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Biomedical subjects

M Parisi

Publications and source records attributed to M Parisi.

At least 91 records · Page 5Linked to original sources
PubMed1979

Simultaneous minute by minute determination of unidirectional and net water fluxes in frog urinary bladder. A reexamination of the two barriers in series hypothesis.

Unidirectional and net water fluxes were simultaneously estimated in frog urinary bladder. The minute by minute tritiated water (3HOH) transepithelial flux and the net volume of fluid traversing the tissue were employed. It was observed that: (1) the time course of the increase in the 3HOH flux induced by antidiuretic hormone had a very similar pattern to that reported for the increase in the net movement. (2) Unstirred layers strongly affected the magnitude of the antidiuretic hormone-induced increase in 3HOH fluxes while the time course of the response was almost non-affected. In non-stimulated bladders 3HOH fluxes were poorly modified by medium stirring. New steady-state conditions for 3HOH fluxes were established 1 min after stirring rate modifications. (3) The simultaneously determined net water flux was not affected by a modification in the unstirred layers, indicating that the variations in the measured net water fluxes are a good estimation of the changes in the mucosal border permeability. (4) The presence of an osmotic gradient during hormonal challenge (implying net water fluxes, cell swelling and dilation of the intracellular spaces) did not modify the time course of 3HOH movements. These results suggest that the time course of the increase in water permeability is an intrinsic characteristic of the experimental system that could result from the addition of permeability units that increase in number during the development of the hormonal action.

Animals↗
PubMed1979

Influence of mucosal and serosal pH on antidiuretic action in frog urinary bladder.

Mucosal acidification to pH 6.5 reduced by 88% the oxytocin- (2.2 x 10(-8) M) elicited increase of water permeability in frog urinary bladder. Mucosal alkalinization (pH 10.5) increased by as much as 200% the response to the same concentration of oxytocin. These effects were not observed when supramaximal concentrations of oxytocin were imployed. Similar changes were found when the serosal pH was modified. The hydrosmotic responses elicited by serosal hypertonicity or cyclic AMP plus theophylline were also affected by mucosal or serosal changes of the hydrogen in concentration, suggesting an effect at a post-cyclic AMP level. Important interactions were found between luminal pH and serosal hypertonicity when experimental conditions were employed similar to those observed in the collecting duct of mammalian nephron. Freeze-fracture studies showed that the number of intramembranous aggregates of particles induced by ADH in the luminal membrane was reduced by mucosal acidification and augmented by an increase in medium pH.

Animals↗
PubMed1977

Urea uptake and translocation in toad urinary bladder: the effect of antidiuretic hormone.

The uptake of C14-urea into everted and noneverted bladder sacs was compared, over short time periods (up to 2 min), with the transepithelial urea fluxes. This method allowed the study of the time course of urea uptake and distribution, while previously this problem was only studied in steady-state conditions. When mucosal uptake was studied no accumulation of C14-urea inside the tissue was observed, indicating that the mucosal border could be the limiting step. Comparative studies of urea and inulin uptake from the serosal side showed that urea equilibrated with the water epithelial cells in less than 30 sec. This accumulation suggested again that the mucosal border is an effective barrier for urea translocation. The kinetics of the increase in urea permeability induced by antidiuretic hormone was also studied and it was similar (T1/2:4.3 min) to the kinetics of the increase in water permeability induced by the hormone (T1/2:5.6 min). A strong parallelism was also observed between the time course of the increases in water and urea permeabilities induced by medium hypertonicity (T1/2 25 and 26 min, respectively). The values obtained for the permeability coefficient ktrans), either at rest or under ADH were similar to those previously reported employing steady-state techniques (28+/-8 and 432+/-25 cm-sec-1-10(-7), respectively).

Animals↗
PubMed1976

Water permeability and lipid composition of toad urinary bladder: the influence of temperature.

The water diffusional permeability, its activation energy and the lipid composition were studied in urinary bladders from toads adapted to different temperatures. It was observed that the unidirectional water flux greatly depends on the temperature at which the experiments are performed. This dependence is greater in the animals adapted to higher temperatures. Toads adapted to cold show strong reduction in the activation energy for water diffusion permeability (from 11.4+/-1.9 kcal-mol-1 to 4.4+/-1.1kcal-mol-1) and an increase of 30% in the amount of total lipids from bladder epithelial cells. There were no significant changes in the phospholipid/cholesterol ratio, composition of the parafinic chains or protein concentration between toads adapted to both temperatures. The possibility that water translocates through the mucosal border of the toad bladder by partitioning in the polar zone and diffusioning between the hydrocarbon chains of the membrane lipids and that cold adaptation would induce a stronger "packing" of lipids in the membrane is discussed.

Acclimatization↗
PubMed1973

The effect of hypertonic media on water permeability of frog urinary bladder. Inhibition by catecholamines and prostaglandin E 1 .

The frog urinary bladder undergoes, in some conditions, a marked increase of its water permeability when incubated in hypertonic media. This increase was observed with various nonpermeant solutes. It seems to result from the shrinkage of an osmo-sensitive compartment of the tissue, probably the epithelial cells. Many similarities were found between this effect and the physiological increase in water permeability (hydrosmotic response) elicited by antidiuretic hormone (ADH): both were dependent on the physiological state of the animals, and although the response was slower after hyperosmolar than after hormonal challenge, the patterns of response were similar, and in both cases markedly dependent on bathing solution temperature. Norepinephrine and prostaglandin E(1), which in this tissue reduce the hydrosmotic action of ADH, presumably by inhibiting the adenyl cylase also reduced the effect of hyperosmolarity. Conversely this effect was potentiated by incubation in the presence of oxytocin, exogenous cyclic AMP, and theophylline, conditions in which the intracellular concentration of cyclic AMP is increased. These data demonstrate that the response to hyperosmolarity is elicited, at least partly, by mechanisms also involved in the physiological hydrosmotic response to ADH.

Animals↗
PubMed1972

Conductance properties of artificial lipidic membranes containing a proteolipid from Electrophorus. Response to cholinergic agents.

Previous studies have shown that a special proteolipid extract from the electric organ of Electrophorus showed high affinity binding for acetylcholine and other cholinergic agents. This proteolipid has now been incorporated into ultrathin lipidic membranes, and the membrane resistance was studied. The resistance decreased from 7.27 +/- 0.82 x 10(5) ohm cm(2) in the control membrane to 1.83 x 10(5) ohm cm(2) with addition of 72 microg/ml proteolipid. The decrease in resistance followed a potential function of order four with the proteolipid concentration in the membrane-forming solution. The presence of this proteolipid determined some type of cationic selectivity which was not observed in the control. At a critical point of proteolipid concentration the conductance spontaneously fluctuated between two levels. The membrane current jumped from one state to another by way of single discrete steps, reminiscent of those obtained with the excitatory inducing material or the macrocyclic antibiotics. In membranes containing another proteolipid having no cholinergic binding properties, the increase in conductance was smaller, and had a linear function with the concentration. In this case the "flip flop" fluctuation and the cationic selectivity were not observed. The membranes containing the cholinergic proteolipid reacted to the addition of acetylcholine by a rapid and transient increase in conductance that was considerably reduced or abolished by a previous application of d-tubocurarine. These membranes also interacted with other cholinergic agents, such as gallamine triethiodide, hexamethonium, and alpha-bungarotoxin. These results suggest that this special proteolipid, when added to the artificial membranes, induces a "chemical excitability" toward cholinergic ligands.

Acetylcholine↗