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G de Renzis

Publications and source records attributed to G de Renzis.

10 recordsLinked to original sources
PubMed1996

Calcium-activated chloride currents in primary cultures of rabbit distal convoluted tubule.

Chloride (Cl-) conductances were studied in primary cultures of rabbit distal convoluted tubule (very early distal "bright" convoluted tubule, DCTb) by the whole cell patch-clamp technique. We identified a Cl- current activated by 2 microM extracellular ionomycin. The kinetics of the macroscopic current were time dependent for depolarizing potentials with a slow developing component. The steady state current presented outward rectification, and the ion selectivity sequence was I- > Br- > > Cl > glutamate. The current was inhibited by 0.1 mM 5-nitro-2-(3-phenylpropyl-amino)benzoic acid, 1 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, and 1 mM diphenylamine-2-carboxylate. To identify the location of the Cl- conductance, 6-methoxy-N-(3-sulfopropyl)quinolinium fluorescence experiments were carried out in confluent cultures developed on collagen-coated permeable filters. Cl- removal from the apical solution induced a Cl- efflux that was stimulated by 10 microM forskolin. Forskolin had no effect on the basolateral Cl- permeability Cl- substitution in the basolateral solution induced an efflux stimulated by 2 microM ionomycin or 50 microM extracellular ATP Ionomycin had no effect on the apical Cl- fluxes. Thus cultured DCTb cells exhibit Ca(2+)-activated Cl- channels located in the basolateral membrane. This Cl- permeability was active at a resting membrane potential and could participate in the Cl- reabsorption across the DCTb in control conditions.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1987

Activation of amino acid uptake at fertilization in the sea urchin egg. Requirement for proton compartmentalization during cytosolic alkalosis.

The comparative importance of the release of intracellular ionic calcium, Na+/H+ exchange and cytosolic alkalosis as activator signals was studied on the development of amino acid uptake at fertilization in sea urchin eggs. We show that, once stimulated, the rate of valine uptake is greatly dependent upon intracellular pH. Suppression of the Na+/H+ exchange at the time of activation, by applying ionophore (A23187) in sodium-free artificial sea water (ONaASW), inhibits the development of valine influx. This cannot be restored by a further (30 min later) alkalosis by transferring eggs into sea water. Suppressing the alkalosis in the presence of Na+/H+ exchange at fertilization by simultaneous addition of acid into sea water results in activation of the amino acid carrier which exhibits an increased rate of transport as soon as the eggs are replaced in sea water at pH 8.0. The absence of alkalosis in eggs activated in ONaASW can be counterbalanced either by adding NH4Cl 10 mM or by transfer into ASW at pH 9.0 at activation. Ammonia-treated eggs absorbed amino acid as controls, whereas eggs in sea water at pH 9.0 failed to develop a valine uptake system, suggesting that ammonia can completely replace the effect of Na+/H+ exchange. Furthermore, addition of NH4Cl immediately before fertilization conceals the Na+/H+ exchange but stimulates valine uptake as in controls. These data suggest that: the occurrence of the intracellular calcium increase alone is not sufficient for the develpment of the amino acid transport system; cell alkalinization at fertilization derives from the cytoplasmic membrane-located Na+/H+ exchange and an inward movement of protons into a cortical acidic compartment, which is discussed.

Amino Acids↗
PubMed1980

Cl--HCO3--ATPase in gills of the rainbow trout: evidence for its microsomal localization.

The intracellular localization of a Cl--HCO3--ATPase, which is inhibited by SCN-, was studied in the gills of the rainbow trout, Salmo gairdneri. This activity can be measured in the absence of contamination by mitochondria (i.e., in the absence of succinate dehydrogenase or cytochrome c oxidase activities). The distribution of the 5'-nucleotidase and of the ATPase stimulated by Cl- and HCO3- after sucrose density gradient centrifugation of the microsomal fraction was compared. Because those activities cannot be separated, it is postulated that the anion-stimulated ATPase is located in the plasma membrane. The activation of this microsomal anion ATPase by chloride has been studied extensively. The possible role of the Cl--HCO3--ATPase of trout gills in the Cl-/HCO3- exchange and in the regulation of the internal acid-base balance is discussed.

Adenosine Triphosphatases↗
PubMed1977

A Cl-/HCO-3-ATPase in the gills of Carassius auratus. Its inhibition by thiocyanate.

An ATPase is demonstrated in plasma membrane fractions of goldfish gills. This enzyme is stimulated by Cl- and HCO-3, inhibited by SCN-. Biochemical characterization shows that HCO-3 stimulation (Km = 2.5 mequiv./l) is specifically inhibited in a competitive fashion by SCN- (Ki = 0.25 mequiv./l). This residual Mg2+-dependent activity is weakly affected by SCN-. In the microsomal fraction chloride stimulation of the enzyme occurs in the presence of HCO-3 (Km for chloride = 1 mequiv/l); no stimulation is observed in the absence of HCO-3. Thiocyanate exhibits a mixed type of inhibition (Ki = 0.06 mequiv./l) towards the Cl- stimulation of the enzyme. Bicarbonate-dependent ATPase from the mitochondrial fraction is stimulated by Cl-, but this enzyme has a relatively weak affinity for this substrate (Km = 14 mequiv./l).

Adenosine Triphosphatases↗
PubMed1975

The branchial chloride pump in the goldfish Carassius auratus: relationship between Cl-/HCO3- and Cl-/Cl-- exchanges and the effect of thiocyanate.

1. The effect of thiocyanate on chloride and sodium fluxes across the gill was studied in the goldfish Carassius auratus. At low external chloride concentrations, addition of SCN- to the bathing solution markedly inhibited chloride influx and efflux, the net flux being reversed, SCN- injection was without effect. SCN- had no effect on sodium fluxes when injected or added to the external medium. 2. The inhibition of chloride influx by SCN- was of a mixed type involving simultaneous modifications of the affinity constant of the carrier for Cl- and of the maximal Cl- influx. The affinity constant of the carrier for SCN- was 10 times lower than that for Cl-. 3. The gill of the goldfish was found to be practically impermeable to SCN-. 4. In the presence of external SCN-, the Cl-/HCO3- exchange was reversed: Cl- was lost against HCO3- which is absorbed. This suggests an obligatory exchange. 5. Exchange diffusion for chloride was also demonstrated. 6. A kinetic model is proposed to explain chloride and bicarbonate transport across the gill of Carassius auratus.

Animals↗