PubMed Health⌕ Search

Biomedical subjects

M Parisi

Publications and source records attributed to M Parisi.

At least 73 records · Page 4Linked to original sources
PubMed1988

Calcitonin is a competitive inhibitor of the hydrosmotic effect of oxytocin in toad bladder.

The effects of calcitonin (CT) on the water transfer in the toad (Bufo arenarum) urinary bladder, an epithelial barrier commonly employed as a model of the mammalian nephron, were studied. The net transmembrane water flux was measured at minute intervals, while the endogenous adenosine 3',5'-cyclic monophosphate (cAMP) levels were determined in isolated epithelial cells. It was observed that 1) CT, up to 10(-6) M, did not have any effect on water permeability. 2) Preincubation with CT, between 10(-7) and 10(-8) M, inhibited the hydrosmotic response to a supramaximal dose of oxytocin (OXT; 2 x 10(-8) M), used here as an antidiuretic hormone (ADH) analogue. This inhibition was reversible and concentration related. Nevertheless, although the magnitude of the response was reduced, its time course of evolution did not change. 3) When CT was added on the previously developed response to OXT, inhibition was also dose dependent with a time course not distinguishable from hormonal washout. 4) CT, up to 10(-6) M, did not modify the hydrosmotic response to 8-bromo cAMP, a potent analogue of the ADH second messenger. 5) CT and OXT increased the intracellular cAMP levels, but both effects were not cumulative. The increase induced by CT plus OXT was significantly lower than the one elicited by OXT alone. It is concluded that CT is a competitive inhibitor to the hydrosmotic effect of OXT in toad urinary bladder. Its action must be located prior to cAMP formation.

Animals↗
PubMed1987

Intracellular Ca2+ concentration and the antidiuretic hormone-induced increase in water permeability: effects of ionophore A23187 and quinidine.

The hydroosmotic responses induced by oxytocin and 8-bromo-cyclic AMP, in frog and toad urinary bladders, were recorded minute by minute. 3HHO and 45Ca unidirectional fluxes as well as prostaglandin B2 liberation were also measured. It was observed that: (1) Addition of the calcium ionophore A23187 or quinidine to the serosal bath inhibited the response to oxytocin, but not to 8-bromo-cyclic AMP, while increasing prostaglandin E1 liberation into the serosal but not into the mucosal bath. (2) Addition of A23187 to the mucosal bath induced a transient and temperature-dependent inhibition of the response elicited by 8-bromo-cyclic AMP. The time-course of this reduction in water permeability and its sensitivity to medium temperature were similar to those observed after the withdrawal of agonist, but clearly different of those observed after intracellular acidification. (3) The hydroosmotic response was also transitorily inhibited when the Ca2+ concentration was step-changed in the mucosal bath. (4) When added to the mucosal or to the serosal baths, the ionophore increased either the apical or the laterobasal Ca2+ permeabilities. It is concluded that manipulation of intracellular Ca2+ interferes with the hydroosmotic response at two different levels. (1) A first target point located 'pre-cyclic-AMP production'. This effect would be mediated by prostaglandin liberation. (2) A second target point located after cyclic AMP production and before the 'temperature-dependent rate-limiting step'. This effect is probably related to the mechanism controlling the insertion and removal of water channels.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1987

Single channel recordings from basolateral membranes of frog urinary bladders.

A methodology is described to obtain, in frog urinary bladder, isolated epithelial layers suitable for patch clamp studies. This was achieved combining negative pressure, enzymatic digestion, and microdissection. Single channels recordings were obtained from the basolateral membranes while the tissue maintained its general structure and polarity.

Animals↗
PubMed1985

The role of microtubules and microfilaments in the hydrosmotic response to antidiuretic hormone.

