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N Eleno

Publications and source records attributed to N Eleno.

36 records · Page 2Linked to original sources
PubMed1994

Membrane potential dependence of the kinetics of cationic amino acid transport systems in human placenta.

1. Mediated influx of L-lysine into human placental brush-border membrane vesicles occurs through two systems, one of lower affinity but high capacity, the other of very high affinity but low capacity. These transporters have features characteristic of systems y+ (the classical system) and y+L (recently described in the erythrocyte), respectively. 2. In solutions containing sodium the entry of lysine through the high-affinity system (y+L) is inhibited by the neutral amino acids L-leucine, L-methionine and L-glutamine with comparable high affinity. The removal of sodium reduces the affinity but not the maximal extent of this inhibition. Leucine and methionine, but apparently not glutamine, inhibit lysine entry through system y+ with a much lower affinity. 3. The influx of lysine through system y+ changes markedly in response to alterations of membrane potential. In the presence of an inwardly directed negative diffusion potential created by an inwardly directed thiocyanate (SCN-) gradient, the influx of lysine through this route is accelerated; with an inwardly directed positive potassium diffusion potential, lysine influx through this route is reduced. The influx of lysine through system y+L is much less sensitive to such alterations of potential. 4. Analysis of the kinetic constants characterizing system y+ shows that with a change of potential from zero to negative (approximately -60 mV) the maximum velocity (Vmax) is roughly doubled and the half-saturation constant (Km) halved leading to a 4-fold increase in permeability. For system y+L smaller changes are seen and Km does not change; the resulting increase in y+L permeability is 1.5-fold. 5. These findings are discussed with respect both to the mechanism of membrane transport and placental epithelial function.

Amino Acids↗
PubMed1994

Effects of a new dihydropyridine derivative, S12968 (pranedipine), and its stereoisomer, S12967, on renal effects of endothelin-1.

The purpose of the present study was to assess in rats the prevention by two enantiomers of a new dihydropyridine derivative (pranedipine) (called S12967 for the dextrogyre (+) and S12968 for the levogyre (-) molecules) of the renal and cardiovascular effects induced by endothelin-1. The injection of endothelin-1 (1 nmol/kg body weight) induced a sharp and transient decrease in urine flow, sodium and potassium excretion, glomerular filtration rate, renal plasma flow, and renal blood flow, a significant increase in renal vascular resistance, and a small but significant increase in arterial pressure. Treatment with S12968 alone (0.3 mg/kg) induced a 2.5-fold increase in urine flow and potassium excretion and a 4.5-fold increase in sodium excretion. Pretreatment with S12968 completely blocked the endothelin-1 induced increase in arterial pressure, did not affect the acute effect of endothelin-1 on urine flow, sodium and potassium excretion, filtration rate, and renal blood flow, but blunted the effect on renal vascular resistance. Administration of S12967 alone (1 mg/kg) did not induce changes in either renal function or arterial pressure. In S12967-treated animals, endothelin-1 also induced a transient increase in arterial pressure nad renal vascular resistance but failed to change renal function in a significant manner. In summary, the above reported experiments show that at the higher, nonhypotensive doses, the levogyre enantiomer (S12968) of a new dihydropyridine derivative (pranedipine) completely prevented the hypertensive effect of endothelin 1, and partially prevented the effect of endothelin-1 on renal vascular resistance. The dextrogyre enantiomer (S12967) had almost no effect on either mean arterial pressure or renal vascular resistance but completely blocked the endothelin-1-induced decrease in urine flow and urinary sodium excretion.

Animals↗
PubMed1992

Substrate-specific differences in the rate of bile acid carrier reorientation: studies on human placental basal vesicles.

The initial rate of transport of the bile acid glycocholic acid (GCA) has been measured in influx and efflux across placental basal membrane vesicles, and the mechanism of inhibition of its transport by the analogue taurochenodeoxycholic acid (TCDCA) analysed kinetically. This analogue, although trans-stimulating GCA efflux, inhibits influx in a way which does not depend upon substrate concentration; moreover, its potency as an inhibitor is markedly influenced by whether it is placed on one or on both sides of the vesicles membrane. These findings can be accounted for by postulating that both GCA and TCDCA are translocated through the carrier, but that the rate of loaded carrier reorientation is higher than that of the free carrier only when loaded with TCDCA and not with GCA.

