Dose-dependent lipid peroxidation induction on ex vivo intestine tracts exposed to chyme samples from fumonisins contaminated corn samples.

Fumonisins (FBs), Fusarium mycotoxins common food contaminant, are a potent inducer of oxidative stress and lipid peroxidation in intestinal cells. In order to verify this toxic effect in intestine tract, the aim was to assess lipid peroxidation (as malondialdehyde MDA increased levels) on intestine rat samples exposed to chyme samples from in vitro digestion of FBs contaminated corn samples. Naturally (9.61±3.2 µg/gr), artificially (726±94 µg/gr) and spiked corn samples at EU permitted FBs levels were digested and added to luminal side of Ussing chamber for 120 min. Fumonisins-free corn sample was used as control. The MDA increase was observed just in 83% of intestine samples exposed at EU FBs levels and the digestion process seems to reduce this incidence (50% of samples). Malondialdehyde levels were FBs dose- and subject-related and ranged from 0.07±0.01 to 3.59±0.6 nmol/mg. Highest incidence and MDA % increment (I) were found when intestine tracts were exposed to chymes from artificially corn sample. The induction of lipid peroxidation induced by FBs could be due to interactions between FBs and intestinal membranes, with consequent modifications in membrane permeability and oxygen diffusion-concentration, as suggested by other authors.

Influence on functional parameters of intestinal tract induced by short-term exposure to fumonisins contaminated corn chyme samples.

The gut is a possible target toward mycotoxin fumonisins (FBs) exposure. The study aims to investigate the effects induced by FBs contaminated-corn chyme samples on functional parameters of human and rat intestine by using Ussing chamber. Fumonisins-contaminated corn and processed corn samples were undergone to in vitro digestion process and then added to luminal side. A reduction (about 90%) of short circuit current (Isc µA/cm(2)) during exposure of human colon tissues to fumonisins-free corn chyme samples was observed, probably related to increased chyme osmolality. This hyperosmotic stress could drain water towards the luminal compartment, modifying Na(+) and Cl(-) transports. The presence of FBs in corn chyme samples, independently to their concentration, did not affect significantly the Isc, probably related to their interference towards epithelial Na(+) transport, as assessed by using a specific inhibitor (Amiloride). The rat colon tract represents a more accessible model to study FBs toxicity showing a similar functional response to human. In the rat small intestine a significant reduction (about 15%) of Isc parameter during exposure to uncontaminated or FBs contaminated corn chyme samples was observed; therefore such model was not suitable to assess the FBs toxicity, probably because the prevalent glucose and amino acids electrogenic absorption overwhelmed the FBs influence on ionic transport.

Sphingomyelin protects against apoptosis and hyperproliferation induced by deoxycholate: potential implications for colon cancer.

High fecal deoxycholate levels may promote colonic cancer. Phospholipids protect against bile salt-induced cytotoxicity. We therefore aimed to examine whether the dietary phospholipid sphingomyelin could decrease hyperproliferation induced by deoxycholate. In CaCo2 cells, hyperproliferation (by bromodeoxyuridine assay), phosphorylation state of cellular proteins, and apoptosis with concomitant caspase-3 activity were evaluated after incubation with 50-500 microM deoxycholate, with or without sphingomyelin. At 2 and 4 hr of incubation, deoxycholate induced dose-dependent apoptosis, with concomitant caspase-3 activation. At 16 hr, apoptosis had decreased markedly, but there was dose-dependent hyperproliferation (with changed phosphorylation status of cellular proteins) at this time point. Sphingomyelin dose-dependently reduced deoxycholate-induced apoptosis and hyperproliferation. In conclusion, sphingomyelin reduces deoxycholate-induced hyperproliferation and apoptosis. These findings may have implications for colonic cancer prevention by dietary modification.

Helicobacter pylori cytotoxin VacA increases alkaline secretion in gastric epithelial cells.

Human infection by the bacterium Helicobacter pylori (Hp) may lead to severe gastric diseases by an ill-understood process involving several virulence factors. Among these, the cytotoxin VacA is associated with higher tissue damage. In this study, the isolated frog stomach model was used to characterize the acute effects of VacA on the gastric epithelium. Our results show that VacA partially inhibits gastric acid output by increasing HCO(3)(-) efflux. Experiments conducted with double-barrelled pH or Cl(-)-selective microelectrodes on surface epithelial gastric cells (SECs) and single gastric glands show that VacA does not impair the activity of the oxyntic cells but renders the apical membrane of SECs more permeable to HCO(3)(-) and Cl(-). Inhibition of this permeation by 5-nitro-2-(3-phenylpropylamino) benzoic acid indicates that this may be due to the formation of anion-selective pores by the toxin. We suggest that VacA-dependent HCO(3)(-) efflux from SECs improves the environmental conditions (pH, CO(2) concentration) of the niche parasitized by Hp, that is the gastric surface. This may favor Hp persistence in the tissue and the secondary development of a chronic inflammation.

