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C Lippe

Publications and source records attributed to C Lippe.

At least 37 records · Page 2Linked to original sources
PubMed1987

Action of forskolin on non-electrolyte permeability across the frog skin as compared to that of vasopressin and isoprenaline.

Forskolin, a natural diterpene activating the adenyl cyclase in a receptor-independent manner, increases symmetrically both transepithelial fluxes of urea and erithrytol through the frog skin. The effect is dose-dependent, being 5 X 10(-6) M the dose necessary to obtain the maximal action. Forskolin-induced permeabilization is inversely proportional to the molecular weight of water soluble molecules (urea greater than erythritol greater than mannitol); also the permeability of a mainly lipid soluble molecule, i.e. antipyrine, is slightly increased by the diterpene. The permeability pattern is more similar to that induced by isoprenaline as compared to that elicited by vasopressin. Differently from what occurs in other tissues, small doses of forskolin (10(-8) M) are unable to potentiate the actions of vasopressin and isoprenaline on urea permeability across the frog skin. Moreover, the maximal action of forskolin is not additive with the maximal ones of isoprenaline and vasopressin.

Animals↗
PubMed1987

Effect of reagents of protein functional groups on the ADH-induced urea facilitated transport across toad urinary bladder.

1--The mechanism of the vasopressin-induced, facilitated transport across toad urinary bladder was studied by treating the luminal membrane of the epithelium with the following reagents of protein functional groups: NEM (SH groups), SITS (amino groups), EEDQ (carboxylic groups), DEPC (histidine). 2--Treatment of the luminal side of the epithelium by NEM strongly inhibits the ADH-induced urea transport, leaving unmodified the effect of the hormone on the flux of antipyrine, a lipid soluble molecule. These results confirm the hypothesis that the urea carrier is of proteic nature. 3--Treatment of the luminal side by SITS strongly inhibits ADH action on urea and antipyrine permeability; thus this effect can be considered rather unspecific. 4--On the contrary the EEDQ effect is more specific; in fact treatment of the luminal side by EEDQ strongly inhibits ADH effect on the permeability of urea, slightly increasing the ADH effect on that of antipyrine. 5--Finally, the luminal treatment by diethylpyrocarbonate inhibits almost completely the ADH action on the urea fluxes, slightly increasing the hormone effect on the antipyrine ones. 6--Based on these results we conclude that carboxylic groups and the imidazolic ring are more important than the amino groups in determining the urea transport across toad bladder, in the presence of ADH.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1985

Effect of vasopressin on the permeability of non electrolytes across the skins of Rana esculenta and Bufo bufo.

Maximal doses of vasopressin increase the permeability of the skins of Bufo bufo and Rana esculenta to urea, ethylene glycol, glycerol, erythritol, beta-alanine, leaving virtually unmodified that of mannitol and antipyrine. These results demonstrate that the response to vasopressin is quite different in amphibian skins as compared to the bladders. A careful analysis of the effects of vasopressin on non-electrolyte permeability as a function of their molecular weight demonstrates that hormone elicits the formation of pores with a diameter inferior to 4 A. Under vasopressin treatment the skins exhibit a selectivity for polyhydroxylated molecules as compared to urea and beta-alanine. This selectivity is not due to active of facilitated transport and is not impaired by phloretin or DTNB which selectively blocks the permeability of urea or ethylene glycol in erythrocytes. It is proposed that the site of such selectivity is located in other plasma membranes of the epithelium.

Animals↗
PubMed1983

[Effect of N-ethylmaleimide, introduced in to the serous fluid, on the active transport of sodium through the skin of Rana esculenta].

An SH reactive agent, N-ethylmaleimide (NEM), if introduced in the serosal bath (10(-4) M), stimulates the short circuit current (SCC) across the frog skin. This effect is due to an increase of Na active transport, because is inhibited by ouabain (10(-4) M). A stimulatory action on Cl- or HCO3- secretion can be ruled out because the rise in SCC occurs also in the absence of Cl- or HCO3-. It is known that NEM inhibits the ADH action by forming covalent bounds with SH groups of ADH membrane receptors (1). Thus it is possible that this binding should mimic the ADH action on SCC. In order to test this hypothesis, we studied the effect of serosal NEM on SCC both in the absence and in the presence of I midazol (20 mM), an activator of the cyclic AMP phosphodiesterase. Imidazol treatment decreases the effect of NEM on SCC. Thus we conclude that NEM serosal treatment is able to mimic some ADH effects, by using the same ways of the ormone action.

Animals↗
PubMed1982

[Effect of N-ethylmaleimide on the active transport of sodium and its permeability in the skin of Rana esculenta].

N-ethyl maleimide (10(-3)M in the external fluid) strongly increases the permeability of urea and phenylalanine. However, the ratio phi 0 urea / phi 0 phenylalanine (a measure of membrane integrity) is not reduced. NEM 10(-4)M elicits a small increase of urea permeability. NEM (10(-3)M or 10(-4)M in the external fluid) stimulates Na active transport across the frog skin. Most probably the activation of Na pump is due to an increase of Na cellular pool, caused by the permeability increase elicited by NEM.

Animals↗
PubMed1982

[The nature of urea transport across the skin of of Rana esculenta].

