pH, EF-1alpha and the cytoskeleton

One of the unexpected cellular components found interacting with the cytoskeleton is elongation factor 1 alpha (EF-1alpha). How this interaction is regulated is not clear, but pH may be a potent regulator. Interestingly, pH also regulates the amount of protein translation occurring in many cell systems. In this paper, the authors suggest that sequestration of EF-1alpha in the cytoskeleton may play a key role in regulating the spatial distribution of macromolecular assembly in a way that is dependent on cytoplasmic pH.     

Effects of Environmental pH on the Internal pH of Chlorella pyrenoidosa, Scenedesmus quadricauda, and Euglena mutabilis

The effect of external pH on two laboratory-cultured acid-intolerant species (Chlorella pyrenoidosa Chick and Scenedesmus quadricauda Turp. Bréb.) and one acid-tolerant species from a natural population (Euglena mutabilis Schmitz) was examined by measuring internal pH. These measurements were made with the weak acid ¹⁴C-dimethyloxazolidine-2,4-dione after cells had been incubated for 2 and 6 hours at external pH levels from 3.0 to 8.0. Photosynthetic and respiration rates of the three species were also measured over the range of external pH levels.     

Relationships between extracellular pH, intracellular pH, and gene expression in Dictyostelium discoideum

A variety of studies have shown that differentiation of Dictyostelium discoideum amoebae in the presence of cAMP is strongly influenced by extracellular pH and various other treatments thought to act by modifying intracellular pH. Thus conditions expected to lower intracellular pH markedly enhance stalk cell formation, while treatments with the opposite effect favor spores. To directly test the idea that intracellular pH is a cell-type-specific messenger in Dictyostelium, we have measured intracellular pH in cells exposed to either low extracellular pH plus weak acid or high extracellular pH plus weak base using 31P nuclear magnetic resonance (NMR). Our results show that there is no significant difference in intracellular pH (cytosolic or mitochondrial) between pH conditions which strongly promote either stalk cell or spore formation, respectively. We have also examined the effects of external pH on the expression of various cell-type-specific markers, particularly mRNAs. Some mRNAs, such as those of the prestalk II (PL1 and 2H6) and prespore II (D19, 2H3) categories, are strongly regulated by external pH in a manner consistent with their cell-type specificity during normal development. Other markers such as mRNAs D14 (prestalk I), D18 (prespore I), 10C3 (common), or the enzyme UDP-galactose polysaccharide transferase are regulated only weakly or not at all by external pH. In sum, our results show that modulation of phenotype by extracellular pH in cell monolayers incubated with cAMP does not precisely mimic the regulation of stalk and spore pathways during normal development and that this phenotypic regulation by extracellular pH does not involve changes in intracellular pH.     

Osmoregulation in Dunaliella tertiolecta: effects of salt stress,and the external pH on the internal pH

The intracellular pH of the halotolerant green algae Dunaliella tertiolecta, was determined by the distribution of 5,5-dimethyl-2(¹⁴C)-oxalolidine-2,5-dione (DMO) between the cell and the surrounding medium. 5,5-dimethyl-2(¹⁴C)oxalolidine-2,4-dione was not metabolized by the algal cells. The intracellular pH of Dunaliella tertiolecta was 6.8 in the dark and 7.4 in the light. During a salt stress, after two hours, the intracellular pH was increased by 0.2 pH units in both light and dark. The salt stressed cells maintained a constant pH of about 7.5 over the pH range of 6.5 to 8.5. Because of the relatively low permeability coefficient of the plasma membrane for DMO, this technique does not permit rapid pH determinations during the induction period after a salt stress. The magnitude of the salt induced pH changes measured 2 h after the salt stress implies a minor importance of this alkalization in this time range, but does not exclude a larger importance of pH changes for osmoregulation during the induction period.Abbreviations Chl chlorophyll - DMO 5,5-dimethyl-2(¹⁴C)oxalolidine-2,4-dione - PCV packed cell volume - SDS sodium dodecyl sulfate     

The Hyperpolarization of the Chara Membrane at High pH: Effects of External Potassium, Internal pH, and DCCD

