Effect of preparations Methyure and Ivine on Са(2+)-ATPases activity in plasma and vacuolar membrane of corn seedling roots under salt stress conditions

Ca2+-ATPases regulate the functioning of Ca2+-dependent signaling pathway SOS which provides removal of Na+ from the cytoplasm of cells via Na+/H+-antiporters in saline conditions. The influence of synthetic preparations Methyure and Ivine on the Ca2+-ATPase activity was investigated. It was shown that exposition of corn seedlings in the presence of 0.1 M NaCl rather enhanced hydrolytic than transport activity of Ca2+-ATPases in plasma and vacuolar membrane of root cells. It was found that seed treatment with such preparations, especially Methyure, caused intensification of the both activities of Ca2+-ATPases, mainly in vacuolar membrane. The results indicate than salt protective activity of preparations, especially Methyure, is associated with increased Ca2+-ATPase activity, which regulates the functioning of Na+/H+-antiporters.

Secretory diarrhoea: mechanisms and emerging therapies

Diarrhoeal disease remains a major health burden worldwide. Secretory diarrhoeas are caused by certain bacterial and viral infections, inflammatory processes, drugs and genetic disorders. Fluid secretion across the intestinal epithelium in secretory diarrhoeas involves multiple ion and solute transporters, as well as activation of cyclic nucleotide and Ca(2+) signalling pathways. In many secretory diarrhoeas, activation of Cl(-) channels in the apical membrane of enterocytes, including the cystic fibrosis transmembrane conductance regulator and Ca(2+)-activated Cl(-) channels, increases fluid secretion, while inhibition of Na(+) transport reduces fluid absorption. Current treatment of diarrhoea includes replacement of fluid and electrolyte losses using oral rehydration solutions, and drugs targeting intestinal motility or fluid secretion. Therapeutics in the development pipeline target intestinal ion channels and transporters, regulatory proteins and cell surface receptors. This Review describes pathogenic mechanisms of secretory diarrhoea, current and emerging therapeutics, and the challenges in developing antidiarrhoeal therapeutics.

[Effect of adaptogenic preparations on Na+/H+-antiporter function in plasma membrane of corn root cells under salinity conditions]

Salinity is a hard stress factor for plant organisms which negative effect is caused chiefly by sodium toxic for plants. Plant cells try to remove Na+ from their cytoplasm outside and to vacuolar space by secondary active Na+/H+-antiporters. Their functions can be intensified by gene engineering methods however we try do it with the help of non-toxic bioactive preparations. A comparison of their effect on the plasma membrane of Na+/H+-antiporters was carried out on corn seedling roots of Zea mays L. exposed at 0.1 M NaCl. Before we have established that Methyure used by seed pretreating possesses a high salt protective ability as against Ivine. It was found that without NaCl exposition Na+/H+-antiporter activity in root plasma membrane was nearly unnoticeable but increased slightly with seedling age. Methyure and Ivine did not influence its activity in control root seedling. One day 0.1 M NaCl exposition evoked a considerable increasing of Na+/H+-antiporter activity and its gene expression but these effects disappeared at 10 day NaCl exposition. Methyure use reinforced Na+/H+-antiporter activity and prolonged it at NaCl exposition without effect on its gene expression whereas Ivine effects on these indexes were insignificant. Obtained results showed that the salt protective capability of Methyure is connected with plasma membrane Na+/H+-antiporter activation which is realized on molecular level.

[Usage of flavonoids for effective correction of functional and structural breaches of erythrocytes membranes during an extraordinary physical strain in experiments]

The effect of treatment course of bioflavonoids quercetin and diquertin on phospholipids and fatty acid composition of erythrocytes membranes and amilorid-dependent activity Na+/H+ transmembrane exchanger of erythrocytes have been studied in condition of chronic physical tension in mice in consequence of extraordinary running strain. The studied drugs actively prevented from the changes of chemical composition and as a result structural and functional changes of erythrocytes membranes. It is established that the studied bioflavonoids prevented from the development of extraordinary physical strain syndrome.

Luminal Na(+)/H (+) exchange in the proximal tubule

The proximal tubule is critical for whole-organism volume and acid-base homeostasis by reabsorbing filtered water, NaCl, bicarbonate, and citrate, as well as by excreting acid in the form of hydrogen and ammonium ions and producing new bicarbonate in the process. Filtered organic solutes such as amino acids, oligopeptides, and proteins are also retrieved by the proximal tubule. Luminal membrane Na(+)/H(+) exchangers either directly mediate or indirectly contribute to each of these processes. Na(+)/H(+) exchangers are a family of secondary active transporters with diverse tissue and subcellular distributions. Two isoforms, NHE3 and NHE8, are expressed at the luminal membrane of the proximal tubule. NHE3 is the prevalent isoform in adults, is the most extensively studied, and is tightly regulated by a large number of agonists and physiological conditions acting via partially defined molecular mechanisms. Comparatively little is known about NHE8, which is highly expressed at the lumen of the neonatal proximal tubule and is mostly intracellular in adults. This article discusses the physiology of proximal Na(+)/H(+) exchange, the multiple mechanisms of NHE3 regulation, and the reciprocal relationship between NHE3 and NHE8 at the lumen of the proximal tubule.