Bile Acids and Salts↗
PubMed1991

Plasma membrane-bound carbonic anhydrase activity in the regenerating rat liver.

Part of the carbonic anhydrase activity of hepatocytes has been reported to be located in the plasma membrane. This strategic location suggests a physiological role other than that located within the cell and probably related to the specific secretory function of these cells. Furthermore, after two-thirds hepatectomy an enzymatic retrodifferentiation has been reported. We reasoned that liver regeneration probably affects the carbonic anhydrase activity in different ways depending upon its location and hence presumably physiological role. We measured, therefore, carbonic anhydrase activity in a soluble fraction or in a plasma membrane-enriched fraction obtained from liver homogenate from rats undergoing hepatectomy (two-thirds) one, three or seven days before liver resection and homogenation. No changes in carbonic anhydrase activity were found as far as soluble fraction was concerned. However, the carbonic anhydrase activity in plasma membrane was reduced (by 55%) soon after hepatectomy, there after it increased, returning to near control value at seven days. Lactate dehydrogenase activities in soluble and plasma membrane fractions were not modified by the regenerative process. Neither was 5'-nucleotidase activity determined in plasma membrane affected by liver regeneration. In summary, these results indicate a higher sensitivity of plasma membrane carbonic anhydrase activity to the regenerative process than soluble carbonic anhydrase activity. This suggests a different control of the turnover of these isoenzymes during rat liver regeneration. The phenomenon is consistent with a different physiological role for these activities; i.e., one (plasma membrane-bound carbonic anhydrase activity) may be involved in specific functions of differentiated hepatocytes, and another (soluble carbonic anhydrase activity) may be involved in general functions shared by both differentiated and undifferentiated cells.

Animals↗
PubMed1991

Bicarbonate-induced activation of taurocholate transport across the basal plasma membrane of human term trophoblast.

The efflux of [14C]taurocholate from previously loaded vesicles, obtained from basal plasma membrane of human trophoblast, was studied. Apparent Km (620 microM) and Vmax (1.79 nmol.min-1.mg protein-1) values were similar to those found in influx experiments (Marin et al., Gastroenterology 99: 1431-1438, 1990). Transmembrane gradients of both bicarbonate (100 mM) and unlabeled taurocholate (0.5 mM) accelerated [14C]taurocholate efflux. The bicarbonate-induced effect was not abolished by carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) and K(+)-valinomycin voltage clamp. Neither was it mimicked by 5,5'-dimethyloxazolidine 2,4-dione (DMO) or by other organic (taurine, glycine, lactate, or acetate) or inorganic (Cl-, SCN-, HPO24-, or SO24-) anions, and it was not sensitive to carbonic anhydrase inhibitors. No effect of bicarbonate was observed either in the absence of gradient or in the presence of a cis-directed gradient. Bicarbonate-induced transstimulation was related to an increase in the value for the apparent Vmax (+30%). Study of the stoichiometry suggests that the most probable coupling ratio is one, bicarbonate: taurocholate. In summary, these results provide evidence for the existence of a bicarbonate-driven anion exchange in the basal plasma membrane of the human term placental trophoblast.

Acetazolamide↗
PubMed1990

Bile acid transport by basal membrane vesicles of human term placental trophoblast.