Asymmetrical, agonist-induced fluctuations in local extracellular [Ca(2+)] in intact polarized epithelia.

We recently proposed that extracellular Ca(2+) ions participate in a novel form of intercellular communication involving the extracellular Ca(2+)-sensing receptor (CaR). Here, using Ca(2+)-selective microelectrodes, we directly measured the profile of agonist-induced [Ca(2+)]ext changes in restricted domains near the basolateral or luminal membranes of polarized gastric acid-secreting cells. The Ca(2+)-mobilizing agonist carbachol elicited a transient, La(3+)-sensitive decrease in basolateral [Ca(2+)] (average approximately 250 microM, but as large as 530 microM). Conversely, carbachol evoked an HgCl2-sensitive increase in [Ca(2+)] (average approximately 400 microM, but as large as 520 microM) in the lumen of single gastric glands. Both responses were significantly reduced by pre-treatment with sarco-endoplasmic reticulum Ca(2+) ATPase (SERCA) pump inhibitors or with the intracellular Ca(2+) chelator BAPTA-AM. Immunofluorescence experiments demonstrated an asymmetric localization of plasma membrane Ca(2+) ATPase (PMCA), which appeared to be partially co-localized with CaR and the gastric H(+)/K(+)-ATPase in the apical membrane of the acid-secreting cells. Our data indicate that agonist stimulation results in local fluctuations in [Ca(2+)]ext that would be sufficient to modulate the activity of the CaR on neighboring cells.

Effects of rhythm regularization and rate control in improving left ventricular function in atrial fibrillation patients undergoing atrioventricular nodal ablation.

OBJECTIVES: To assess the relative contributions of rate control and rhythm regularization to left ventricular function in atrial fibrillation (AF) patients undergoing atrioventricular nodal ablation. This was performed by assessing the effect of ventricular rhythm regularization on left ventricular function during AF, and the effect of varying heart rate on left ventricular function after ablation. PATIENTS AND METHODS: Eleven patients with continuous AF and V/VI-R pacemakers undergoing therapeutic atrioventricular nodal ablation were studied. Preablation patients underwent two 30 min observation periods in a randomized, blinded fashion during which they were either in baseline AF (pacer set to default V/VI 50/min) or being paced using a rhythm stabilizing algorithm (RSA) designed to regularize rhythm without changing baseline ventricular rate. Six weeks after ablation, patients were again observed during the two following 30 min periods: pacing at a low clinically indicated rate (69+/-9 beats/min), and pacing at the rapid, mean preablation rate. During all observation periods, left ventricular function was measured continuously using a nuclear vest that provided validated measures of heart rate, ejection fraction, and normalized end-systolic volume (ESV) and end-diastolic (EDV) volume. RESULTS: Before ablation, RSA successfully regularized rhythm, decreasing the coefficient of variation of interbeat intervals 20+/-5% to 10+/-4% (P<0.001). The heart rate with RSA (105+/-19 beats/min) was not significantly different from the baseline AF rate (102+/-21 beats/min). Increased rhythm regularity achieved by RSA significantly improved left ventricular function, decreasing ESV from 62+/-12 units to 57+/-11 units (P=0.03), and increasing the ejection fraction from 31+/-11% to 36+/-11% (P=0.03). After ablation, at the clinically indicated low pacing rate of 69+/-9 beats/min, a much greater improvement in ejection fraction was observed, increasing to 44+/-13% (P=0.005 compared with preablation). However, rapid regular pacing at the mean preablation rate of 110+/-18 beats/min eradicated this improvement, decreasing the ejection fraction to 31+/-8% (P=0.003), and increasing ESV from 53+/-13 units to 62+/-8 units (P=0.006). CONCLUSIONS: Rhythm regularity achieved by a regularizing pacing algorithm can significantly, albeit modestly, improve left ventricular function in AF. However, more marked improvements in left ventricular function seen after ablation are primarily due to rate reduction alone.

Activation of A(3) adenosine receptor induces calcium entry and chloride secretion in A(6) cells.

