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J Aboulafia

Publications and source records attributed to J Aboulafia.

14 recordsLinked to original sources
PubMed1999

Desensitization to ANG II in guinea pig ileum depends on membrane repolarization: role of maxi-K(+) channel.

Desensitization of ANG II tonic contractile response of the guinea pig ileum is related to membrane repolarization determined by Ca(2+)-activated K(+) (maxi-K(+)) channel opening. ANG II-stimulated depolarized myocytes presented sustained activation of maxi-K(+) channels, characterized by reduction from 415 to 12 ms of the closed time constant. ANG II desensitization was prevented by 100 nM iberiotoxin, being reversible within 30 min. Depolarization by KCl, higher than 4 mM, impaired desensitization, suggesting that the membrane potential must attain a threshold to counteract the repolarization induced by maxi-K(+) channel opening. Once this value is attained, there is no time dependency because the desensitization process was shut off by addition of KCl along the time course of the tonic response. In contrast, the sustained ACh tonic component was not altered by these maneuvers. We conclude that desensitization of the ANG II tonic component is foremost due to the opening of maxi-K(+) channels, leading to membrane repolarization, thus closing the voltage-dependent Ca(2+) channels responsible for the Ca(2+) influx that sustains the tonic component in this muscle.

Acetylcholine↗
PubMed1998

Activation of Ca(2+)-activated K+ (maxi-K+) channel by angiotensin II in myocytes of the guinea pig ileum.

We investigated the regulation of the Ca(2+)-activated K+ (maxi-K+) channel by angiotensin II (ANG II) and its synthetic analog, [Lys2]ANG II, in freshly dispersed intestinal myocytes. We identified a maxi-K+ channel population in the inside-out patch configuration on the basis of its conductance (257 +/- 4 pS in symmetrical 150 mM KCl solution), voltage and Ca2+ dependence of channel opening, low Na(+)-to-K+ and Cl(-)-to-K+ permeability ratios, and blockade by external Cs+ and tetraethylammonium chloride. ANG II and [Lys2]ANG II caused an indirect, reversible, Ca(2+)- and dose-dependent activation of maxi-K+ channels in cell-attached experiments when cells were bathed in high-K+ solution. This effect was reversibly blocked by DUP-753, being that it is mediated by the AT1 receptor. Evidences that activation of the maxi-K+ channel by ANG II requires a rise in intracellular Ca2+ concentration ([Ca2+]i) as an intermediate step were the shift of the open probability of the channel-membrane potential relationship to less positive membrane potentials and the sustained increase in [Ca2+]i in fura 2-loaded myocytes. The preservation of the pharmacomechanical coupling of ANG II in these cells provides a good model for the study of transmembrane signaling responses to ANG II and analogs in this tissue.

Angiotensin II↗
PubMed1995

Angiotensin II tachyphylaxis in the guinea pig ileum and its prevention: a pharmacological and biochemical study.

Angiotensin II (AII) tachyphylaxis occurs in the guinea pig ileum, but is not induced by analogs lacking the N-terminal amino group or the Arg2 guanidino group. Both AII and Lys2AII increased cell inositol trisphoshate content in cultured intestinal smooth muscle cells. Protein kinase C inhibition by staurosporine or downregulation by prolonged incubation with phorbol reverted tachyphylaxis of the inositol trisphoshate response, but not that of the Na+ uptake response, indicating that the uncoupling of the phosphoinositide signal system by protein kinase C did not involve all processes distal to receptor activation. Tachyphylaxis of the Na+ uptake response was prevented when receptor internalization was blocked by reduction of the temperature (4 degrees C) or by pretreatment of the cells with phenylarsine oxide. Acid washings, which prevented tachyphylaxis of the 24Na+ influx response, also prevented tachyphylaxis of the contractile response of the guinea pig ileum to AII. Although these findings suggest that sequestration or internalization of the AII receptor might be involved in AII tachyphylaxis, binding of [125I]AII and of [125I]Lys2AII to the cells was equally unaffected by repeated administrations of the peptides. The results suggest that conformational change of the AII-receptor complex within the plasma membrane, but not internalization, is the most important factor responsible for tachyphylaxis.

Alkaloids↗
PubMed1994

A Na(+)-sensitive cation channel modulated by angiotensin II in cultured intestinal myocytes.

Single-channel currents were recorded in excised inside-out and cell-attached patches of cultured cells from the longitudinal smooth muscle of the guinea pig ileum. In the presence of symmetrical high-K+ solutions, we identified a voltage-dependent 12-pS channel. It was reversibly blocked by addition of either Ba2+ or Cs+ at the cellular side of the patch but was insensitive to Ca2+ or ATP. This channel had poor selectivity concerning cations (PLi > PK = PNa = PCa, where P is permeability) and low permeability to anions. Isosmotic substitution of NaCl for KCl in the solution facing the cellular side enhanced the channel activity by increasing NPo values where N is number of channels and Po is open probability. In the cell-attached configuration, the channel was also activated by addition of angiotensin II in the bath solution. We propose that this nonselective cation channel might play a role in the control of the membrane potential during the contractile response of the guinea pig ileum to agonists by keeping the voltage-sensitive Ca2+ channels open.