The aim of this work was to investigate the first step in the vectorial translocation of bile acids from the fetus to the mother, which is the transfer across the basal (i.e., fetal-facing) plasma membrane of the trophoblast. Thus, the uptake of [14C]taurocholate by basal plasma membrane vesicles obtained from normal human term placentas was studied. Taurocholate retention into vesicles was studied using a rapid filtration technique that was modified to reduce the taurocholate binding to the filters and to the external surface of the vesicles. Using 100 mumol/L substrate, the membrane vesicles showed a temperature-dependent, Na(+)-independent transport of taurocholate into an osmotically reactive intravesicular space. The initial rate of taurocholate influx in the presence of 100 mmol/L KNO3 followed saturation kinetics (apparent Km for taurocholate = 670 +/- 128 mumol/L; Vmax = 1.86 +/- 0.28 nmol/mg protein.60 s at 37 degrees C). Over the 6.9-7.9 pH range neither internal nor external pH nor inward nor outward proton gradients affected the uptake of taurocholate. When the electrical potential difference across the basal membrane was manipulated by external anion replacement (Cl-, SCN-, SO4(2-), or NO3-) or by valinomycin-induced K(+)-diffusion potential (vesicle inside negative), taurocholate uptake was not significantly modified. Taurocholate uptake was cis-inhibited in the presence of 1 mmol/L glycocholate, 0.5 mmol/L 4,4'-diisothiocyanostilbene-2,2'-disulfonate and 0.5 mmol/L sulfobromophthalein. However, 1 mmol/L probenecid or 0.5 mmol/L p-aminohippurate had no effect. Moreover, preloading the vesicles with 100 mmol/L HCO3- (but not with 100 mmol/L Cl- or 50 mmol/L SO4(2-) induced a significant enhancement in the initial rate of taurocholate uptake. In summary, these findings provide strong evidence for the presence of an electroneutral transport system for taurocholate in the basal plasma membrane of human chorionic trophoblast. They also suggest that this is likely to be an anion-exchange system.

Basement Membrane↗
PubMed1990

K-channel blocking drugs induce histamine release and 45Ca uptake in isolated mast cells.

Histamine secretion and 45Ca uptake processes were studied in mast cells treated with four K+ channel blocking drugs in physiological saline and in media containing different ionic concentrations. Quinine, 4-aminopyridine and sparteine were effective as histamine-releasing agents when mast cells were incubated in physiologic saline solution. The dose-response profile obtained was in the range of 0.1-0.5 mM for quinine, 1-10 for 4-aminopyridine and 0.5-5 mM for sparteine and did not show significant differences between purified and unpurified mast cells. By contrast, tetraethylammonium (1-100 mM) did not induce histamine release. The presence of high K+ or Rb+ concentrations in the medium (Tris-K+ or Tris-Rb+, both at 150 mM) displaced the profile obtained to the right in cells stimulated with 4-aminopyridine or sparteine, but abolished histamine release induced by quinine. Additionally, all three K+ channel blockers increased 45Ca uptake in mast cells. The exact mechanism of the action of K+ channel blockers on mast cells is unknown. However, the fact that the drugs used were effective as histamine-releasing and 45Ca uptake promoters suggests both that mast cells might be endowed with a K+ channel activity and that the blockade of this should open certain calcium channels, leading to elevated intracellular Ca2+ levels which in turn activate mast cell secretion.

4-Aminopyridine↗
PubMed1989

Resting plasma membrane potential of rat peritoneal mast cells is set predominantly by the sodium pump.

Changes in the plasma membrane potential of two histamine-releasing cells, rat peritoneal mast cells and basophilic leukemia cells 2H3 (RBL 2H3), were recorded with the potential-sensitive dye bis-oxonol. For mast cells, the presence of ouabain or the absence of K+ increased the fluorescence intensity of bis-oxonol; gramicidin had no effect. For RBL 2H3 cells, the presence of ouabain and the absence of K+ also increased bis-oxonol fluorescence but gramicidin also increased it. These results show that the plasma membrane potential of RBL 2H3 cells is set, in part, by the activity of the Na+ pump and in part by the K+ conductance, while that of rat mast cells is set predominantly by the Na+ pump.

Animals↗
PubMed1988

Dual effect of dihydropyridines on 45Ca uptake induced by the K+ -channel blocker, 4-aminopyridin on mast cells.

The 1,4-dihydropyridines (DHP) are calcium antagonists and represent a new class of drugs which act by a selective inhibition of Ca++ influx through voltage-operated calcium channels. We report the effect of nifedipine (Bay A 1040), nisoldipine (Bay K 5552) and nitrendipine (Bay E 5009) on the histamine release and on the 45Ca uptake promoted by 4-aminopyridin in mast cells. These cells treated with DHP (10(-12)-10(-3) M) activated the secretory response in a dose-dependent manner in the range of concentrations 10(-6)-10(-3) M, whereas concentrations of 10(-12)-10(-6) M did not significantly inhibit the secretion. 4-Aminopyridin, a known K+ -channel blocker, induced 45Ca uptake. Pretreatment of mast cells with DHP prior to 4-aminopyridin stimulation inhibited or stimulated 45Ca uptake depending on concentration; thus, concentrations of DHP below 10(-12) of nitrendipine and 10(-9) for nisoldipine and nifedipine were inhibitory, while higher doses potentiated 45Ca uptake. These results demonstrate a diversity of pharmacological effects of DHP on mediator secretion and 45Ca uptake in mast cells and throw into question their only properties as Ca++ antagonists.