In several epithelial tissues such as toad bladder, gallbladder and human red cells, it has been established that urea movement implies a phloretin sensitive mediated transport. In the skin of the toad Bufo viridis also it has been described an active transport of urea. Our data, obtained on the frog skin seem to demonstrate the existence of some specific mechanism for urea transport towards the inside solution. In fact, two molecules having the some molecular diameter, such as urea and thiourea, show a large difference in permeability at low concentration. In addition 0.1 mM urea influxes and outfluxes, measured on paired skin halves in the absence of concentration gradient, exhibit an evident asymmetry. Further approaches with phloretin experiments were made in order to characterize the urea transport system. Phloretin (5.10(-4)M) added to the external solution significantly inhibits the urea influx. Little can be said at this time about the composition or kinetics of the carrier involved in the transport.

Animals↗
PubMed1982

Phloretin sensitive active urea absorption in frog skin.

This report presents evidence for urea active absorption by isolated skin of Rana esculenta. One of the supporting factors of such evidence is that at a low concentration the urea influx is five times greater than the outflux, in the absence of a chemical gradient. The transport shows a saturation kinetics with an apparent Km = 1.33 mM and is inhibited by un uncoupling agent (FCCP). 5 x 10(-4) M Phloretin, added to the external side, markedly inhibits inward urea transport, whereas it is ineffective when added to the serosal fluid. This provides evidence for a phloretin-sensitive mechanism located at the external side of the epithelium. Phloretin stimulates the sodium active transport; the possible coupling of urea and sodium movement is analysed.

Animals↗
PubMed1982

The nature of urea transport across the luminal membrane of Bufo bufo urinary bladder.

By using the washing-out technique, counterflow acceleration for urea was demonstrated on the luminal membrane of Bufo bufo urinary bladder, in the absence of ADH. This phenomenon completely disappears in the presence of phloretin 10-4 M on the luminal side and is consistent with the presence of a mobile carrier mechanism for urea transport across the luminal membrane, in basal conditions. In the presence of ADH, counterflow acceleration is completely absent. This result is in agreement with the presence of urea selective channels, induced by ADH, as proposed by Levine & Worthington (1976).

Animals↗
PubMed1980

[Evidence of morphological modifications induced by theophylline in the urinary bladder epithelium of Rana esculenta].

This preliminary work concerns the morpho-functional action induced by Theophylline on bladder epithelium. The epithelium treated with Theophylline shows important structural variations. The whole tissue thickness appears reduced with cell disposed in monostratified layer. They show a light grade of swelling with nucleus and cytoplasm less evident and boundary less marked. It is important to note that the permeability of the epithelium does not appear modified.

Animals↗
PubMed1980

Nonelectrolyte fluxes across gastric mucosa in relation to gastric stimulation. Is gastric juice secreted by osmosis or exocytosis?

The effects of histamine and thiocyanate, added to the serosal bathing solution, on unidirectional fluxes of some nonelectrolytes (thiourea, methylated thiourea derivates, mannitol), and on H+, pepsinogen and mucous secretion were investigated in frog (Rana esculenta) fundic gastric mucosa. Histamine (10(-4) M) increases significantly the outfluxes (serosa to mucosa fluxes) of only thiourea and its derivates (but not mannitol) and the stimulation is the greater the more lipidsoluble the nonelectrolyte is. Influxes (mucosa to serosa fluxes) of the same molecules are not affected. In parallel histamine stimulates H+-secretion but does not modify pepsinogen and mucous secretion. SCN- (10(-2) M) inhibits the histamine effect on thiourea outfluxes and on H+-secretion, while pepsinogen and mucous secretion are not affected. Colchicine (10(-4) M) pretreatment inhibits the histamine effect on outfluxes and H+-secretion. It is concluded that: (1) histamine induces a secretion of nonelectrolytes towards the lumen; (2) such secretion is correlated with the hormone-induced secretion of HCl and fluid; (3) this process is mediated by an exocytotic mechanism.

Animals↗
PubMed1980

Polar distribution of sodium-dependent and sodium-independent transport system for L-lactate in the plasma membrane of rat enterocytes.

The uptake of L-lactate by rat small intestinal brush-border and basal-lateral plasma membrane vesicles has been studied. L-Lactate uptake by the isolated membrane vesicles is osmotically sensitive and represents predominantly transport into an intravesicular space and not binding to the membranes. The transport of L-lactate across the brush-border membrane is stimulated by sodium, whereas the transport across the basal-lateral plasma membrane is sodium-independent. In both types of membrane vesicles L-lactate is transported faster than D-lactate and L-lactate transport is inhibited by alpha-cyano-cinnamic acid. L-Lactate transport across basal-lateral membranes is inhibited by D-lactate and pyruvate and transstimulated by L-lactate and pyruvate. The polar distribution of transport system for L-lactate in the plasma membrane of rat enterocytes--a Na+/L-lactate cotransport system in the brush-border membrane and a facilitated diffusion system in the basal-lateral membrane--can explain the fact that in the intact epithelium L-lactate produced by cell metabolism is preferentially released on the serosal side and could enable the cell to perform vectorial, secondary active transport of L-lactate from the intestinal lumen to the serosal compartment.

Animals↗
PubMed1980

Effect of cycloheximide on urea facilitated transport through toad gallbladder epithelium.

Transepithelial urea outfluxes across toad gallbladder were determined before and after the addition of cycloheximide. The drug inhibits the movement of urea but has no effect on thiourea and antipyrine outfluxes. The inhibition of amide transport is time dependent as also shown in counterflow experiments. These results are consistent with the hypothesis that cycloheximide inhibits the synthesis of membrane proteic sites involved in urea mediated transport.

Animals↗