Role of the Na+/K+-ATPase in regulating the membrane potential in rat peritoneal mast cells

Potassium bromate (KBrO3) modulates oxidative stress and inflammatory biomarkers in sodium hydroxide (NaOH) - induced Crohn's colitis in Wistar rats

Potassium bromate (KBrO₃) present in consumed ozonised water was recently documented to exacerbate experimental gastric ulcer. Information, however, is vague as regards its effects in the colon where water reabsorption occurs. In this study, we observed the possible effects of KBrO₃ on oxidative stress and inflammatory biomarkers in sodium hydroxide (NaOH) - induced Crohn's colitis (CC). Wistar rats (180-200 g) were divided into six groups (n = 10): (i) control; (ii) untreated CC (induced by 1.4% NaOH; intra-rectal administration); and (iii-vi) CC treated with vitamin E, KBrO₃, vitamin E+KBrO₃, and sulphazalazine, respectively, for 7 days. Body weight and stool score were monitored daily. By day 3 and 7, excised colon was evaluated for ulcer scores and biochemical and histological analysis. Blood samples collected on days 3 and 7 were assayed for haematological indices using standard methods. Data were subjected to analysis of variance (ANOVA) and p ≤ 0.05 considered significant. Platelet/lymphocyte ratio, colonic ulcer score, malondialdehyde, and mast cells were significantly decreased while colonic sulfhydryl, and Ca²⁺- and Na⁺/K⁺-ATPase activities were increased following KBrO₃ treatment compared with untreated CC. These findings suggest that KBrO₃ may mitigate against NaOH-induced CC via inhibiting mast cell population and oxidative and inflammatory content but stimulating colonic sulfhydryl and Ca²⁺- and Na⁺/K⁺-ATPase activities.

Cell volume regulation in chondrocytes

Chondrocytes are the cells within cartilage which produce and maintain the extracellular matrix. Volume regulation in these cells is vital to their function and occurs in several different physiological and pathological contexts. Firstly, chondrocytes exist within an environment of changing osmolarity and compressive loads. Secondly, in osteoarthritic joint failure, cartilage water content changes and there is a notable increase in chondrocyte apoptosis. Thirdly, endochondral ossification requires chondrocyte swelling in association with hypertrophy. Regulatory volume decrease (RVD) and regulatory volume increase (RVI) have both been observed in articular chondrocytes and this review focuses on the mechanisms identified to account for these. There has been evidence so far to suggest TRPV4 is central to RVD; however other elements of the pathway have not yet been identified. Unlike RVD, RVI appears less robust in articular chondrocytes and there have been fewer mechanistic studies; the primary focus being on the Na(+)-K(+)-2Cl(-) co-transporter. The clinical significance of chondrocyte volume regulation remains unproven. Importantly however, transcript abundances of several ion channels implicated in volume control are changed in chondrocytes from osteoarthritic cartilage. A critical question is whether disturbances of volume regulation mechanisms lead to, result from or are simply coincidental to cartilage damage.

Expression of Na(+)/K(+)-ATPase alpha subunit isoforms in rat salivary glands: occurrence of sense and antisense RNAs of the alpha3 isoform in the sublingual gland

We examined the expression of Na(+)/K(+)-ATPase alpha-subunit isoforms in rat salivary glands by RT-PCR. Isoform alpha1 was expressed strongly in all three major salivary glands. The alpha2 isoform was expressed in both submandibular gland (SMG) and sublingual gland (SLG) but faintly in the parotid gland (PG). The alpha3 was detected only in the SLG, and the alpha3 mRNA in the SLG was 1/8 of its level in the brain. Na(+)/K(+)-ATPase alpha3 isoform in the SLG, was localized predominantly on the basolateral plasma membranes in serous cells by immunohistochemical method. We also found the presence of natural antisense RNA of the alpha3 isoform in rat SLG: the 1st-strand cDNA prepared with gene-specific forward primers targeted to the CDS region and to the promoter region of the alpha3 gene in place of oligo(dT) or gene-specific reverse primers produced reasonable PCR products corresponding to the alpha3 cDNA sequence by the subsequent PCR reaction. Synthesis of the 1st-strand cDNA with the gene-specific forward primers was prevented by RNase digestion of the total RNA preparation, indicating that the PCR products in the RT-PCR system were not due to the contaminated genomic DNA, if any. The alpha3 protein level in rat SLG increased with aging, and levels of both alpha3 mRNA (sense RNA) and alpha3 antisense RNA were higher in SLGs of aged rats than in those of young rats, respectively.

