Fall In pH Research Articles

A nocturnal decline of salivary pH associated with airway hyperresponsiveness in asthma

Salivary pH is associated with esophageal acid reflux and neutralization of esophageal acid. In this study, we assessed the association between nocturnal decline of salivary pH and airway hyperresponsiveness. Salivary pH was serially assessed in 9 patients with mild asthma (7 men and 2 women; mean age 33.3 years; mean %predicted FEV(1.0) 89.4%) and 10 healthy volunteers (6 men and 4 women; mean age 31.2 years) using a pH indicator tape. The buffering capacity of saliva was defined as the median effective dose (ED(50)) for acidification of saliva with 0.01 N HCl, and airway responsiveness was defined as the dose of methacholine producing a 35% fall in Grs (PD(35)-Grs). There was a significant correlation between the values obtained from the pH indicator tape and those obtained from the electrometric pH meter. Using the indicator tape for sequential monitoring, we observed a nocturnal fall (ΔpH) in salivary pH in all subjects. A significant correlation was found between airway hyperresponsiveness (PD(35)-Grs) and either ΔpH or ED(50) in mildly asthmatic patients. Vagal reflux dysfunction might contribute to nocturnal salivary pH as well as to airway hyperresponsiveness in mild asthmatics.

Quality of lamb meat from the Information Nucleus Flock

The effects of production and processing factors on tenderness, and colour of lamb meat produced from 7 locations as part of the Australian Sheep Industry CRC’s Information Nucleus flock were investigated, using data from 2052 lambs slaughtered in 2007. At 24 h post-slaughter, samples of m. longissimus lumborum (LL) and m. semimembranosus (SM) were collected for measurement of intramuscular fat (IMF), myoglobin, iron and copper and fresh meat colour (L*, a*, b*) and pH at 24 h measured on the LL. pH and temperature measurements made pre-rigor were used to calculate the pH at 18°C. Tenderness was measured by LL shear force at days 1 (SF1) and 5 (SF5) post-slaughter, the shear force difference (SF-diff) and SM compression and collagen concentration were determined. Retail colour stability was assessed using over-wrapped LL under simulated retail display for 3 days, according to the change in the oxymyoglobin/metmyoglobin ratio. All traits were affected by flock and date of slaughter (P < 0.001). After 4 days of ageing, 70–95% of the LL samples from all flocks, except for one, had acceptable tenderness for consumers based on their shear force. Low IMF, high LL pH at 18°C and high pH at 24 h increased SF1 and SF5 and also had an effect on SF-diff (P < 0.001). The retail colour of 44.8% of the samples on day 3 of retail display were lower than acceptable. Retail colour was influenced by IMF, pH18 and the concentration of iron and copper (P < 0.001). In conclusion, breeding and management practices that increase muscle IMF levels and reduce ultimate pH values and processing practices that result in moderate rates of pH fall post-slaughter, improve the tenderness of lamb. Extension of retail colour stability may be antagonistic to traits associated with tenderness and nutritional traits, particularly IMF and mineral levels.

The effects of stunning methods on product qualities in force-fed ducks and geese. 1. Carcass downgrading and meat quality

