high V_max values determined in optimized conditions.
• 4.4. The phosphate transfer with carbamyl-phosphate as a phosphoryl donor and d-glucose as acceptor is consistent with a random mechanism in which the binding of one substrate decreases the enzyme's affinity for the second substrate.

     

Effect of caffeine,theophylline and nicotine on d-glucose and folate transport in rat jejunal brush border membrane vesicles

• 1.1. Nicotine at 10 mM, but not caffeine or theophylline, reduced by 20% the overshoot of the Na⁺-dependent d-glucose transport in ratjejunal brush border membrane vesicles.
• 2.2. Since nicotine did not affect the transport of Na⁺, its inhibition on Na⁺-dependent d-glucose transport must be due to a direct effect upon the d-glucose transport system.
• 3.3. Folate transport in these membrane vesicles was found to a be a free diffusion process at pH 7.4.
• 4.4. Neither caffeine, theophylline nor nicotine has any effect on folate transport.

     

Preliminary studies on the characteristics of phenylalanine and β-methyl-glucoside transport in the tench intestine in vitro

• 1.1. The unidirectional transepithelial fluxes of L-phenylalanine, β-methyl-D-glucoside and sodium ions across emusculated sheets of tench mid-intestine were determined in flux chambers.
• 2.2. No net sodium flux was detectable, but phenylalanine was preferentially transferred from the mucosal to the serosal fluid.
• 3.3. There was also a net movement of β-methyl-glucoside towards the serosal medium, but it was much smaller than that of phenylalanine.
• 4.4. This transport was accompanied by an accumulation of each substrate from the mucosal medium into the tissue to a similar level and against a concentration gradient.
• 5.5. The poor transfer of the monosaccharide into the serosal medium could therefore be attributed to a low permeability of the baso-lateral membrane of the enterocyte for this substance.
• 6.6. The influx of L-phenylalanine and of β-methyl-d-glucoside into the epithelial cells of tench midintestine was examined by incubating slices of emusculated intestine in radioactively-labelled solutions of the substrate for 2 min.
• 7.7. The steady-state uptake was assessed after similar incubations lasting 45 min.
• 8.8. Phenylalanine influx obeys the Michaelis-Menten equation with a K_m of 2.9 mM and is dependent on the presence of sodium ions in the incubation medium.
• 9.9. β-Methyl-glucoside influx reveals the same characteristics with a K_m of 2.0 mM but a considerably lower V_max; in addition, it is inhibited by galactose.
• 10.10. The influx of both substrates is reduced by harmaline, which also inhibits the uptake of radioactive sodium by this preparation.
• 11.11. The steady-state uptake of β-methyl-glucoside is also inhibited by ouabain and by 2.4-dinitrophenol.
• 12.12. These results suggest that the mechanisms for sodium-dependent influx of monosaccharides and neutral amino-acids in the tench intestine are similar to those found in mammalian tissues.
• 13.13. The principal difference appears to involve the release of monosaccharides across the baso-lateral membrane of the enterocyte.

     

Na+-independent sugar uptake by rat intestinal and renal brush border and basolateral membrane vesicles

• 1.1. Uptake of [¹⁴C]-labelled d-glucose, l-arabinose and d-fructose by intestinal and renal brush border and basolateral membrane vesicles was studied in the absence of Na⁺ .
• 2.2. The Na⁺-independent d-glucose transport system in these membrane vesicles was saturable, sensitive to phloretin, stereospecific and accessible only to d-glucose and d-galactose.
• 3.3. Na⁺-independent l-arabinose transport was not saturable even when its concentration was raised to 300 mM and it was insensitive to phloretin.
• 4.4. Na⁺-independent d-fructose transport demonstrated saturation kinetics with only renal brush border membrane vesicles, but it was not inhibited by either phloretin or phlorizin.
• 5.5. These studies indicated that the Na⁺-independent carrier-mediated d-glucose/d-galactose transport system of intestinal and renal brush border and basolateral membranes is clearly not shared by other monosaccharides.