We have previously demonstrated that in A(6) renal epithelial cells, a commonly used model of the mammalian distal section of the nephron, adenosine A(1) and A(2A) receptor activation modulates sodium and chloride transport and intracellular pH (Casavola et al., 1997). Here we show that apical addition of the A(3) receptor-selective agonist, 2-chloro-N(6)-(3-iodobenzyl)-adenosine-5'-methyluronamide (Cl-IB-MECA) stimulated a chloride secretion that was mediated by calcium- and cAMP-regulated channels. Moreover, in single cell measurements using the fluorescent dye Fura 2-AM, Cl-IB-MECA caused an increase in Ca(2+) influx. The agonist-induced rise in [Ca(2+)](i) was significantly inhibited by the selective adenosine A(3) receptor antagonists, 2,3-diethyl-4, 5-dipropyl-6-phenylpyridine-3-thiocarboxylate-5-carboxylate (MRS 1523) and 3-ethyl 5-benzyl 2-methyl-6-phenyl-4-phenylethynyl-1, 4-(+/-)-dihydropyridine-3,5-dicarboxylate (MRS 1191) but not by antagonists of either A(1) or A(2) receptors supporting the hypothesis that Cl-IB-MECA increases [Ca(2+)](i) by interacting exclusively with A(3) receptors. Cl-IB-MECA-elicited Ca(2+) entry was not significantly inhibited by pertussis toxin pretreatment while being stimulated by cholera toxin preincubation or by raising cellular cAMP levels with forskolin or rolipram. Preincubation with the protein kinase A inhibitor, H89, blunted the Cl-IB-MECA-elicited [Ca(2+)](i) response. Moreover, Cl-IB-MECA elicited an increase in cAMP production that was inhibited only by an A(3) receptor antagonist. Altogether, these data suggest that in A(6) cells a G(s)/protein kinase A pathway is involved in the A(3) receptor-dependent increase in calcium entry.

Alkaline secretion by frog gastric glands measured with pH microelectrodes in the gland lumen.

1. In the present work we have measured the pH of the secreted fluid within the gland lumen of isolated but intact gastric mucosa of Rana esculenta. Tissues were mounted in a double chamber allowing continuous perfusion of the mucosal and serosal compartment, and the measurements were made with double-barrelled pH glass microelectrodes inserted into the glands from the serosal surface under microscopic inspection. 2. During inhibition of H+ secretion by cimetidine (100 microM) the luminal gland pH (pHgl) averaged 7.60 +/- 0.05 pH units (mean +/- s.e.m.; n = 35), a value significantly higher than bath solution pH (7.45 +/- 0.02; P < 0.001) and also higher than intracellular pH of oxyntopeptic cells (pHi), which averaged 7.53 +/- 0.06 (n = 18). 3. Stimulation of acid secretion with histamine (500 microM) reversibly decreased pHgl to values which could be as low as 2.5. Together with electrophysiological criteria this response was routinely used to verify the proper location of the microelectrode tip within the gland lumen. 4. Stimulation with carbachol (100 microM) or pentagastrin (50 microM) in the presence of cimetidine rapidly and reversibly increased pHgl by 0.10 +/- 0.01 pH units (n = 24; P < 0.001) and 0.09 +/- 0.02 pH units (n = 6; P < 0.05), respectively. 5. The observation that gastric gland fluid is more alkaline than the bath solutions and that carbachol or pentagastrin further alkalinize it strongly suggests that oxyntopeptic cells participate in gastric alkaline secretion at least under cholinergic stimulation.

Ca2+ homeostasis in the agonist-sensitive internal store: functional interactions between mitochondria and the ER measured In situ in intact cells.

Mitochondria have a well-established capacity to detect cytoplasmic Ca2+ signals resulting from the discharge of ER Ca2+ stores. Conversely, both the buffering of released Ca2+ and ATP production by mitochondria are predicted to influence ER Ca2+ handling, but this complex exchange has been difficult to assess in situ using conventional measurement techniques. Here we have examined this interaction in single intact BHK-21 cells by monitoring intraluminal ER [Ca2+] directly using trapped fluorescent low-affinity Ca2+ indicators. Treatment with mitochondrial inhibitors (FCCP, antimycin A, oligomycin, and rotenone) dramatically prolonged the refilling of stores after release with bradykinin. This effect was largely due to inhibition of Ca2+ entry pathways at the plasma membrane, but a significant component appears to arise from reduction of SERCA-mediated Ca2+ uptake, possibly as a consequence of ATP depletions in a localized subcellular domain. The rate of bradykinin-induced Ca2+ release was reduced to 51% of control by FCCP. This effect was largely overcome by loading cells with BAPTA-AM, highlighting the importance of mitochondrial Ca2+ buffering in shaping the release kinetics. However, mitochondria-specific ATP production was also a significant determinant of the release dynamic. Our data emphasize the localized nature of the interaction between these organelles, and show that competent mitochondria are essential for generating explosive Ca2+ signals.