This study investigated the effects of various stunning methods on the quality of carcass and meat in ducks and geese force-fed for the production of French ‘foie gras’. The ducks (n = 30 per group) were stunned with one of the following techniques: electrical stunning in a water bath (50 Hz AC, 130 mA, 4 s), head-only electrical stunning (50 Hz AC, 600 mA, 4 s), mechanical stunning (captive bolt) and controlled atmosphere stunning (CAS: phase 1, CO2 (40%)–O2 (30%)–N2 (30%), for 2 min followed by phase 2, CO2 > 85% in air, for 2 min). The same methods (except head-only stunning which was not applied) were used in geese (n = 40 per group). During the first 5 min after slaughter, the stunning techniques that did not kill the animals were associated with a high incidence of head movements (mechanical and electrical head-only stunning), convulsions and convulsive wing flapping (mechanical stunning), in both species. Consequently, the rate of post-mortem pH fall in breast muscle was enhanced and the meat was paler when measured at 24 h or 6 days post mortem (L*, a*, b* coordinates). In ducks, the animals stunned in the water bath showed the lowest bleeding efficiency, compared to the three other procedures. In geese, the mechanical stunning allowed the highest recovery of blood compared to the CAS and the water-bath methods. Meat texture assessed instrumentally and fluid losses during storage and processing were not affected by the stunning method in any species. Sensory analysis showed a higher score for bloody appearance of raw meat in ducks stunned with the methods that kill before neck cutting (water-bath and CAS). This effect was, however, not linked to the rate of bleeding. The sensory properties of cooked meat were not affected by the stunning method. In both ducks and geese, CAS was associated with the lowest rate of fractures of humeral bone but CAS-stunned geese showed the most engorged wing veins. Overall, these results show the positive effect of CAS on the appearance defects of carcass and meat of ducks and geese, and, on the contrary, they confirm the detrimental effects of water-bath stunning on these criteria. However, the incidences on meat sensory qualities were scarce.

Meat production traits of a new sheep breed called Bafra in Turkey 2. Meat quality characteristics of lambs

Meat quality characteristics of Bafra ram lambs slaughtered at different weights were investigated. A total of 24 lambs fattened intensively was slaughtered at four slaughter weights of 30, 35, 40, and 45 kg. Water-holding capacity, cooking loss, tenderness, color, as well as protein content did not vary significantly among the slaughter weight groups, although the 30-kg slaughter weight lambs displayed the greatest postmortem pH fall in musculus longissimus dorsi (P < 0.05). As slaughter weight increased, intramuscular fat of musculus longissimus dorsi showed an increasing nutritive value (P < 0.05), total unsaturated fatty acids/saturated fatty acids ratio (P < 0.05), and n6/n3 ratio (P < 0.05). However, atherogenic index and thrombogenic index values decreased with increasing slaughter weight, although this effect was not significant. The effect of slaughter weight on total cholesterol was not pronounced.

Cytoplasmic Histidine Kinase (HP0244)-Regulated Assembly of Urease with UreI, a Channel for Urea and Its Metabolites, CO 2 , NH 3 , and NH 4 + , Is Necessary for Acid Survival of Helicobacter pylori

Helicobacter pylori colonizes the normal human stomach by maintaining both periplasmic and cytoplasmic pH close to neutral in the presence of gastric acidity. Urease activity, urea flux through the pH-gated urea channel, UreI, and periplasmic alpha-carbonic anhydrase are essential for colonization. Exposure to pH 4.5 for up to 180 min activates total bacterial urease threefold. Within 30 min at pH 4.5, the urease structural subunits, UreA and UreB, and the Ni(2+) insertion protein, UreE, are recruited to UreI at the inner membrane. Formation of this complex and urease activation depend on expression of the cytoplasmic sensor histidine kinase, HP0244. Its deletion abolishes urease activation and assembly, impairs cytoplasmic and periplasmic pH homeostasis, and depolarizes the cells, with an approximately 7-log loss of survival at pH 2.5, even in 10 mM urea. Associated with this assembly, UreI is able to transport NH(3), NH(4)(+), and CO(2), as shown by changes in cytoplasmic pH following exposure to NH(4)Cl or CO(2). To be able to colonize cells in the presence of the highly variable pH of the stomach, the organism expresses two pH-sensor histidine kinases, one, HP0165, responding to a moderate fall in periplasmic pH and the other, HP0244, responding to cytoplasmic acidification at a more acidic medium pH. Assembly of a pH-regulatory complex of active urease with UreI provides an advantage for periplasmic buffering.