At high external pH, the Chara membrane is known to switch toa new state in which the membrane potential is highly negative;it has been characterized as a passive diffusion potential forH⁺ (or 0H^–). DCCD is shown to inhibit the increased conductanceand the highly negative membrane potential associated with thisstate. DCCD also inhibits the plasmalemma H⁺-ATPase, as wellas cytoplasmic streaming. The alkaline state of the membraneis shown to involve a decreased permeability to K⁺; this enhancesthe selectivity for H⁺ (or OH^–) which results from theincreased permeability to H⁺ (or OH^–). Altering the cytoplasmicpH affects the membrane potential at both neutral and alkalinepH. It can also affect the ability of the cell to make the transitionto the alkaline state.     

Rhizosphere pH dynamics in trace-metal-contaminated soils, monitored with planar pH optodes

The present study presents new insights into pH dynamics in the rhizosphere of alpine pennycress (Noccaea caerulescens (J. Presl & C. Presl) F.K. Mey), maize (Zea mays L.) and ryegrass (Lolium perenne L.), when growing on three soils contaminated by trace metals with initial pH values varying from 5.6 to 7.4. The pH dynamics were recorded, using a recently developed 2D imaging technique based on planar pH optodes. This showed that alpine pennycress and ryegrass alkalinized their rhizosphere by up to 1.7 and 1.5 pH units, respectively, whereas maize acidified its rhizosphere by up to ?0.7 pH units. The alkalinization by the roots of alpine pennycress and ryegrass was permanent and not restricted to specific root zones, whereas the acidification along the maize roots was restricted to the elongation zone and thus only temporary. Calculations showed that such pH changes should have noticeable effects on the solubility of the trace metal in the rhizosphere, and therefore on their uptake by the plants. As a result, it is suggested that models for trace metal uptake should include precise knowledge of rhizospheric pH conditions.     

Drugs, bugs, and esophageal pH profiles

Until relatively recently, gastroesophageal reflux disease (GERD) was thought to be a relatively trivial problem, and pharmaceutical companies initially had remarkably little interest in clinical trials for GERD. Over the last ten years, GERD therapy has become the subject of intense interest, since reflux disease is now recognized as a major market for antisecretory and prokinetic drugs. Even low-technology antacids are now known to effectively neutralize esophageal acid prevent acid reflux for up to 90 minutes. Esophageal pH profiling is known to be an excellent surrogate for clinical efficacy of GERD drugs, particularly in erosive esophagitis. Years ago, famotidine normalized esophageal mucosal exposure to pH < 4.0 only when administered in doses of 40 mg twice a day. Subsequent studies confirmed that multiple daily dosing of histamine-2 receptor antagonists (H2RAs) was mandatory for GERD treatment, with clear dose-response relationships for each agent. Proton pump inhibitors (PPIs) have each been carefully assessed in terms esophageal and gastric pH profiles. Omeprazole has a particularly flat dose response curve, making it difficult to differentiate pH or clinical effects of 20 vs. 40 mg doses. Improved rapidity of onset and/or enhanced potency is demonstrable in pH data obtained with lansoprazole, rabeprazole and pantoprazole. Such differences will translate to improved clinical efficacy, based on the meta-analyses of Richard Hunt and his group in Canada that correlate pH effects and symptom relief/healing. PPI's have dependably surpassed H2RAs and prokinetic drugs in management of the more severe grades of esophagitis. Helicobacter pylori has a peculiar relationship to GERD. There has been some concern that PPIs given to patients with H. pylori might accelerate development of severe atrophic gastritis. It is also now known that eradication of H. pylori may increase symptomatic GERD (possibly as a result of increased gastric acid secretion once the bacteria have been eliminated). New data confirm nocturnal breakthrough of acid secretion and esophageal acid exposure in three-fourths of patients on omeprazole 20 mg twice daily. This nocturnal acidity can be controlled more effectively with a nighttime dose of an H2RA than with a third dose of omeprazole. Control of acid secretion and improved gastric and esophageal pH profiles are goals of modern GERD therapy, and the product that most cost effectively normalizes esophageal acid exposure will have a substantial advantage in the ever-growing GERD marketplace.     