Free [Ca2+] dynamics measured in agonist-sensitive stores of single living intact cells: a new look at the refilling process.

Free [Ca2+] in agonist-sensitive internal stores of single intact cells was measured in situ in order to examine the role of [Ca2+] in modulating the store refilling process. BHK-21 fibroblasts were loaded with the low-affinity fluorescent calcium indicator mag-fura-2-AM such that >80% of the dye was trapped in organelles, where it reported [Ca2+] changes solely in an agonist- and thapsigargin-sensitive internal store. The rates of store reloading following stimulation by 100 nM bradykinin were essentially unchanged when cytosolic [Ca2+] was clamped to resting values with BAPTA-AM. In control cells, recharging of stores totally depended on the presence of external Ca2+, but pre-loading the cells with BAPTA-AM permitted efficient refilling in Ca2+-free, EGTA-containing external medium. Our results show: (i) Ca2+ stores normally are recharged by Ca2+ which must first transit the cytoplasm; (ii) an elevation in cytoplasmic [Ca2+] is not required to replenish Ca2+ stores; (iii) the activation of the plasma membrane Ca2+ pump during the Ca2+ spike ordinarily results in complete extrusion of released Ca2+; and (iv) the buffering capacity of the cytoplasm is an essential component of the store refilling process. An interesting finding was that acute treatment of cells with BAPTA-AM activated capacitative Ca2+ entry at the plasma membrane, due to its efficient hydrolysis in the stores, and the ensuing decrease in the endoplasmic reticulum [Ca2+].

Is resting state HCO3- secretion in frog gastric fundus mucosa mediated by apical Cl(-)-HCO3- exchange?

1. We have tested the widely accepted hypothesis that resting-state bicarbonate secretion of gastric fundus mucosa is mediated by Cl(-)-HCO3- exchange in the apical membrane of surface epithelial cells (SECs). To this end, SECs of isolated fundus mucosa of Rana esculenta were punctured with double-barrelled microelectrodes to measure intracellular pH (pHi). 2. No significant pHi changes were observed in response to changing luminal HCO3- and/or Cl- concentrations. The change in pHi (delta pHi) in response to luminal chloride substitution averaged 0.00 +/- 0.01 pH units (mean +/- S.E.M.; n = 48), and did not change after blocking putative basolateral acid/base transporters which could have masked the pHi response. 3. On the other hand, pHi responded readily and reversibly to luminal perfusion with either low-pH (pH 2.5) solution (delta pHi = -0.36 +/- 0.05; n = 4; P < 0.01) or CO2-free HCO3- Ringer solution (delta pHi = +0.10 +/- 0.01; n = 29; P < 0.001). These observations demonstrate that the solution change was effective and complete within 1 min and show that the apical membrane of SECs is permeable to CO2. 4. The apical membrane of frog SECs could not be stained with an antibody against the C-terminal end of the mouse Cl(-)-HCO3- exchanger isoform AE2, although this antibody readily stained the basolateral membrane of the oxyntopeptic cells (OCs). 5. In conclusion, the presence of a Cl(-)-HCO3- exchanger in the apical membrane of SECs of frog gastric fundus mucosa in the resting state could not be confirmed, but other models of HCO3- secretion cannot be fully excluded. Observations from electrical measurements, favouring a model of conductive HCO3- secretion, point to the OCs rather than the SECs as a site of origin of HCO3- secretion.

Model of bicarbonate secretion by resting frog stomach fundus mucosa. I. Transepithelial measurements.