β-Alanine supplementation reduces acidosis but not oxygen uptake response during high-intensity cycling exercise

The oral ingestion of beta-alanine, the rate-limiting precursor in carnosine synthesis, has been shown to elevate the muscle carnosine content. Carnosine is thought to act as a physiologically relevant pH buffer during exercise but direct evidence is lacking. Acidosis has been hypothesised to influence oxygen uptake kinetics during high-intensity exercise. The present study aimed to investigate whether oral beta-alanine supplementation could reduce acidosis during high-intensity cycling and thereby affect oxygen uptake kinetics. 14 male physical education students participated in this placebo-controlled, double-blind study. Subjects were supplemented orally for 4 weeks with 4.8 g/day placebo or beta-alanine. Before and after supplementation, subjects performed a 6-min cycling exercise bout at an intensity of 50% of the difference between ventilatory threshold (VT) and VO(2peak). Capillary blood samples were taken for determination of pH, lactate, bicarbonate and base excess, and pulmonary oxygen uptake kinetics were determined with a bi-exponential model fitted to the averaged breath-by-breath data of three repetitions. Exercise-induced acidosis was significantly reduced following beta-alanine supplementation compared to placebo, without affecting blood lactate and bicarbonate concentrations. The time delay of the fast component (Td(1)) of the oxygen uptake kinetics was significantly reduced following beta-alanine supplementation compared to placebo, although this did not reduce oxygen deficit. The parameters of the slow component did not differ between groups. These results indicate that chronic beta-alanine supplementation, which presumably increased muscle carnosine content, can attenuate the fall in blood pH during high-intensity exercise. This may contribute to the ergogenic effect of the supplement found in some exercise modes.

Rapid effects of hypoxia on H+ homeostasis in articular chondrocytes

Articular chondrocytes experience low oxygen (O(2)) levels compared with many other tissues, and values fall further in disease states. Chondrocyte intracellular pH (pH(i)) is a powerful modulator of matrix synthesis and is principally regulated by Na(+)-H(+) exchange (NHE). In equine chondrocytes, NHE is inhibited when cells are incubated for 3 h at low O(2), leading to intracellular acidosis. O(2)-dependent changes in reactive oxygen species (ROS) levels appear to underlie this effect. The present study examines whether hypoxia can influence chondrocyte NHE activity and pH(i) over shorter timescales using the pH-sensitive fluoroprobe BCECF in cells isolated not only from equine cartilage but also from bovine tissue. O(2) levels in initially oxygenated solutions gassed with N(2) fell to approximately 1% within 2 h. A progressive fall in pH(i) and acid extrusion capacity was observed, with statistically significant effects (P < 0.05) apparent within 3 h. For equine and bovine cell populations subjected to step change in O(2) by resuspension in hypoxic (1%) solutions, a decline in acid extrusion and pH(i) was observed within 10 min and continued throughout the recording period. This effect represented inhibition of the NHE-mediated fraction of acid extrusion. Cells subjected to hypoxic solutions supplemented with CoCl(2) (100 microM) or antimycin A (100 microM) to raise levels of ROS did not acidify. The conserved nature and rapidity of the response to hypoxia has considerable implications for chondrocyte homeostasis and potentially for the maintenance of cartilage integrity.

Effects of transportation during the hot season and low voltage electrical stimulation on histochemical and meat quality characteristics of sheep longissimus muscle