     

The effect of myo-inositol on the ability of Ditylenchus dipsaci,D. myceliophagus and Anguina tritici to survive desiccation

• 1.1. The effect of myo-inositol on the ability of three species of nematodes to survive desiccation has been studied.
• 2.2. Survival rates obtained from worms treated with an inositol bathing medium were compared with survival rates of worms treated with distilled or tapwater media.
• 3.3. Highest survival rates were found in those nematodes that were placed in an inositol solution prior to desiccation.
• 4.4. Tapwater facilitated higher revival rates than did distilled water in both D. dipsaci and D. myceliophagous.
• 5.5. No such differences were found for A. tritici.
• 6.6. The results are discussed in relation to the possible mechanisms of protection afforded by the different bathing media.

     

Specificity of the permissive effect of d-Glucose on insulin release in chicken pancreas

• 1.1. As previously shown, 14 mM d-glucose, a non-insulinotropic concentration in isolated chicken pancreas, permits an insulin release in response to d-glyceraldehyde, (d-GA; a glycolytic fuel) and l-leucine or α-ketoisocaproic acid (α-KIC) (non-glycolytic fuels), which alone are not initiators of insulin release in this species.
• 2.2. The “permissive” effect of d-glucose was also observed in the presence of d-mannose (which, as shown herein, is not insulinotropic alone).
• 3.3. The specificity of glucose for this “permissive” effect was, therefore, subsequently questioned in the presence of 10mM α-KIC by substituting various glycolytic and non-glycolytic fuels to glucose.
• 4.4. d-GA (at 5 and 15mM), d-mannose (30 and 50 mM), or the association of l-glutamine + l-asparagine permitted an insulin release in response to α-KIC.
• 5.5. The response was, however, delayed with d-GA, only occasionally with 50 mM d-mannose, and required high concentrations and was delayed in the presence of l-glutamine + l-asparagine as compared to that obtained with 14mM d-glucose + α-KIC.
• 6.6. In conclusion, the threshold of fuel-induced insulin release is much higher in the chicken than in mammals and this threshold is most efficiently lowered by glucose.

     

The effects of chronic metabolic acidosis on patterns of protein synthesis in rat renal cortex

• 1.1. In the rat chronic metabolic acidosis increases the net synthesis of 17 renal cortex proteins by amounts ranging from 1.5 to 4.5-fold.
• 2.2. These proteins have molecular weights between 13,000 and 42,000 and isoelectric points between approximately 5.5 and 7.0.
• 3.3. No new proteins not also present in normal animals are detected in renal cortex samples from acidotic animals.
• 4.4. Three proteins undergo substantial reductions in their net synthetic rates in chronic metabolic acidosis.
• 5.5. On the basis of their physical properties and similar alterations in net synthetic rate in acidosis some of these proteins appear to be closely related and may be coordinately expressed in the rat kidney.

     

Interaction of ligands in phosphorylase A as monitored by crosslinking and enzymatic modifications: Synergism of glucose and caffeine manifested in the exposure of N-terminal segment

• 1.1. Glycogen, caffeine and glucose dissociate phosphorylase a tetramer to dimers with half-maximum effect at 0.16%, 1.1 and 71 mM concentration, respectively, as monitored by crosslinking with dimethyl suberimidate at 18°C.
• 2.2. The above ligands increase the rate of dephosphorylation and tryptic digestion of phosphorylase a at 18°C in the same way with half-maximum effect at 0.04%, 0.1 and 9 mM concentration, respectively.
• 3.3. Caffeine and glucose acted synergistically in tetramer dissociation as well as in the enzymic modifications.
• 4.4. The α-anomer of d-glucose was twice as effective as its mutarotational equilibrium solution.

     

Enzymes of fructose metabolism in the intestinal mucosa of the rat (Rattus norvegicus). Localization along the small intestine; consequences of dietary fructose