Epidermal growth factor and sphingosine-1-phosphate stimulate Na+/H+ exchanger activity in the human placental syncytiotrophoblast

The Na+/H+ exchanger (NHE) has a key role in intracellular pH ([pH]i) regulation of the syncytiotrophoblast in the human placenta and may have a role in the life cycle of this cell. In other cells the NHE (actually a family of up to 9 isoforms) is regulated by a variety of factors, but its regulation in the syncytiotrophoblast has not been studied. Here, we tested the hypotheses that EGF and sphingosine-1-phosphate (S1P), both of which affect trophoblast apoptosis and, in other cell types, NHE activity, stimulate syncytiotrophoblast NHE activity. Villous fragments from term human placentas were loaded with the pH-sensitive dye, BCECF. NHE activity was measured by following the recovery of syncytiotrophoblast [pH]i following an imposed acid load, in the presence and absence of EGF, S1P, and specific inhibitors of NHE activity. Both EGF and S1P caused a dose-dependent upregulation of NHE activity in the syncytiotrophoblast. These effects were blocked by amiloride 500 microM (a nonspecific NHE blocker) and HOE694 100 microM (NHE blocker with NHE1 and 2 isoform selectivity). Effects of EGF were also reduced by the NHE3 selective blocker S3226 (used at 1 microM). These data provide the first evidence that both EGF and S1P stimulate NHE activity in the syncytiotrophoblast; they appear to do so predominantly by activating the NHE1 isoform.

Restoration of osmotically inhibited twitch force in rat cardiac trabeculae: role of Na+-H+ exchange

1. When rat cardiac muscle is subjected to an increase of osmolality, its peak twitch force is immediately inhibited. Subsequently, over a period of several minutes, twitch force undergoes restoration, the extent of which is determined by the osmolality. The aim of the present study was to determine the factors that contribute to this restorative phenomenon. 2. Trabeculae were isolated from the right ventricles of rat hearts and mounted in an organ bath at 37 degrees C. The osmolality of the bathing solution was increased by 100 mOsmol (to 400 mOsmol) by the addition of various proportions of NaCl and sucrose while recording twitch force production. The role of Na+-H+ exchange in restoring twitch force was examined by use of the specific inhibitor cariporide (HOE 642). The role of Na+-Ca2+ exchange was examined by reducing [Ca2+]o (from 2 mmol/L to 0.5 mmol/L) or by substituting LiCl for NaCl. 3. Cariporide (25 micro mol/L) completely abolished twitch force restoration, thereby implicating a central role for the Na+-H+ exchanger. At constant [Na+]o, the extent of restoration was [Ca2+]o dependent, suggesting an independent contribution by the Na+-Ca2+ exchanger. This suggestion was supported by the finding that Li+, which substitutes for Na+ on the Na+-H+ exchanger, but not on the Na+-Ca2+ exchanger, also reduced the extent of restoration of hyperosmotically inhibited twitch force. 4. We conclude that the immediate inhibition of peak twitch force of rat cardiac muscle by hyperosmotic solutions reflects, in part, elevation of [H+]i, subsequent to reduction of cell volume. Hyperosmotic activation of Na+-H+ exchange then progressively relieves the inhibitory effect of protons on force development. The accompanying increase in [Na+]i in turn enhances Ca2+ influx on the Na+-Ca2+ exchanger, with the result that twitch force undergoes further restoration.

Alkalization produced by high-dose carbachol in HSG cell line is independent of Ca2+

OBJECTIVES

The aim of this investigation was to clarify the mechanism of alkalization induced by carbachol in HSG cells.

MATERIALS AND METHODS

Cells of the HSG cell line derived from a human submandibular gland adenocarcinoma and those of the A-431 human epidermoid carcinoma cell line were loaded with a fluorescent pH indicator, BCECF/AM, and the change in the intracellular pH of adherent cells and suspended ones were measured following stimulation with various concentrations (10(-7) M to 10(-2) M) of neurotransmitters (carbachol, noradrenaline, and isoproterenol).