The effect of transportation during the hot season (42 °C) and low voltage electrical stimulation on physiological, histochemical and meat quality characteristics of Omani sheep was studied. Forty intact male sheep were divided into two equal groups: 3 h transported or non-transported. The non-transported group remained in holding pens for 48 h prior to slaughter, while the transported group was transported 300 km (approximately 3 h) in an open truck under solar radiation on the day of slaughter. Blood samples were collected from the animals before loading and prior to slaughter. Fifty percent of the carcasses from each group were randomly assigned to low voltage (90 V) at 20 min postmortem. Temperature and pH decline of the left longissimus thoracis muscle were monitored. Ultimate pH, WB-shear force, sarcomere length, myofibrillar fragmentation index (MFI), expressed juice, cooking loss and color L⁎, a⁎, b⁎ were measured on samples from both sides muscles collected at 24 h postmortem at 3–4 °C. The transported sheep had significantly higher plasma cortisol ( P < 0.01), adrenaline, nor-adrenaline and dopamine concentrations ( P < 0.05) than non-stimulated animals. Electrical stimulation resulted in a significantly ( P < 0.05) more rapid pH fall in muscle during the first 12 h after slaughter. Muscles from electrically-stimulated carcasses had significantly ( P < 0.05) lower pH values, longer sarcomere length, lower shear force value, higher expressed juice, MFI and lighter L⁎ than those from non-stimulated ones. The muscle samples from the transported sheep had significantly ( P < 0.05) smaller and lower proportion of Types I and IIA fibers than those from the non-transported group. This study indicated that pre-slaughter transport at high ambient temperatures can cause noticeable changes in physiological and muscle metabolism responses in sheep. Electrical stimulation improved meat quality characteristics, which indicate that meat quality of transported sheep can be improved by electrical stimulation.

The anomalous effect of high intensity ultrasound on paper fibre‐filler combinations

PurposeThe purpose of this paper is to explore the previously unreported phenomenon in which changes occur to the particle size distributions of calcium carbonate fillers, used in papermaking, when exposed to high intensity ultrasound.Design/methodology/approachCommercial paper pulps sonicated at a frequency of 20 kHz are found to produce aggregates of their mineral filler constituents. The effects of sonication on isolated long and short fibre, and ground and precipitated calcium carbonate filler systems are also investigated both with and without the presence of dispersants. The findings are supported by particle size analysis and scanning electron microscopy of the sonicated systems.FindingsIt is clearly shown that exposure to high intensity ultrasound induces filler aggregation. However, the effect only occurs when paper fibres and fillers coexist and is not apparent for suspensions of filler only or fibre only slurries. Furthermore, the treatment overrides the effect of dispersants used to keep filler in suspension during the manufacturing process. An accompanying fall in pH with increasing sonication times is also noted and is linked to these changes. It is proposed that radical species produced in the slurries during sonication may explain the observed phenomenon.Research limitations/implicationsThe role of pH is not clearly understood and needs further study.Practical implicationsThe findings may be of interest in paper manufacture where uniform dispersal of fillers throughout the pulp is of significant importance.Originality/valueThe phenomenon described in this paper has not previously been reported or explored. Further studies may add to knowledge of filler dispersions and their behaviour in papermaking.

Potential impact of metabolic acidosis on the fixed-acid Bohr effect in snapper ( Pagrus auratus) following angling stress

Oxygen equilibrium data were obtained for intact erythrocytes from Pagrus auratus and the pH-dependence of the fixed-acid Bohr and Root effects described. Indicators of aerobic–anaerobic poise were then measured following a period of strenuous exercise induced by angling capture. Haematological indices and plasma metabolites were evaluated with respect to their potential impact on the blood oxygen transport mechanism. An increase in post-capture haemoglobin content, blood lactate, and glucose were observed. The fall in caudal venous pH from 7.53 to 7.41, reflecting the acid–base status of blood draining the working tail musculature, remained within the operational zone of the maximal fixed-acid Bohr effect ( Φ 7.4–7.8 = − 0.95), but above the critical pH at which the Root effect suppresses oxygen transport capacity. These stress-induced changes reflect a strategy of optimal O 2 unloading to tissues with the Root effect unlikely to be expressed in the swimming vasculature.