4-Aminopyridine↗
PubMed1988

[Effect of colchicine on histamine secretion and calcium uptake in mast cells].

The function of contractile system of microtubules on the mechanism of mast cell exocytosis by using colchicine, a depolymerizing alkaloid of the microtubular system, has been studied. The response of histamine release and 45Ca-uptake in isolated rat mast cells treated with colchicine has been determined. The incubation of mast cells in the presence of 10(-8)-10(-3) M colchicine slightly inhibits histamine secretion induced by the stimulant concentration 50 micrograms/ml of compound 48/80 (35 +/- 5%). Similarly colchicine does not significantly affect histamine values spontaneously elicited in unstimulated mast cells; the percentages of secretion are never greater than 10%. However, high doses of this alkaloid are found to markedly inhibit entry of calcium ions into the cell. These results suggest that microtubules do not participate in the secretory process of mast cells, although they significantly decrease calcium uptake. The microtubules might be connected to the membrane, so that the depolymerization of this contractile system could damage the membrane structures through which Ca2+ is transported.

Animals↗
PubMed1987

Valinomycin, a degranulating agent in rat mast cells which inhibits calcium-uptake.

The effect of valinomycin on both, mast cell histamine release and on calcium (45Ca)-uptake processes was examined. Pleural and peritoneal mast cells were purified in isotonic Percoll (pH = 7) and mixed populations were used in the experiments. Valinomycin (10(-9)-10(-5) M) stimulated histamine release in isolated rat mast cells when the incubation medium contained high K+ concentrations (Tris-K+ with 150 mM K+), but not in other media such as Tris-Na+ (120 mM Na+) or Tris-sucrose (300 mM sucrose). In contrast, in the absence of valinomycin, elevated K+ levels in the external environment did not activate mast cell secretion. Optimum response in valinomycin-treated mast cells was obtained when the cells were incubated for 60 min. Also valinomycin (10(-5) M) induced substantial inhibition of 45Ca-uptake while lower doses (10(-9)-10(-7) M) did not affect or only slightly increased uptake. In this paper valinomycin is shown to be a degranulating agent eliciting mediator release in mast cells incubated in the presence of high K+ levels, which does not require extracellular calcium and inhibits 45Ca uptake. The possibility that valinomycin acts as a K+ ionophore, as in other secretory systems, is discussed.

Animals↗
PubMed1987

Adrenergic activity on rat pleural and peritoneal mast cells. Loss of beta-receptors during the purification procedure.

Adrenergic agonists inhibit the release of histamine from rat pleural and peritoneal mast cells stimulated with compound 48/80 to a degree dependent on their beta-activity. Isoprenaline takes part in a stereoselective inhibitory action in the range 10(-7)-10(-4) M. Adrenaline induces a similar response pattern, with inhibition at higher concentrations. The response profile, but not the maximum values of inhibition, is clearly dependent on the concentration of the histamine releaser. Noradrenaline by itself is a histamine releaser, no stereoselectivity being observed. In the presence of compound 48/80 it takes part in a non-stereoselective inhibitory reaction at low concentrations. Inhibition of histamine release by isoprenaline was antagonized by 10 or 100 microM propranolol except at the highest isoprenaline concentration (1 mM). Both atenolol and propranolol nullified the inhibitory activity of noradrenaline, but not the increased histamine release it induces at higher concentrations (at least when acting in conjunction with compound 48/80). When rat mast cells are purified through Percoll, a change in their response profiles is observed. Isoprenaline and adrenaline by themselves elicit non-specific release of histamine; with compound 48/80, release is additive in the case of isoprenaline and supra-additive in the case of adrenaline. Results point to the loss of beta-adrenergic inhibitory activity after purification.

