Giuseppe Cassano

Na+/H+ exchange in the kidneys of eels (Anguilla anguilla) adapted to sea water or to freshwater environments: Studies with brush border membrane vesicles

Abstract 1. 1. In brush border membrane vesicles isolated from eel kidneys, adapted either to sea water or freshwater environments, a Na+/H+ antiporter is present. 2. 2. Using a calibration plot it is possible to evaluate the amount of protons that this antiporter can accumulate inside the vesicular space. 3. 3. The activity of the antiporter seems to be affected by the salinity of the water; it is higher in animals adapted to seawater. 4. 4. This adaptation seems to occur by a Jmax regulation of the antiporter.

Effects of membrane potential on Na cotransports in eel intestinal brush-border membrane vesicles: studies with a fluorescent dye

SummaryThe Na-dependent transport of a number of organic molecules (d-glucose,l-proline,l-alanine,l-phenylalanine) in brush-border membrane vesicles isolated from the intestine of the eel (Anguilla anguilla) was monitored by recording the fluorescence quenching of the voltage-sensitive cyanine dye 3,3′-diethylthiacarbocyanine iodide (DiS-C2(5)). The experimental approach consisted of: a) generating an inside-negative membrane potential mimicking “in vivo” conditions: b) measuring the rate of membrane potential decay (i.e., the rate of fluorescence quenching decay) due to Na-neutral substrate cotransport. Rates of membrane potential decay showed saturation on substrate concentration andKapp values (the substrate concentration giving 50% of the maximal rate) were estimated for Na-dependent transport ofd-glucose (0,099mm),l-alanine (0.516mm),l-proline (0.118mm) andl-phenylalanine (2.04mm). The influence of an inside-negative membrane potential on the affinity of the transporter for glucose and for sodium is discussed.

How many Na+-dependent carriers for l-alanine and l-proline in the eel intestine? Studies with brush-border membrane vesicles

Using brush-border membrane (BBM) vesicles prepared from the intestine of the European eel, the specificity of L-alanine and L-proline Na+-dependent transport was investigated by measuring the uptake of isotopically labelled substrates. In the presence of Na+ ions, cross-inhibition between alanine and proline transports was observed; in addition alpha-(methylamino)isobutyric acid (MeAIB) inhibited proline but had no effect on alanine uptake. These results can be explained by the presence, in eel intestinal BBM vesicles, of at least two distinct agencies for Na+-dependent proline and alanine translocation. The first system is specific for alanine and short-chain neutral amino acids; the second system, specific for imino acids and the N-methylated analogues, is regulated by alanine concentration.

Basolateral amino acid and glucose transport by the intestine of the teleost, Anguilla anguilla.

1. D-glucose transport into BLMV was osmotically reactive, sodium independent, and inhibited by phloretin but not by phloridzin. 2. The survey of 6 L-amino acids identified three groups with respect to transfer across the basolateral cell border. Transport of proline and glutamate occurred by Na-dependent carriers and by apparent simple diffusion. Alanine, lysine and phenylalanine were transported by Na-independent carriers and apparent simple diffusion. Glycine transport was stimulated above apparent simple diffusion only by a simultaneous inwardly-directed Na gradient and outwardly-directed K gradient. 3. Only proline and glutamate demonstrated the ability to depolarize the membrane potential, consistent with Na-dependent rheogenic transport.

Do neutral amino acids and their N-methylated analogues share the same Na-dependent carrier in brush-border membrane from the eel intestine?

Abstract 1. 1. Kinetics of Na-neutral amino acid cotransport by brush-border membrane vesicles from the eel ( Anguilla anguilla ) intestine was studied. 2. 2. The substrate-dependent Na-influx was estimated by monitoring the decay of a preset inside negative membrane potential with a voltage-sensitive fluorescent dye. 3. 3. N-Methylglycine, N-methylalanine and α-(methylamino)-isobutyric acid are transported by the Na-dependent carrier responsible for proline translocation. This carrier is distinct from the one responsible for glycine, alanine and α-aminoisobutyric acid translocation.