The effect of casein and calcium containing paste on plaque pH following a subsequent carbohydrate challenge

Objectives Previous research has shown that regular use of CPP–ACP increases calcium and inorganic phosphates in plaque and reduces enamel mineral loss. The aim of this study was to investigate if a CPP–ACP-containing paste would neutralize acidic challenges in dental plaque following sucrose rinse. Method Plaque pH was measured on 15 subjects in a cross-over study with and without prior application of the paste and with and without CPP–ACP. On each occasion, subjects rinsed with 10% sucrose and sorbitol solutions for 2 min in randomized order. Results The results showed the median lowest pH without paste was 4.8 (IQR: 4.7–5.0) and with mousse 5.6 (IQR: 5.5–5.6 and p < 0.001). The median lowest pH was 5.0 (IQR: 4.9–5.3) without CPP–ACP and with CPP–ACP was 5.8 (5.6–6.1 and p < 0.001). The time that pH remained below 5.7 and the time to return to resting pH showed similar differences in all subjects ( p < 0.01). Conclusion The results indicate that prior application of a CPP–ACP-containing paste reduced the fall in plaque pH following a sucrose challenge.

Current theories on the pathophysiology of equine laminitis – the link between the gut and foot

Equine laminitis is a painful debilitating condition that seems to be a product of domestication of horses associated with the practice of feeding carbohydrate rich pasture in excess of requirements, particularly in ponies. We have been working on the hypothesis that caecal bacteria, when presented with carbohydrate in large quantities tend to ferment this. Fermentation by gram positive bacteria is associated with a fall in pH of the caecal liquor. As a means of providing themselves with increased intracellular buffering capacity, these bacteria produce amino acid decarboxylase enzymes which convert amino acids present in the caecal fluid into primary amines which can act as intracellular buffers. The reason we thought this might be the case was that foods formed by bacterial fermentation processes (e.g. cheese and wines) have a high content of amines. Primary amines derived from some amino acids have vasoactive properties. In the 1960s it was recognised that human patients taking drugs that inhibit the metabolism of amines (monoamine oxidase inhibitors) could suffer from severe hypertensive crises if they ate cheese or drank red wines with high tyramine content. This so called ‘cheese effect’ is the result of the indirect sympathomimetic effect of tyramine which displaces norepinephrine from sympathetic nerve endings leading to a rise in blood pressure. Monoamine oxidase enzymes present in the epithelial cells lining the gut wall and in liver cells normally protect individuals from suffering these hypertensive crises. We wondered whether amines released from the gut in response to ingestion of excessive amounts of carbohydrate might lead to a similar reaction in ponies whereby dietary amines caused vasoconstriction of the digital vasculature, leading to the prodromal phases of laminitis.

Blockade of Na+/H+ exchange enhances phrenic burst frequency under control conditions but not in response to hypercapnia in arterially‐perfused adult rat

Increased levels of CO2 (hypercapnic acidosis, HA) produce a marked increase in ventilation. Numerous studies have suggested that this hypercapnia‐induced respiratory excitation results from the fall in intracellular pH (pHi), and that Na+/H+ exchange (NHE) plays an important role in regulating pHi recovery during HA. In CO2 chemosensitive respiratory neurons, however, pHi recovery is not observed during HA. The current study was therefore undertaken to determine the role of NHE in respiratory activity under control conditions and in response to HA. To address this issue, we examined phrenic nerve discharge in response to increasing CO2 from 5% to 10% in an arterially‐perfused adult rat preparation (n=5) under control conditions and during NHE blockade using dimethyl‐amiloride hydrochloride (DMA, 283 µM). Under control conditions, HA increased burst frequency by ~34% (P&lt;0.01) due to a marked reduction in TE (~25%, P&lt;0.01) and a small decrease in TI (~15%, P=0.1). Perfusion with DMA elicited a robust increase in burst frequency of ~65% (P&lt;0.001) due solely to a reduction in TE (P&lt;0.001). Under these conditions, burst frequency was not further altered by HA (P=0.2) although TI was still decreased by ~15% (P&lt;0.05). These results indicate that interference with pHi regulation is capable of enhancing phrenic burst frequency under control conditions but is ineffective in altering burst frequency during HA. Supported by NS045321

Telmisartan, an Angiotensin II receptor blocker, abrogates troglitazone‐induced cell signaling coupled to ammoniagenesis in proximal tubule‐like LLC‐PK1 cells