Calcium-pH Crosstalks in the human mast cell line HMC-1: Intracellular alkalinization activates calcium extrusion through the plasma membrane Ca2+-ATPase

The human mast cell line (HMC-1) has been used to study the relationship between intracellular pH and cytosolic calcium (Ca2+) in mast cells. Thapsigargin (TG) caused store-operated Ca2+ entry, that is enhanced by the PKC activator PMA. NH4Cl-induced alkalinization showed an inhibitory effect on TG-sensitive stores depletion (not on TG-insensitive stores), and also on final cytosolic Ca2+ levels reached in response to both TG and the ionophore ionomycin. Loperamide, a positive modulator of store-operated channels, induced a slight Ca2+ entry by itself, and also increased TG-induced Ca2+ entry. This enhancement was not enough to reverse the inhibitory effect of NH4Cl-induced alkalinization. When comparing the effect of NH4Cl-induced alkalinization on Ca2+ levels, with those observed using Ca2+ channel blockers (namely Ni2+ and SKF-96365), cytosolic profiles for this ion are different, either in modified saline solution or in HCO3(-)-free medium. Thus, it seems unlikely that the inhibitory effect of NH4Cl-induced alkalinization on Ca2+ is taking place by blockage of Ca2+ entry. Furthermore, inhibition of the plasma membrane Ca2+-ATPase (an important mechanism for Ca2+ efflux) with sodium orthovanadate (SO) matches with the inhibition of the negative effect on Ca2+ levels elicited by NH4Cl. Data indicate that NH4Cl-induced alkalinization might be activating Ca2+ efflux from the cell, by stimulation of the plasma membrane Ca2+-ATPase, and also confirm our previous finding that Ca2+ is a secondary signal to activate HMC-1 cells.

Calcium-pH crosstalks in rat mast cells: modulation by transduction signals show non-essential role for calcium in alkaline-induced exocytosis

Alkalinization of cytosolic pH with ammonium chloride (NH4Cl) was reported to be a stimulus for mast cell degranulation. This paper studied the modulatory role of drugs that target protein kinase C (PKC), adenosine 3',5'-cyclic monophosphate (cAMP), tyrosine kinase (TyrK) and phosphatidylinositol 3-kinase (PI3K) on this effect. We used Go6976 (100 nM) and low concentrations of GF109203X (Gf) (50 nM) to inhibit calcium-dependent PKC isozymes. For calcium-independent isozymes, we used 500 nM Gf, and 10 microM rottlerin to specifically inhibit PKC delta, and chelerythrine as non-specific PKC inhibitor. Genistein (10 microM) and lavendustin A (1 microM) were used as unspecific TyrK inhibitors, and 10 nM wortmannin as a PI3K inhibitor. Chelerythrine and 50 nM Gf inhibit histamine release in the presence of external calcium. The inhibition caused by wortmannin was strictly internal calcium-dependent. cAMP-active drugs did not modify the response to NH4Cl. The effect of NH4Cl on histamine release was triggered by a transient elevation on cytosolic pH, which was simultaneous to an elevation on cytosolic calcium and followed by a probable Ca2+-H+ exchange after addition of external calcium. EGTA inhibit the response to suboptimal concentrations of NH4Cl, and BAPTA increased the effect of NH4Cl. There is a clear relationship between NH4Cl-mediated calcium release and histamine release, since those drugs that inhibit this release also inhibit NH4Cl-mediated histamine release; nevertheless, NH4Cl-mediated histamine release was possible in the absence of any calcium release, as shown with BAPTA. This data, in combination with the results with PKC inhibitors, suggest that calcium is not only unnecessary to trigger cell activation, but also that it may be a negative modulator of NH4Cl-mediated exocytosis.