To test the effects of colchicine and cytochalasin B on the ADH-induced response, unidirectional and net water fluxes were measured at one or two minutes intervals in frog urinary bladder. The action of these agents on the appearance of intramembrane particles aggregates in the luminal membrane of target cells under oxytocin stimulation and the changes in the tissue ultrastructure induced by cytochalasin B were also studied. It was observed that: the time-course of the response to oxytocin was strongly slowed by colchicine while the washout was not affected; the time-course of the 'on and off' of the response to oxytocin was not modified by cytochalasin B; cytochalasin B pretreatment proportionally reduced unidirectional and net water fluxes measured after glutaraldehyde fixation; the combined action of colchicine and cytochalasin B proportionally reduced the net water flux and the number of intramembrane particles aggregates, observed in freeze-fracture studies; after cytochalasin B action the dilation of intercellular spaces classically observed under oxytocin stimulation is strongly reduced. It is concluded that: microtubules probably play an important role in the water channels plug-in, but not in their removal; microfilaments integrity is necessary for the mechanisms inducing intercellular space dilation and the observed results confirm that water permeability is controlled by the number of permeation units present in the luminal border of granular cells and probably represented by the intramembrane particle aggregates.

Animals↗
PubMed1985

Glutaraldehyde fixation preserves the permeability properties of the ADH-induced water channels.

Unidirectional and net water movements were determined, in frog urinary bladders, before and after glutaraldehyde fixation. Experiments were performed in three experimental conditions: in nonstimulated preparations, after the action of antidiuretic hormone (ADH) and in nonstimulated preparations to which amphotericin B was incorporated from the luminal bath. As previously observed for net water fluxes, the increase in the unidirectional water movement induced by ADH was well preserved by glutaraldehyde fixation. After correction for the effects of unstirred layers and nonosmotic pathways, the observed correlation between the ADH-induced increases in the osmotic (Pf) and diffusional (Pd) permeability coefficients was not modified by the fixative action (before glutaraldehyde: slope 11.19, r: 0.87 +/- 0.07; n = 12; after glutaraldehyde: slope 10.67, r: 0.86 +/- 0.04, n = 39). In the case of amphotericin B, delta Pf/delta Pd = 3.08 (r: 0.83 +/- 0.08), a value similar to that observed in lipid bilayers or in nonfixed toad urinary bladders. It is concluded that: The experimental approach previously employed to study water channels in artificial lipid membranes and in amphibian urinary bladders, can be applied to the glutaraldehyde-fixed frog urinary bladder. Glutaraldehyde fixation does not modify the permeability properties of the ADH-induced water channels. Any contribution of exo-endocytic processes or cell regulatory mechanisms to the observed permeability parameters can probably be excluded. Glutaraldehyde-fixed preparations are a good model to characterize these water pathways.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1984

Cellular pH and the ADH-induced hydrosmotic response in different ADH target epithelia.

The hydrosmotic response elicited by oxytocin in the frog skin epithelium (Rana esculenta) was reversibly inhibited by 70% when the medium pH was reduced to 6.2 by CO2 bubbling on the serosal side. On the contrary, the response to 8-bromo cyclic AMP (8 Br-CAMP) was not affected by medium acidification, even after corion removal. In other experiments intracellular pH was measured, employing the dimetyl-oxazolidine-dione distribution technique, in frog urinary bladder and the isolated frog skin epithelium. As previously observed in the case of oxytocin, 8 Br-CAMP increased intracellular pH in frog urinary bladder. Incubation with oxytocin also augmented the intracellular pH in the isolated frog skin epithelium but 8 Br-CAMP did not modify cell proton concentration in this tissue. From previous and present results it can be summarized that: 1) The intracellular alkalinization effect elicited by oxytocin addition and the inhibition in the hydrosmotic response induced by medium acidification were qualitatively similar in both tested target epithelia. 2) On the contrary, a post cyclic AMP step sensitive to changes in intracellular pH was not observed in frog skin, as is the case in frog urinary bladder. 3) The 8 Br-CAMP induced intracellular alkalinization effect was only observed in frog urinary bladder.

Animals↗
PubMed1984

Effects of cellular acidification on ADH-induced intramembrane particle aggregates.

8-Bromoadenosine 3',5'-cyclic monophosphate [an analogue of adenosine 3',5'-cyclic monophosphate (cAMP), the intracellular mediator for antidiuretic hormone (ADH) action] induces, in frog urinary bladder, an increase in water permeability that is rapidly and reversibly inhibited by cellular acidification. The effect of CO2 bubbling on the simultaneously observed intramembranous particle aggregates, which probably represent water channels, depended on the time that elapsed after changing medium pH: 3 min of CO2 bubbling depressed the water flux by 70%, whereas the membrane surface occupied by the aggregates remained unchanged. On the contrary, after 9-15 min of CO2 bubbling, both the water flux and the surface area occupied by the aggregates were strongly reduced. These results can be interpreted by accepting two post-cAMP levels of action for cellular acidification: 1) the channels themselves that, as previously suggested by ADH experiments at low temperature, would shift their structure from an "open" to a "closed" state, and 2) the mechanism that controlled the aggregates' plug in and removal.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1984

The onset and offset of the hydrosmotic response in frog epithelia.