Troglitazone(TRO) induces a large increase in ammonium production from glutamine via the mitochondrial pathway in proximal tubule‐like LLC‐PK1 cells. To elucidate the upstream site of tro action we measured the acute effects on cell signaling in LLC‐PK1 cells grown in chambers designed for fluorometric ratiometric imagining (BCECF and Fura 2) and in 24 well plates for 18h metabolic studies. TRO (25uM) induces a large fall (p&lt;0.01) in cytosolic pH (7.19±0.09 to 6.85±0.08) and a doubling of cell calcium occurring within 8minutes. Associated with these responses was a similarly rapid and large increase (p&lt;0.05) in phospho‐ERK1/2(p‐ERK to total ERK ratio=1±0.2 for control vs 10.1±3 fold for TRO). Treating the cells with 30uM telmisartan (pre‐incubation for 4minutes and during 8minutes with TRO) markedly reduced both the rise in p‐ERK1/2(10.1±3 to 2.4±0.5) and acidity (6.85±0.08 to 7.11± 0.07) suggesting that telmisartan acutely blocks TRO's upstream site of action. At the downstream site, TRO (25uM) enhanced (p&lt;0.01) mitochondrial ammoniagenesis (NH4+ production 1011±110 to 1678±84nmol/mg/18h) despite a normal extracellular bicarbonate concentration and pH; addition of telmisartan (30uM) to the TRO‐media prevented (p&lt;0.05) the enhanced ammonium production (1193±142 vs 1678±84 nmol/mg/18h for TRO+telmisartan vs TRO). These findings are consonant with angiotensin II‐like receptor involvement in TRO's initial activation of cell signaling pathways underlying the ammoniagenic response in these model porcine proximal tubule‐like cells.

A Ca(2+)-calmodulin-eEF2K-eEF2 signalling cascade, but not AMPK, contributes to the suppression of skeletal muscle protein synthesis during contractions.

Skeletal muscle protein synthesis rate decreases during contractions but the underlying regulatory mechanisms are poorly understood. It was hypothesized that there would be a coordinated regulation of eukaryotic elongation factor 2 (eEF2) and eukaryotic initiation factor 4E-binding protein 1 (4EBP1) phosphorylation by signalling cascades downstream of rises in intracellular [Ca(2+)] and decreased energy charge via AMP-activated protein kinase (AMPK) in contracting skeletal muscle. When fast-twitch skeletal muscles were contracted ex vivo using different protocols, the suppression of protein synthesis correlated more closely with changes in eEF2 than 4EBP1 phosphorylation. Using a combination of Ca(2+) release agents and ATPase inhibitors it was shown that the 60-70% suppression of fast-twitch skeletal muscle protein synthesis during contraction was equally distributed between Ca(2+) and energy turnover-related mechanisms. Furthermore, eEF2 kinase (eEF2K) inhibition completely blunted increases in eEF2 phosphorylation and partially blunted (i.e. 30-40%) the suppression of protein synthesis during contractions. The 3- to 5-fold increase in skeletal muscle eEF2 phosphorylation during contractions in situ was rapid and sustained and restricted to working muscle. The increase in eEF2 phosphorylation and eEF2K activation were downstream of Ca(2+)-calmodulin (CaM) but not other putative activating factors such as a fall in intracellular pH or phosphorylation by protein kinases. Furthermore, blunted protein synthesis and 4EBP1 dephosphorylation were unrelated to AMPK activity during contractions, which was exemplified by normal blunting of protein synthesis during contractions in muscles overexpressing kinase-dead AMPK. In summary, in fast-twitch skeletal muscle, the inhibition of eEF2 activity by phosphorylation downstream of Ca(2+)-CaM-eEF2K signalling partially contributes to the suppression of protein synthesis during exercise/contractions.