Angiotensin II↗
PubMed1989

Angiotensin II desensitization and Ca2+ and Na+ fluxes in vascular smooth muscle cells.

The role of ion fluxes in angiotensin II (AII) desensitization (tachyphylaxis) was investigated by studying Na+ and Ca2+ translocation in cultured vascular smooth muscle cells from the rat aorta. The effects of AII were compared to those of [1-sarcosine]-AII (Sar1-AII), an analogue which also induces tachyphylaxis, and [2-lysine]-AII (Lys2-AII), an analogue that does not show this property. Maximally effective concentrations of the three peptides induced a rapid and transient increase in 45Ca2+ efflux, a rapid and sustained decrease in total cell Ca2+ and an increased Na+ permeability. Repeated treatments, at short intervals, with either of the three peptides abolished the effect on Ca2+ efflux, and this desensitization was slowly reversible. A 30-min rest period was sufficient for full recovery of the response of cells that were desensitized by Lys2-AII, whereas the recovery from AII or Sar1-AII-desensitization was still not complete after 60 min. Our results suggest that the difference in the behaviour of the "tachyphylactic" AII and Sar1-AII and the "non-tachyphylactic" Lys2-AII lays not in the production of different signals upon binding to the receptor, but in a difference in the hormone-receptor interaction itself.

Angiotensin II↗
PubMed1987

Sodium-dependence of the non-specific desensitization of the guinea-pig ileum induced by acetylcholine and histamine.

The isometric maximal responses of the guinea-pig ileum to acetylcholine and to histamine (but not those to prostaglandin E2 and to high K+) exhibited a secondary transient increase in tonus during the tonic component of the contraction. After desensitizing treatment with acetylcholine or histamine, the isometric responses to either agonist showed decreased phasic and enhanced tonic components, whereas both components of the response to prostaglandin E2 were markedly depressed. During the desensitizing treatment the degree of desensitization went through a maximum that coincided with the occurrence of the secondary tonic increment. In low-Na+ medium, or in ouabain-treated tissues, the responses to the three agonists were similar to the respective responses in the desensitized state. It is concluded that the non-specific desensitization is due to changes in Na+ translocation and that the increased tonic component of the isometric response is due to a reduced Na+ gradient across the cell membrane and consequent increase in Ca2+ loading.

Acetylcholine↗
PubMed1985

Lack of PCMB action upon the outer barrier sodium permeability in the absence of Na in toad skin.

The stimulation of apical Na permeability by p-chloromercuribenzoate (PCMB) was evaluated by studying its effect on unidirectional 24Na flux (JNaeff) from inner to outer compartment in the isolated short-circuited toad skin. With Na present in the inner compartment, addition of PCMB to the outer skin surface led to an increase of JNaeff. However, after replacing all Na of the inner compartment by K or choline, the amiloride inhibitable Na permeability of the outer cell membrane increased, and PCMB was no longer effective. It is concluded that PCMB releases the blocking effect of intracellular Na on apical Na channels. If intracellular Na is drastically reduced virtually all Na channels are opened so that PCMB does no longer act.

Amiloride↗
PubMed1985

Hydrosmotic salt effect in toad skin: urea permeability and glutaraldehyde fixation of water channels.

The "hydrosmotic salt effect" (HSE), the reversible dependence of skin osmotic water permeability upon the ionic concentration of the outer bathing solution, is known to induce the appearance of sucrose-impermeable pathways in the apical membrane of the outermost epithelial cell layer. Diffusional 14C-urea permeability, measured in the Jv = O condition to prevent solvent drag effects, indicates that the newly formed pathways induced by HSE are narrower than the size of the urea molecule, being therefore highly selective for water molecules. After mild glutaraldehyde (2% solution) fixation of the apical membrane structures, the water channels induced by the HSE are no longer affected by the ionic strength of the outer solution. This indicates that the channel-forming membrane protein can be fixed in different configurations with the water channels in the open or closed states.

Animals↗
PubMed1984

Vanadate and ouabain: a comparative study in toad skin.