Inhibition of the antigen-induced activation of RBL-2H3 cells by charybdotoxin and cetiedil

Quinidine and Ba(2+), non-selective K(+)-channel blockers, have previously been shown to inhibit antigen-induced mediator (beta-hexosaminidase) release from RBL-2H3 cells, a mucosal-type mast cell line. We therefore used selective blockers of Ca(2+)-activated and other K(+) channels to determine if there was a role for these channels in antigen-induced mediator release. Charybdotoxin and cetiedil dose-dependently inhibited beta-hexosaminidase release with IC(50) values of 133 nM and 84 microM, respectively. Charybdotoxin also inhibited the repolarization phase of the antigen-induced biphasic change in the membrane potential (IC(50) 84 nM), antigen-stimulated 86Rb(+)-efflux and increase in free intracellular calcium, [Ca(2+)](i). Iberiotoxin, margatoxin, apamin and tetraethylammonium had no effect on beta-hexosaminidase release. These results suggest that K(+) conductances play a significant role in mediator release from RBL-2H3, that these conductances are of the intermediate conductance Ca(2+)-activated K(+) channel (IK(Ca)) type, and that they are somewhat similar to those which have been described in red blood cells, though they are much less sensitive to clotrimazole.

Free radicals: key to brain aging and heme oxygenase as a cellular response to oxidative stress

Aging is one of the unique features in all organisms. The impaired functional capacity of many systems characterizes aging. When such impairments occur in the brain, the susceptibility to neurodegenerative diseases amplifies considerably. The free radical theory of aging posits that the functional impairments in brains are due to the attack on critical cellular components by free radicals, reactive oxygen species, and reactive nitrogen species produced during normal metabolism. In this review, we examine this concept based on the parameters of oxidative stress in correlation to aging. The parameters for lipid peroxidation are phospholipid composition, reactive aldehydes, and isoprostanes. The parameters for protein oxidation are protein carbonyl levels, protein 3-nitrotyrosine levels, electron paramagnetic resonance, and oxidative stress-sensitive enzyme activities. We conclude that free radicals are, at least partially, responsible for the functional impairment in aged brains. The aging brain, under oxidative stress, responds by induction of various protective genes, among which is heme oxygenase. The products of the reaction catalyzed by heme oxygenase, carbon monoxide, iron, and biliverdin (later to bilirubin) each have profound effects on neurons. Although there may be other factors contributing to brain aging, free radicals are involved in the damaging processes associated with brain aging, and cellular stress response genes are induced under free radical oxidative stress. Therefore, this review supports the proposition that free radicals are, indeed, a key to brain aging.

Role of the heme oxygenases in abnormalities of the mesenteric circulation in cirrhotic rats

Carbon monoxide (CO), a product of heme metabolism by heme-oxygenase (HO), has biological actions similar to those of nitric oxide (NO). The role of CO in decreasing vascular responses to constrictor agents produced by experimental cirrhosis induced by carbon tetrachloride was evaluated before and after inhibition of HO with tin-mesoporphyrin (SnMP) in the perfused superior mesenteric vasculature (SMV) of cirrhotic and normal rats and in normal rats transfected with the human HO-1 (HHO-1) gene. Perfusion pressure and vasoconstrictor responses of the SMV to KCl, phenylephrine (PE), and endothelin-1 (ET-1) were decreased in cirrhotic rats. SnMP increased SMV perfusion pressure and restored the constrictor responses of the SMV to KCl, PE, and ET-1 in cirrhotic rats. The relative roles of NO and CO in producing hyporeactivity of the SMV to PE in cirrhotic rats were examined. Vasoconstrictor responses to PE were successively augmented by stepwise inhibition of CO and NO production, suggesting a complementary role for these gases in the regulation of reactivity of the SMV. Expression of constitutive but not of inducible HO (HO-1) was increased in the SMV of cirrhotic rats as was HO activity. Administration of adenovirus containing HHO-1 gene produced detection of HHO-1 RNA and increased HO activity in the SMV within 7 days. Rats transfected with HO-1 demonstrated reduction in both perfusion pressure and vasoconstrictor responses to PE in the SMV. We propose that HO is an essential component in mechanisms that modulate reactivity of the mesenteric circulation in experimental hepatic cirrhosis in rats.