• 1.1. The activities of all the eight enzymes of conversion of fructose to glucose, of all the three key enzymes of glycolysis and of the two dehydrogenases of pentose shunt were determined in proximal and distal mucosa of small intestine.
• 2.2. With the exception of hexokinase, all of these enzymes have an activity significantly higher in the proximal than distal mucosa.
• 3.3. The gradient along the intestine is particularly important for the three enzymes which are typical for fructose metabolism (ketohexokinase, triokinase and fructose-1-phosphate aldolase), for glucose-6-phosphatase and for phosphofructokinase.
• 4.4. The effects of fructose diet on the enzyme activities are compatible with the results, described in other papers, concerning the final products of metabolism.
• 5.5. The increase of fructose metabolism appears to result mainly from the stimulation of the activities of ketohexokinase and fructose-1-phosphate aldolase which control all the pathways of ketohexose utilization.
• 6.6. The activation of glucose-6-phosphatase, in comparison with the other enzymes which are involved in glucose-6-phosphate metabolism, explains the appearance of the ability to synthesize glucose with fructose as substrate. This enzyme is the only key enzyme of fructose to glucose conversion which responds to fructose feeding in distal mucosa.
• 7.7. The activities of hexokinase and phosphofructokinase are not increased by fructose feeding.
• 8.8. The activity of pyruvate kinase. the only key glycolytic enzyme which is necessarily implicated when fructose is the substrate, is stimulated but less than the typical enzymes of fructose metabolism.
• 9.9. But, because of its quantitative importance, the glycolytic pathway is responsible for the most part of the observed increase of fructose utilization.
• 10.10. The responses of pyruvate kinase, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities to fructose feeding are similar in the two parts of small intestine.
• 11.11. The activities of ketohexokinase, triokinase and glucose-6-phosphate isomerase are stimulated only in the proximal small intestine mucosa.
• 12.12. The other enzyme activities which are stimulated in proximal segment are also increased in distal segment.
• 13.13. All segments of small bowel show adaptive changes to dietary manipulation but not necessarily for all their functions.
• 14.14. The gradient of enzyme activities from the proximal to the distal small intestine persists despite dietary modification, but the data do not determine that this gradient is intrinsic or that it is not intrinsic.

     

Changes in chemical composition of muscle in young hybrids between russian sturgeon Acipenser guldenstadti brandt × beluga Huso huso l. (Pisces; acipenseriformes) under different levels of salinity

• 1.1. The salinity tolerance in young RS × B hybrids increases as the fingerlings grow. The specimens weighing about 7 g are able to tolerate the direct transfer to the water salinity 18%..
• 2.2. Under hypo- and iso-osmotic water ion concentration in the hybrid muscle free amino acids, the exchange of taurine for β-alanine and glycine takes place.
• 3.3. Under hyperosmotic conditions within the first 2 days in the hybrid muscle the water quantity declines, the protein quantity also slightly decreases, the urea and free amino acids concentration (mostly alanine, aspartic and glutamic acids, leucine), and a portion of reserved lipids increase.
• 4.4. During the next 4 days the muscle moisture, protein quantity, and the concentration of urea and free amino acids return to control values, but the portion of reserved lipids declines below the original level.

     

Effects of photoperiod on sodium flux in Corbicula fluminea (Mollusca:Bivalvia)

• 1.1. A significant diurnal rhythm of net sodium flux was demonstrated in the freshwater clam Corbicula fluminea entrained to either a 12L:12D or 24L photoperiod.
• 2.2. Highest net flux occurred during the dark hours on 12L: 12D. The overall mean net flux over 24 hr was not significantly different from a steady state condition.
• 3.3. Net flux values of clams on a 24L photoperiod were negative and significantly lower than the net flux on a 12L:12D photoperiod.
• 4.4. The 12L: 12D net sodium flux rhythm pattern is similar to rhythmic patterns of other physiological processes in another freshwater clam.

     

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Coupling of acetylcholinesterase to activated nylon nets

• 1.1. Three methods for the activation of nylon net and the coupling of acetylcholinesterase to the activated nylon nets are described.
• 2.2. Activation of nylon net was brought about by (a) O-phosphorylation with phosphoryl chloride; (b) O-alkylation with dimethyl sulfate and (c) hydrolytic cleavage with hydrochloric acid.
• 3.3. Kinetic studies indicated that reactions catalyzed by nylon-net enzyme derivatives are substantially controlled by diffusional supply of substrate. The value of K_m were 3–13 fold higher than the soluble enzyme.
• 4.4. Enzyme molecules appeared to have covered the entire net uniformly.
• 5.5. Introduction of spacer between the nylon net and the enzyme molecules significantly increases the half lives of nylon-net enzyme derivatives.

     

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