In this study we compare the effects of two inhibitors of the Na,K-ATPase, ouabain and vanadate, upon transport properties of the isolated short-circuited toad skin: The main conclusions are: Both inhibitors induce a similar decline in short-circuit current (SCC). They differ regarding skin electrical resistance (R). Ouabain induces an increase in resistance that, after some delay, builds up slowly after its addition to the preparation, while vanadate causes a fast increase in resistance that remains constant for most of the experimental period. Vanadate, but not ouabain, promotes an unspecific increase in skin permeability characterized by a delayed and progressive rise of 42K (JK eff) and 14C sucrose (J suc eff) effluxes. Vanadate effect upon skin permeability, as measured by JK eff, is not affected by pre-treating the skin with DIDS, a stilbene derivative, indicating that anion-exchange is not an important step for the entrance of vanadate into the epithelial cells to trigger its effect. Vanadate effect upon JK eff is also not affected by previous ouabain inhibition of the Na,K-ATPase, showing that this effect is not mediated by the inhibition of this enzyme. Vanadate action in toad skin seems to occur at junctional structures opening paracellular routes. A possible mechanism for the effect of vanadate is discussed in terms of cytosolic Ca2+ balance, cytoskeleton and their interplay with the sealing of tight junctions.

Animals↗
PubMed1983

Cellular Li+ opens paracellular path in toad skin: amiloride blockable effect.

The presence of Li in the solution bathing the outer surface of toad skin under short-circuit condition promotes an unspecific permeability increase characterized by a delayed and progressive increase in the effluxes of 24Na, 42K and 14C sucrose. The effect of Li upon sucrose permeability might indicate an increased permeability of the paracellular pathway. The Li effect is mediated by an intracellular action since blockade of Li entrance into the cell compartment by amiloride prevents the increase in Na, K and sucrose permeability. A possible mechanism of this effect is discussed in terms of a disturbance in the cellular Ca++ balance leading to an increase in cytosolic Ca++ concentration which perturbs the organization of the cytoskeleton and the interplay between cytoskeleton and tight junctions.

Amiloride↗
PubMed1976

Evidence against cholinergic mediation of the effect of angiotensin II on the guinea pig ileum.

The belief that the smooth muscle contracting activity of angiotensin II (angiotensin) in the guinea pig ileum is partly mediated by release of acetylcholine was reexamined, with the following results. 1. Atropine did not reduce the maximum contraction produced by angiotensin, although it caused a shift to the right of the log dose-response curve (dose ratio = 2.2). A similar shift was observed with histamine, bradykinin and BaCl2. 2. A moderate potentiation of angiotensin by eserine was also observed, which was similarly found for the other agonists. 3. A previous report that atropine blocks the fast (phasic) component of the isometric response of the ileum to angiotensin was not confirmed. The disappearance of the phasic component was found to be due to a tachyphylactic change in the response. 4. Depolarization by high doses of nicotine, and inhibition of acetylcholine synthesis by hemicholinium, did not affect the response to angiotensin. 5. Ilei in which the intramural ganglia had been destroyed by incubation at 4 degrees 48-56 h responed maximally to angiotensin, without loss of the phasic component of the response. It is concluded that the available evidence does not support the participation of a cholinergic mechanism in the effect of angiotensin upon the guinea pig ileum.

Angiotensin II↗
PubMed1976

Tachyphylaxis and angiotensin receptors.

Angiotensin tachyphylaxis was studied in the isolated guinea pig ileum under isometric conditions. 2. In tachyphylactic organs, the initial phasic response to angiotensin was abolished, while the tonic component of the response became faster in its onset and in its reversal (relaxation). 3. The relaxation of non-tachyphylactic organs after angiotensin washout was significantly slower than with bradykinin, des-amino-angiotensin and hexanoyl-angiotensin. This difference did not occur in tachyphylactic organs. 4. There was no correlation between production of tachyphylaxis or rate of relaxation after washout and the partition coefficient of the four peptides in an organic:aqueous solvent system. 5. It is suggested that tachyphylaxis depends on a slowly reversible alteration of a calcium translocation step in the stimulus-response coupling.

Angiotensin II↗
PubMed1976

Effect of indomethacin and prostaglandin on the smooth muscle contracting activity of angiotensin and other agonists.

Indomethacin had an equal inhibitory effect on the response of the guinea-pig isolated ileum to angiotensin II (angiotensin), bradykinin, histamine and acetylcholine. This effect did not seem to result from inhibition of prostaglandin synthesis, as it did not depend on the time of treatment with indomethacin. Prostaglandin E2 (prostaglandin) potentiated the responses of the guinea-pig ileum to angiotensin, bradykinin, histamine and acetylcholine without significant differences in the effects observed. In the rabbit isolated mesenteric and coeliac arteries, indomethacin had an equal potentiating effect on the responses to angiotensin and to adrenaline. In these organs pre-incubation with indomethacin was necessary for the effect to be observed, and this effect lasted for 2 h or more after that drug was removed from the medium. No cross-tachyphylaxis between angiotensin and adrenaline was observed in the rabbit mesenteric and coeliac arteries. It is concluded that the effects of indomethacin and prostaglandin on the response of the guinea-pig ileum to the four agonists result from an action on the smooth muscle contractile mechanism per se rather than from an inhibitory action on the release of endogenous prostaglandin produced by the four agonists. The results with the rabbit isolated arteries indicate that tachyphylaxis to angiotensin in these organs is not caused by prostaglandin release.

Acetylcholine↗