Evidence against the functional involvement of outwardly rectifying Cl- channels in agonist-induced mast cell exocytosis

In isolated rat peritoneal mast cells, an outwardly rectifying Cl- channel has been described. Influx of Cl- through this Cl- channel (I(Cl-(OR)) causes hyperpolarization, which facilitates Ca2+ currents through store-operated Ca2+ channels. The exocytotic effect of nerve growth factor (NGF) in the presence of lyso-phosphatidylserine strictly depends on the presence of extracellular [Ca2+]o. The aim of the present study was to assess the importance of I(Cl-(OR)) for exocytosis induced by NGF/lyso-phosphatidylserine. Therefore, we investigated the effects on NGF/lyso-phosphatidylserine-induced exocytosis of [3H]5-hydroxytryptamine ([3H]5-HT) in rat peritoneal mast cells: (a) of two inhibitors of I(Cl-(OR)) (4,4'-diisothiocyanatostilbene2,2'-disulfonic acid [DIDS] and diethylstilbestrol), and (b) of replacement of extracellular Cl- by methylsulfate. Additionally, whole-cell patch-clamp experiments (nystatin-perforated patch) were performed. Diethylstibestrol and DIDS, in concentrations sufficient to abolish the I(Cl-(OR)) (10 microM) and the replacement of (Cl-)o by methylsulfate, were ineffective in impairing the NGF/lyso-phosphatidylserine-induced [3H]5-HT-release. These findings argue against a role of outwardly rectifying Cl- channels in exocytosis induced by NGF/lyso-phosphatidylserine in rat peritoneal mast cells.

Ouabain-induced enhancement of rat mast cells response. Modulation by protein phosphorylation and intracellular pH

The digitalic glicoside ouabain induces potentiation of rat mast cell histamine release in response to several stimuli, which is mediated by Na+/Ca2+ exchanger. In this work, we studied the effect of ouabain on cytosolic calcium, intracellular pH and histamine release with Ca2+ ionophore A23187 in conditions designed to maximize ouabain-induced potentiation of rat mast cells response. The effect of protein kinase C (PKC), cAMP and phosphatase inhibition was also tested. Ouabain induced an enhancement in histamine release, cytosolic calcium and intracellular pH. The adenylate cyclase activator forskolin reduced the effect of ouabain on histamine release and intracellular pH, but enhanced the effect on cytosolic calcium. PKC activator PMA enhanced the effect of ouabain on histamine release and cytosolic calcium, without affecting intracellular pH. A PKC inhibitor, GF-109203X, reduced ouabain-induced enhancement of histamine release and intracellular pH, but increased the enhancement on cytosolic calcium. Finally, inhibition of protein phosphatases 1 and 2A with okadaic acid, increased the effect of ouabain on histamine release and intracellular pH, but reduced cytosolic calcium in presence of ouabain. This result suggest that ouabain-induced potentiation of rat mast cell histamine release with A23187 is modulated by kinases, and this modulation may be carried out by changes in intracellular alkalinization. However, the mechanism underlying cellular alkalinization remains to be elucidated.

Sodium-potassium-ATPase electrogenicity in cerebral precapillary arterioles

Electrogenicity of the Na(+)/K(+) pump has the capability to generate a large negative membrane potential independently of ion-channel current. The high background membrane resistance of arterioles may make them susceptible to such an effect. Pump current was detected by patch-clamp recording from smooth muscle cells in fragments of arterioles (diameter 24-58 microm) isolated from pial membrane of rabbit cerebral cortex. The current was 20 pA at -60 mV, and the extrapolated zero current potential was -160 mV. Two methods of estimating the effect of pump electrogenicity on resting potential indicated an average contribution of -35 mV. In 20% of the recordings, block of inward rectifier K(+) channels by 10-100 microM Ba(2+) led to a small depolarization, but hyperpolarization was a more common response. Ba(2+) also inhibited depolarization evoked by 20 mM K(+). In arterioles within intact pial membrane, Ba(2+) failed to evoke constriction but inhibited K(+)-induced constriction. The data suggest that cerebral arterioles are vulnerable to the hyperpolarizing effect of the Na(+)/K(+) pump, excessive effects of which are prevented by depolarizing inward rectifier K(+) current