The onset and offset of the hydrosmotic responses elicited by different agonists in frog urinary bladder, frog skin and isolated frog skin epithelium were studied and compared. The removal of the frog skin supporting layers accelerated the onset of the reactions to oxytocin and 8-bromo-cyclic AMP (8-Br-cAMP), which, however, remained slower than the onset in the urinary bladder. The offset of these actions was not affected by corion removal and was also slower than in the bladder. A marked asymmetry between onset and offset of the hydrosmotic response was observed when the isolated skin epithelium was stimulated with 8-Br-cAMP. The results show that the increases in water permeability elicited by oxytocin and cyclic-AMP derivatives in frog skin and frog urinary bladder, although attributable to the same general mechanisms, present different specific characteristics.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1983

The rate-limiting step in hydrosmotic response of frog urinary bladder.

The ADH-induced water fluxes and the associated appearance of intramembranous particle aggregates in the luminal membrane of frog urinary bladders have been correlated in a time course study. Plots of the onset and reversal of the oxytocin-induced hydrosmotic response were sigmoidal in shape, symmetrical and slowed by low temperature to the same degree. Parallel freeze-fracture studies showed that the mean size distribution of the aggregates was constant at different temperatures and at different times during hormonal stimulation and washout. No qualitatively different picture of aggregate formation was detected at low temperature: this suggests that the insertion and removal of individual aggregates into or from the apical plasma membrane is a rather rapid process, both at 20 and at 6.5 degrees C. As in the case of water permeability, both aggregate appearance and disappearance were similarly slowed by lowering the temperature. A similar time-course study of the inhibition of the hydrosmotic response by acidification of the medium was also made. In this case, lowering the incubation temperature induced a clear dissociation between net water flow and the surface area occupied by the aggregates. For the first time, a low water permeability was found associated with a high aggregate surface area in the apical membrane, indicating that cellular acidification induces an impairment of aggregate function rather than a reduction of surface area.

Animals↗
PubMed1983

The single file hypothesis and the water channels induced by antidiuretic hormone.

Unidirectional and net water movements were determined at minute intervals in frog urinary bladders. The changes in both parameters were followed, during the action of antidiuretic hormone (ADH), at different temperatures and stirring conditions. After correction for external unstirred layer effects, the ratio of the osmotic (Pf) and diffusional (Pd) permeability coefficients was remarkably constant, at different times and in different experimental conditions. In the presence of ADH the delta Pf/delta Pd ratio in the mucosal border was probably greater than 9. On the other hand, in nonstimulated preparations the ratio was smaller, and probably not different from 1. These results, together with previous observations indicating that other small molecules (like urea) are excluded from the ADH-induced channel, might indicate that single-file water movement can occur through this structure. Alternatively, the delta Pf/delta Pd ratio could result from a complex geometric arrangement in series with the aqueous pore.

Animals↗
PubMed1983

Intracellular pH, transepithelial pH gradients, and ADH-induced water channels.

Urinary bladders of frogs were exposed to a transepithelial proton and osmotic gradient (serosal pH 8.1, Tris or bicarbonate buffer; mucosal pH 5.8, unbuffered) while the alkalinization rate of the mucosal bath and the net water movement were simultaneously monitored. It was observed that 1) the mucosal alkalinization rate was dependent on serosal pH and buffer; 2) oxytocin increased the mucosal alkalinization rate only when serosal bicarbonate was employed, whereas the net water movement augmented both when serosal bicarbonate or Tris buffers were used; 3) amiloride did not modify the mucosal alkalinization rate either before or after oxytocin; 4) the increases in the mucosal alkalinization rate and in the net water movement induced by oxytocin (serosal bicarbonate) were negatively correlated. In other experiments intracellular pH (pHi) was estimated with the DMO distribution technique with the following results. 1) Oxytocin increased the pHi when either serosal bicarbonate or Tris buffers was used and even in the presence of a low mucosal pH (Tris buffer, pH 5.8). 2) Important cellular acidification was observed when CO2 was bubbled (to pH 5.8), whereas the hydrosmotic response to 8-bromo-cAMP was clearly inhibited. These results indicate that cellular alkalinization could play a pivotal role in action of ADH, show that ADH can modify the transepithelial pH equilibrium mechanism, and suggest that intracellular pH regulation and water permeability control can be linked regulatory processes.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1982

Detergent extraction of membrane proteins related to the action of antidiuretic hormone.