RESULTS

Isoproterenol did not cause alkalization of either cell type, whereas, noradrenaline and carbachol alkalized both types over the concentration ranges of 10(-6) M to 3 x 10(-3) M (HSG cell by noradrenaline), 10(-7) M to 2 x 10(-4) M (A-431 cell by noradrenaline), and 7 x 10(-5) M to 10(-4) M (A-431 cell by carbachol). On the other hand, alkalization induced by carbachol in the HSG cells was recognized at concentrations higher than 6 x 10(-5) M, and it showed no upper limit in terms of carbachol concentration. This high-dose carbachol alkalization was not eliminated by preincubation with nifedipine (100 microM), a Ca2+ channel blocker, or with thapsigargin (100 microM), a microsomal Ca(2+)-ATPase inhibitor.

CONCLUSIONS

The alkalization system induced by carbachol in the HSG cell was quite different from that in the A-431 cell, and that induced by high-dose carbachol in HSG cells appeared to be independent of intracellular Ca2+. These findings will be useful to clarify the mechanism of salivary secretion stimulated by neurotransmitters.

The role of Na+/H+ exchange and growth factors in pulmonary artery smooth muscle cell proliferation

Chronic hypoxia produces pulmonary hypertension, in part because of hypertrophy and hyperplasia of pulmonary artery smooth muscle cells (PA SMC). Platelet-derived growth factor (PDGF) and epidermal growth factor (EGF) have been shown to stimulate SMC proliferation and may be involved in these vascular changes. Both factors cause a rise in intracellular pH (pHi) in systemic vascular SMC through stimulation of the Na+/H+ exchanger, an event that has been thought to be permissive, allowing cell proliferation in response to the growth factor. The present studies examined the possibility that the activation of Na+/H+ exchange is involved in the PA SMC mitogenic response to these growth factors. Na+/H+ exchange activity was assessed by monitoring pHi in cultured cells using the pH-sensitive dye, 2'7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). PDGF (60 ng/ml) exposure led to a marked activation of Na+/H+ exchange, evidenced by a rise in pHi (mean +/- SEM) of 0.20 +/- 0.03 pH units (n = 5, P < 0.05). EGF (60 ng/ml) exposure produced a rise in pHi of 0.27 +/- 0.03 pH units (n = 5, P < 0.05). Dimethyl amiloride (DMA, 50 microM), a competitive inhibitor of Na+/H+ exchange, blocked the pH response to PDGF and EGF. PA SMC showed a proliferative response when exposed to PDGF and EGF which was attenuated by 50 microM DMA (n = 6). Thus, activation of the Na+/H+ exchanger may be important in pulmonary cell signaling in response to growth factors as it has been found to be in systemic vessels.

Induction of alkalinization in cultured renal cells (MDCK line) by prostaglandin E2

The effect of prostaglandin E2 (PGE2), on the intracellular pH (pHi) in BCECF-loaded Madin Darby Canine Kidney (MDCK) cells was investigated. PGE2 elevated the pHi. Under resting conditions, pHi of MDCK cells suspended in PBS at pH 7.4 was 7.11 +/- 0.08; PGE2 increased pHi with an EC50 of 0.16 microM. PGF2 alpha elicited a similar response to PGE2, with an EC50 of 0.24 microM. Amiloride (0.4 mM) reversed the response to PGE2 (control 7.18 +/- 0.05; PGE2 7.26 +/- 0.05; after amiloride 7.18 +/- 0.05). In MDCK cells exposed to a Na(+)-free solution, alkalinization induced by this eicosanoid was blocked (Ringer-choline 7.16 +/- 0.03; PGE2 7.16 +/- 0.02). PGE2 increased by 100% the rate of recovery after an acidification pulse with ammonium chloride. In the presence of Ringer-HCO3- (pH 7.4), there was a delay in the maximal response to this prostaglandin (PBS 2.2 +/- 0.27, Ringer-bicarbonate 3.4 +/- 0.55 min) and the pHi increment was less marked than in PBS (0.09 pH units in HCO3- versus 0.16 pH units in PBS; P < 0.001). This effect of PGE2 was not blocked by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (1.0 mM). PMA (100 nM), activator of protein kinase C, mimicked the response to PGE2, suggesting the participation of this kinase on the effect of the prostanoid. As expected, two inhibitors of protein kinase C, staurosporine and sphingosine, abolished the response to PGE2. Staurosporine (0.10 microM), an inhibitor of protein kinase C, blocked the response to PGE2 (control 7.02 +/- 0.04; PGE2 and staurosporine 7.03 +/- 0.04, n = 9, not significant). Sphingosine, another inhibitor of protein kinase C, also blocked the response to PGE2. Two analogues of cAMP did not modify the pHi. In summary, PGE2 induced an intracellular alkalinization via stimulation of a Na+/H+ exchanger, with the participation of protein kinase C, in MDCK cells.