Animals↗
PubMed1987

Hydralazine-relaxing effect on rat aorta is not mediated through changes in ATPase activity.

Hydralazine, a hypotensive agent, induces relaxation on smooth musculature. Several mechanisms related to membrane processes have been proposed to explain its relaxing action. In the present paper, the effects of hydralazine on ATPase activity in rat aorta have been studied. Hydralazine (10(-4)-5 X 10(-3) M concentration-dependently relaxed the isolated rat aortic arterial strips under norepinephrine-, serotonin- and K+-contractures. 5-Hydroxytryptamine contractures were more sensitive to the effects of hydralazine than noradrenaline- and potassium-contractures. We found that hydralazine does not modify ATPase activity on rat aorta homogenates. On the other hand, ATPase activity of rat aorta homogenates is dependent on divalent cations Ca2+ and Mg2+, and a little Na, K-ATPase activity was found.

Adenosine Triphosphatases↗
PubMed1986

Effect of calcium on histamine release from pleural and peritoneal mast cells induced by catechol.

Histamine release from rat pleural and peritoneal mast cells induced by catechol (1, 10, 50, 250 microM and 1 mM) has been studied. The dose-response induced by catechol is non-cytotoxic, is not modified by purification of mast cells and is calcium independent. The sensitivity and maximum response to catechol is the same irrespective of the presence or absence of Ca++, except on purified pleural mast cells, that showed a plateau response at 250 microM catechol in the absence of Ca++, and on unpurified peritoneal mast cells which exhibited a lower maximum response equally in the absence of Ca++. The release is induced by catechol at concentrations as low as 50 microM in all cases, and the maximum response is reached at 1 mM.

Animals↗
PubMed1986

[Na+ K+ ATPase activity in mast cells from the pleural and peritoneal cavities of the rat].

ATPase activity in rat mast cells was studied, assuming that pleural and peritoneal mast cells are different populations. Mast cells were purified with Percoll. Enzymatic activity was found to be 36% higher in pleural cells that in peritoneal cells. Moreover, for both populations results show a Na+-K+ ATPase activity either low or slightly inhibited by ouabain.

Animals↗
PubMed1985

Difference in, and influence of the purification medium on, sensitivity and maximum response of peritoneal and pleural mast cells stimulated by certain polyamines.

The actions of the polyamines compound 48/80, poly-l-lysine and polymyxin B on rat pleural and peritoneal mast cell secretion have been studied. Unpurified pleural mast cells released more histamine than peritoneal mast cells when stimulated by submaximal concentrations of compound 48/80 and poly-l-lysine, but the same profile of response was observed with polymyxin B in both populations. Dose-response studies of peritoneal and pleural mast cells purified with Percoll and Ficoll and stimulated by polymyxin B showed a decreased sensitivity and decreased maximum response of peritoneal cells when Percoll was used. The maximal response of pleural cells and the sensitivity of peritoneal cells were affected only slightly by Ficoll.

Animals↗
PubMedDate not supplied

Expression of the beta-isoforms of Na,K-ATPase in the renal cortex of rats.

The aim of the present study was to assess the presence of beta1- and beta2-isoforms of the beta-subunit of Na,K-ATPase in the rat renal cortex. This has been accomplished by immunohistochemistry and Western blotting using isoform-specific antisera. Western blot of brain extract, used as positive control, revealed the bands corresponding to beta1- and beta2-glycosylated peptides, with a molecular weight (MW) of approximately 50-60 that, after exhaustive treatment with N-endoglycosidase-F, migrated to the MW corresponding to the core peptides (approximately 35). In the renal cortex, Western blot revealed the bands corresponding to beta1. After deglycosylation of the samples, the bands hybridizing with the anti-beta1-antibodies moved to the MW corresponding to a partially deglycosylated form and the core peptide. Bands with a MW of approximately 50-60 hybridized with anti-beta2, although digestion with endoglycosidase failed to move the band towards a lower MW. Immunohistochemistry revealed the presence of beta1- but not beta2-isoform. Northern blot for total mRNA showed strong signals for beta1 in renal cortex, the mRNA for the beta2-isoform being undetectable. In conclusion, only mRNA and glycopeptide of the beta1-isoform seem to be present in renal cortex of adult control rats.

Animals↗