Antidiuretic hormone (ADH) induces, in the apical plasma membrane of target cells, the insertion of intramembranous particle aggregates that probably contain water channels. A mild attack of this membrane by a polyoxyethylene nonylphenyl detergent, which reversibly depressed ADH-induced water permeability, has been found to modify aggregate structure while extracting additional proteins. This simple procedure could be a valuable approach to the problem of aggregate isolation and characterization.

Animals↗
PubMed1981

Cellular pH and water permeability control in frog urinary bladder. A possible action on the water pathway.

Mucosal acidification (from pH 8.1 to 6.0) reversibly inhibited the hydroosmotic responses to oxytocin, cyclic AMP and 8-bromo-cyclic AMP in frog urinary bladder. These inhibitory effects were only observed in the presence of a permeant buffer in the apical medium and could also be elicited by CO2 bubbling, even when the mucosal pH was clamped at 8.1. Acid pH reduced the oxytocin-induced net water flux faster than norepinephrine or oxytocin removal and the difference was especially important at low temperature. The time course of recovery from acid pH inhibition was, at 20 degree C, similar to that of the hormonal action, but when the medium temperature was reduced to 6-7 degrees C, the recovery from acid pH inhibition paradoxically became faster while the oxytocin action was markedly slowed down (t 1/2 of changes in net water fluxes (expressed in min): oxytocin addition at 20 degrees C, 6.2 +/- 0.9; at 6 degrees C, 24 +/- 3; oxytocin removal at 20 degrees C, 4.7 +/- 0.8; at 6 degrees C, 22 +/- 3; pH inhibition at 20 degrees C, 2.6 +/- 0.2, at 6 degrees C 2.5 +/- 0.2; recovery from pH 6 at 20 degrees C 6.5 +/- 0.9; at 6 degrees C, 2.7 +/- 0.3). These results can be explained by accepting two main loci sensitive to medium acidification: (1) the cyclase system and (2) an intracellular, temperature-independent, post-cyclic AMP site. The fact that the intramembranous particle aggregates associated with the oxytocin-induced water permeability increase did not disappear after the flow inhibition by acid pH at low temperature suggests that the second effect could be located at the water channel itself.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1981

[Role of ADH-induced intramembrane particle aggregates (author's transl)].

In certain epithelial tissues, water permeability is markedly increased by antidiuretic hormone. This so-called hydrosmotic effect has been shown to be mediated by 3'-5' cyclic adenosine monophosphate, which, in turn, alters the permeability o the luminal membrane of receptor cells. This review deals wity ultrastructural alterations occurring in the membrane, as observed with freeze-fracture electron microscopy. Basically, these alterations consist of organized particle aggregates which appear in the apical membrane. In all experimental conditions, similar aggregates can be observed in the membrane of cytoplasmic vesicles. ADH stimulation triggers the fusion of these vesicles with the apical membrane resulting in the concomitant transfer of particle aggregates. It has been shown, in a wide range of experimental conditions, that both number and total area of the aggregates are directly proportional to the water permeability of the tissue. It is generally assumed that particle aggregates contain transmembrane channels that are selectively to water.

Amphibians↗
PubMed1980

Water permeability of the toad corneal epithelium: the effects of pH and amphotericin B.

The water diffusional permeability of the toad cornea was evaluated from THO measurements, while taking into account the influence of unstirred layers. The corneal epithelium is a restrictive barrier for water diffusion and its permeability can be increased by amphotericin B or Triton X-100. In animals maintained in tap water, the epithelial water permeability was reversibly inhibited by the acidification of the solution bathing the tear side of the cornea. When toads were adapted to a saline environment, a reduction of epithelial water permeability with a loss of sensitivity to changes in the tear side medium pH was observed.

Amphotericin B↗