In the present in vitro experiments on gastric fundus mucosa of Rana esculenta we try to define the mechanism of alkaline secretion that is observed in summer frogs in the resting stomach (blockage of HCl secretion by ranitidine, 10(-5) mol/l). The transepithelial voltage and the rate of alkalinization (ASR) of an unbuffered gastric lumen perfusate was measured as a function of serosal (and mucosal) fluid composition. ASR was high (0.88 +/- S.E. 0.09 microEq.cm-2.h-1, n = 11) during serosal bath perfusion with HCO(3-)-Ringer solution, decreased slightly to 0.50 +/- 0.07 microEq.cm-2.h-1 (n = 6) in HCO(3-)-free HEPES-buffered Ringer solution of the same pH, and decreased to approximately 20% when carbonic anhydrase was inhibited by acetazolamide. While replacement of mucosal or serosal Cl- did not--within 1 h--significantly alter ASR, replacement of serosal Na+ in the presence or absence of HCO3- strongly reduced ASR, and a similar reduction was observed after serosal application of the anion transport inhibitor DIDS (4,4-diisothiocyanatostilbene-2,2-disulphonate, 2.10(-4) mol/l), the metabolic poison rotenone (10(-5) mol/l), the uncoupler dinitrophenol (10(-4) mol/l), and the Na+ pump inhibitor ouabain (10(-4) mol/l), while serosal amiloride (10(-4) mol/l) had no effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Model of bicarbonate secretion by resting frog stomach fundus mucosa. II. Role of the oxyntopeptic cells.

In the present publication we report mainly electrophysiological studies on oxyntopeptic cells of frog gastric mucosa which aim at clarifying a possible involvement of these cells in the process of resting gastric alkali (HCO3-) secretion, described in the preceding publication. The experiments were performed on intact gastric fundus mucosa of Rana esculenta mounted in Ussing chambers. After removal of the muscle and connective tissue layer oxyntopeptic cells were punctured from the serosal surface with conventional or pH-sensitive microelectrodes to measure, besides transepithelial voltage and resistance, the basolateral cell membrane potential, the voltage divider ratio, and the cell pH in response to secretagogues and/or changes in serosal ion concentration. Carbachol (10(-4) mol/l), which transiently stimulated HCO3- secretion by 0.22 mumol.cm-2.h-1, transiently acidified the cells by 0.09 +/- SEM 0.03 pH units (n = 6) and transiently induced an apical cell membrane anion conductance. According to the model of gastric HCO3- secretion presented in the preceding publication, this anion conductance could be involved in gastric HCO3- secretion, mediating, besides Cl- efflux, also apical HCO3- efflux. In addition carbachol stimulated basolateral Na+(HCO3-)n-cotransport, which according to the results from the preceding publication mediates basolateral HCO3- uptake for secretion. By contrast, cAMP-mediated secretagogues, such as histamine or others, which stimulate HCl secretion and transiently alkalinize the oxyntopeptic cells, were found to down-regulate the basolateral Na+(HCO3-)n-cotransporter.(ABSTRACT TRUNCATED AT 250 WORDS)

Microelectrode determination of oxyntic cell pH in intact frog gastric mucosa. Effect of histamine.

Intracellular pH (pHi) of acid-secreting cells was measured in intact gastric fundus mucosa of Rana esculenta with double-barrelled pH microelectrodes. Tissues were mounted, serosal side up, between two half chambers and individual cells were impaled after microsurgical removal of the serosal muscle layer. Transepithelial potential difference (Vt) and resistance (Rt) as well as serosal cell membrane potential (Vs) and pHi were continuously recorded at rest (0.1 mmol/l cimetidine) or during stimulation (0.5 mmol/l histamine). During chamber perfusion with HCO3-/CO2-buffered Ringer solution of pHo = 7.36, Vt and Rt were -21.7, SD +/- 6.0 mV and 229 +/- 83 omega cm2 (n = 17) while Vs and pHi averaged -57.3 +/- 6.9 mV and 7.4 +/- 0.11 (n = 25). The latter value is considerably more alkaline than all recent pHi measurements obtained with microspectrofluorometric techniques on isolated cells, glands or intact tissue. The difference may in part be explained by use of HCO3(-)-free solutions in most of the previous studies because we observed that such solutions decrease pHi to 6.89 +/- 0.18 (n = 4). Again, in contrast to recent literature, application of histamine in HCO3-/CO2-buffered solution led to further transient alkalinization by 0.12 +/- 0.05 pH unit (n = 8). Since in accidental punctures of the gastric gland lumen we noticed that H+ secretion only began approximately 5 min after histamine application, we conclude that the histamine-induced initial alkalinization does not reflect stimulation of the H+/K+ ATPase pump.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of histamine on the basolateral K+ conductance of frog stomach oxyntic cells and surface epithelial cells.