Concentration-Dependent Effects on Intracellular and Surface pH of Exposing Xenopus oocytes to Solutions Containing NH3/NH4 +

Others have shown that exposing oocytes to high levels of NH(3)/NH(4)(+) (10-20 mM) causes a paradoxical fall in intracellular pH (pH(i)), whereas low levels (e.g., 0.5 mM) cause little pH(i) change. Here we monitored pH(i) and extracellular surface pH (pH(S)) while exposing oocytes to 5 or 0.5 mM NH(3)/NH(4)(+). We confirm that 5 mM NH(3)/NH(4)(+) causes a paradoxical pH(i) fall (-DeltapH(i) approximately equal 0.2), but also observe an abrupt pH(S) fall (-DeltapH(S) approximately equal 0.2)-indicative of NH(3) influx-followed by a slow decay. Reducing [NH(3)/NH(4)(+)] to 0.5 mM minimizes pH(i) changes but maintains pH(S) changes at a reduced magnitude. Expressing AmtB (bacterial Rh homologue) exaggerates -DeltapH(S) at both NH(3)/NH(4)(+) levels. During removal of 0.5 or 5 mM NH(3)/NH(4)(+), failure of pH(S) to markedly overshoot bulk extracellular pH implies little NH(3) efflux and, thus, little free cytosolic NH(3)/NH(4)(+). A new analysis of the effects of NH(3) vs. NH(4)(+) fluxes on pH(S) and pH(i) indicates that (a) NH(3) rather than NH(4)(+) fluxes dominate pH(i) and pH(S) changes and (b) oocytes dispose of most incoming NH(3). NMR studies of oocytes exposed to (15)N-labeled NH(3)/NH(4)(+) show no significant formation of glutamine but substantial NH(3)/NH(4)(+) accumulation in what is likely an acid intracellular compartment. In conclusion, parallel measurements of pH(i) and pH(S) demonstrate that NH(3) flows across the plasma membrane and provide new insights into how a protein molecule in the plasma membrane-AmtB-enhances the flux of a gas across a biological membrane.

Differentiation impairs low pH-induced Ca 2+ signaling and ERK phosphorylation in granule precursor tumour cells

Extracellular acidification is a hallmark of a number of debilitating pathologies including cancer, ischemia and inflammation. We have recently shown that in human granule precursor tumour cells a fall in extracellular pH triggers increases in intracellular Ca 2+ concentration through activation of G-protein coupled proton-sensing receptors coupling to phospholipase C. This pH-dependent rise in cytosolic Ca 2+ led to activation of the extracellular signal-regulated kinase ERK, providing a mechanistic explanation of how extracellular acidification can promote tumour growth. We now find that differentiation of granule precursor tumour cells profoundly affects their ability to respond to extracellular acidification with gene transcription. Differentiating cells have a lower Ca 2+ release probability from intracellular Ca 2+ stores upon acidification and cells that respond have a significantly smaller and slower Ca 2+ signal than proliferating cells. Importantly, Ca 2+ release in differentiating cells fails to evoke ERK phosphorylation. This altered responsiveness of differentiating cells is not due to reduced proton-sensing receptor expression or diminished Ca 2+ store content. Rather, our results suggest that in differentiating cells, the proton-sensing receptor couples less effectively to phospholipase C activation and IP 3 formation. Hence, the ability of human granule cells to respond to extracellular acidification by generating Ca 2+ signals and ERK activation is state-dependent, being lost upon differentiation.

Fluoride released from glass-ionomer cement is responsible to inhibit the acid production of caries-related oral streptococci