The transepithelial potential difference (Vt) and resistance (Rt) and the basolateral cell membrane potential (Vs) of oxyntic cells (OC) and surface epithelial cells (SEC) were measured in isolated stomachs of Rana esculenta. At rest, Vs of OC and SEC was virtually identical [-66.3 +/- 4.5 (SD) (n = 10) and -67.3 +/- 5.9 mV (n = 9)] and both cells responded to increasing serosal K+ concentration from 4 to 13 mmol/l with virtually the same depolarization (delta Vs,K) of +16.2 +/- 2.0 and +16.0 +/- 2.9 mV, respectively, while Vt declined by approximately half as much. Histamine (0.1 mmol/l) reduced Vt and Rt and increased the voltage divider ratio in both cell types, indicating a fall in basolateral membrane resistance. In the OC, this increase was neither associated with a significant alteration of Vs nor with a change in delta Vs,K. In the SEC, however, histamine markedly increased Vs to -75.5 +/- 7.3 mV (n = 9) as well as delta Vs,K to +18.5 +/- 2.6 mV, which was paralleled by an increase in delta Vt,K from 9.8 +/- 3.9 to +12.8 +/- 4.2 mV. The data indicate that 1) both OC and SEC respond to histamine, 2) both OC and SEC contain a basolateral K+ conductance that increases under histamine (in OC probably, in parallel with other ion conductances), and 3) in Rana esculenta the SEC contribute substantially to Vt.

Comparison of the basolateral K+ conductance of the epithelial cells in frog gastric fundus mucosa.

Frog stomach transepithelial potential difference (Vt) and resistance (Rt) as well as the voltage divider ratio (VDR) and serosal membrane potential (VS) of surface epithelial (SEC) and oxyntic (OC) cells were recorded at rest and during stimulation with histamine. Serosal membrane K+ permeability was tested by sudden elevation of serosal K+ concentration from 4 to 13 mmol l-1. Stimulation decreased both Vt and Rt and increased VDR of the OC (from 9.4 +/- SD 3.0 to 14.4 +/- 4.1, n = 10, P less than 0.001), while VS remained virtually unchanged (-66.3 +/- 4.5 mV, n = 10); in SEC, however, VDR as well as VS increased, the latter from -67.3 +/- 5.9 to -75.7 +/- 7.3 mV, n = 9, P less than 0.001. Elevation of serosal K+ reversibly diminished Vt and Vs in both cell types. The transepithelial response to K+ increased after stimulation. However, the cell potential response delta Vs,K increased only in the SEC (from +16.0 +/- 2.9 to +18.5 +/- 2.6 mV, n = 9, P less than 0.001) but not significantly in the OC. We conclude that in frog stomach both OC and SEC are stimulated by histamine: the SEC respond with a hyperpolarization, which reflects an increase in their basolateral K+ conductance; the OC do not respond with a hyperpolarization, possibly because histamine increases the basolateral membrane K+ conductance as well as other ion conductances which have not yet been identified.

Evidence for rheogenic sodium bicarbonate cotransport in the basolateral membrane of oxyntic cells of frog gastric fundus.

Ionic conductance properties of the basolateral cell membrane of oxyntic cells were studied in frog gastric fundus in vitro. After mounting the fundus in a modified Ussing chamber the serosal connective tissue was dissected off and individual oxyntic cells were punctured from the serosal surface with microelectrodes. Under resting conditions the membrane potential averaged -56.9, SD +/- 9.5 mV (n = 63), cytoplasm negative. Lowering or raising serosal HCO-3 concentration from 17.8 to 6 or 36 mmol/l respectively at constant PCO2 depolarized or hyperpolarized the cell membrane by +16.7 or -18.2 mV respectively. Sudden removal of serosal Na+ also depolarized the cell membrane (anomalous Nernst response). Since both the HCO-3 dependent and the Na+ dependent potential changes were strongly depressed by the disulfonic stilbene SITS and since the potential response to HCO-3 was virtually abolished in Na+-free solution we conclude that a rheogenic Na+ (HCO-3)n-cotransport system (n greater than 1) is present in the basolateral cell membrane of oxyntic cells. Its possible role in base transfer during HCl-secretion or HCO-3 secretion remains to be elucidated.

A transitional anterior fixed prosthesis using composite resin.

A method has been described to temporarily restore an anterior edentulous space in a single appointment. The technique uses a composite resin to retain a resin denture tooth (pontic) supported by edgewise orthodontic wire. This approach is suggested as a transitional treatment for patients who are not amenable to either a definitive fixed or removable prosthesis.