Objectives Glass-ionomer cements (GICs) are known to have inhibitory effects on bacterial growth, but the biochemical mechanism of this property has not been fully understood. This study aimed to evaluate inhibitory effects of GIC on the acid production of caries-related oral streptococci, and to identify the components responsible for the inhibition. Methods An eluate was prepared by immersing set GIC in phosphate-buffered saline at 37 °C for 24 h. Fluoride and other elements in the eluate were quantified by fluoride ion electrode and atomic absorption photometry, respectively. Streptococcus mutans NCTC 10449 and Streptococcus sanguinis NCTC 10556 were used to evaluate the pH fall and the rate of acid production after the addition of glucose in the presence or absence of the eluate. Acidic end products from glucose were also assayed by carboxylic acid analyzer. Results The eluate contained silicon (1.24 ± 0.26 mM), fluoride (0.49 ± 0.02 mM) and aluminum (0.06 ± 0.00 mM), and inhibited the pH fall and the acid production rate of both streptococci at acidic pH, with a concomitant decrease in lactic acid production. These effects were comparable to those of a potassium fluoride solution containing the same concentration of fluoride as the eluate. Significance These results indicate that the GIC eluate inhibits the acid production of caries-related oral streptococci at acidic pH and that the effect is due to fluoride derived from the GIC. Thus, adjacent to GIC fillings, bacterial acid production and the subsequent bacterial growth may decrease, establishing a cariostatic environment.

Effects of α-Amylase and Its Inhibitors on Acid Production from Cooked Starch by Oral Streptococci

This study evaluated acid production from cooked starch by Streptococcus mutans, Streptococcus sobrinus, Streptococcus sanguinis and Streptococcus mitis, and the effects of α-amylase inhibitors (maltotriitol and acarbose) and xylitol on acid production. Streptococcal cell suspensions were anaerobically incubated with various carbohydrates that included cooked potato starch in the presence or absence of α-amylase. Subsequently, the fall in pH and the acid production rate at pH 7.0 were measured. In addition, the effects of adding α-amylase inhibitors and xylitol to the reaction mixture were evaluated. In the absence of α-amylase, both the fall in pH and the acid production rate from cooked starch were small. On the other hand, in the presence of α-amylase, the pH fell to 3.9–4.4 and the acid production rate was 0.61–0.92 μmol per optical density unit per min. These values were comparable to those for maltose. When using cooked starch, the fall in pH by S. sanguinis and S. mitis was similar to that by S. mutans and S. sobrinus. For all streptococci, α-amylase inhibitors caused a decrease in acid production from cooked starch, although xylitol only decreased acid production by S. mutans and S. sobrinus. These results suggest that cooked starch is potentially acidogenic in the presence of α-amylase, which occurs in the oral cavity. In terms of the acidogenic potential of cooked starch, S. sanguinis and S. mitis were comparable to S. mutans and S. sobrinus. α-Amylase inhibitors and xylitol might moderate this activity.

Bacterial Utilization of Petroleum in Liquid and Simulated Soil Environments

Ten bacterial isolates designated S1 to S10 were obtained from hydrocarbon. Polluted soils in Nsukka and studied for their hydrocarbonoclastic potentials. After screening for hydrocarbon utilizing capability, isolates S2 and S8, identified as Bacillus subtilis and Pseudomonas aeruginosa respectively, were selected for the study owing to their impressive utilization of crude oil as sole carbon source. Hydrocarbon utilization in liquid medium as assessed by the parameters of optical density (OD600), surface tension and pH showed engine oil as the worst substrate for the growth of the two isolates. S2 grew best on kerosene (maximum OD600 = 1.56). Optical density increased progressively with a concomitant fall in medium pH and surface tension for the two isolates during the 96h-experiment. A simulated bioremediation study was conducted using soil samples dispensed in 50.0g weights into 250ml conical flasks and contaminated with different levels (2.5%, 5.0%, 7.5% or 10.0%v/w) of Bonny light crude oil. A saturated solution of NPK (15:15:15) compound fertilizer was added at the ratio of crude oil to NPK of 10.0:1.0 and each flask inoculated with 1.0ml of S8 isolate containing 3x108 cells. Microbial utilization of the oil in the soil as assessed by the weight of extracted residual oil indicated that the extents of oil removal in the stimulated and/or bioaugmented soils were significantly high in relation to unsupplemented and uninoculated controls. Keywords: Bacterial utilization, Petroleum in liquid, Petroleum in soil, EnvironmentsBio-Research Vol. 6 (2) 2008: pp. 375-379