BRAIN pH MEASUREMENTS USING A DIFFUSIBLE, LIPID SOLUBLE pH SENSITIVE FLUORESCENT INDICATOR

Brain tissue pH was measured in cats at normocapnia hypocapnia, hypercapnia, and death from anoxia using a pH sensitive fluorescent indicator (umbelliferone) with both molecular and ionic fluorophors. A ratio analysis of the indicator's calibrated 450 nm fluorescent tissue washout curves from 340 and 370 nm excitation permitted direct determinations using a nomogram. Possible errors in these measurements related to differential quenching, absorption, and changes in the redox state of the indicator were investigated in vitro and in vivo for brain tissue and blood. In animals with preserved autoregulation, brain pH varied linearly with arterial pH (art pH 7.0, brain pH 6.98: art pH 7.4, brain pH 7.24). Brain pH at death fell to 6.68. An analysis of the indicator clearance curves suggests these measurements reflect a component of the intracellular space and the lipid solubility of the indicator suggests this is a membranous component.     

Active transport,ion movements,and pH changes

The transport of substances across cell membranes may be the most fundamental activity of living things. When the substance transported is any ion there can be a change in the concentration of hydrogen ions on the two sides of the membrane. These hydrogen ion concentration changes are not caused by fluxes of hydrogen ions although fluxes of hydrogen ions may sometimes be involved. The reason for the apparent contradiction is quite simple. All aqueous systems are subject to two constraints: (1) to maintain the charge balance, the sum of the cationic charges must equal the sum of the anionic charges and (2) the product of the molar concentration of H⁺ and the molar concentration of OH⁻, established and maintained by the association and the dissociation of water, remains always at 10⁻¹⁴. As a consequence the concentrations of H⁺ and OH⁻ are determined uniquely by differences between the concentrations of the other cations and anions, with [H⁺] and [OH⁻] being dependent variables. Hydrogen ions and hydroxyl ions can be produced or consumed in local reactions whereas any strong ions such as Cl⁻, Mg²⁺, or K⁺ can be neither produced nor consumed in biological reactions. Further consequences of these truisms are outlined here in terms of the chemistry of the kinds of reactions which can lead to pH changes.     

Calcium, parathyroid hormone, oxytocin and pH profiles in the whelping bitch

Despite the high prevalence of primary uterine inertia in whelping bitches, the underlying pathogenesis remains unclear. The objectives were to i) determine serum concentrations of total calcium, ionized calcium (iCa), parathyroid hormone (PTH), and blood pH in normally whelping bitches throughout the peri-parturient period; and ii) investigate relationships among iCa, PTH, and acid-base status, and the role that they and oxytocin may have in the underlying pathogenesis of canine uterine inertia. Bitches were randomly selected from a population of German Shepherd Dog bitches with a history of uncomplicated parturition (Group 1; n = 10), and from a population of Labrador bitches with a clinical history of an increased incidence of uterine inertia and stillbirths (Group 2; n = 20). Jugular blood samples were collected daily from -4 d to the onset of whelping (t = 0 h), and then every 4 h until the last pup was born. Overall, bitches from Group 2 had higher mean ± SEM serum concentrations of PTH (4.72 ± 2.45 pmol/L, P < 0.001), lower iCa (1.31 ± 0.08 pmol/L, P < 0.05), and higher venous pH (7.41 ± 0.03, P < 0.005) than bitches from Group 1 (2.9 ± 1.44 pmol/L, 1.38 ± 0.06 mmol/L, and 7.33 ± 0.02, respectively) during the periparturient period. However, there was no significant difference between Groups 1 and 2 for serum oxytocin concentrations during the periparturient period (45.5 ± 40 and 65.5 ± 82 pg/mL). We inferred that low iCa resulting from a rising pH and decreasing PTH during the periparturient period may have contributed to decreased uterine contractility and increased risk of stillbirths. Therefore, manipulating the cationic/anionic difference in diets of pregnant bitches, similar to the bovine model for hypocalcamia, may reduce the incidence of stillbirths in the bitch.     

受体介导内吞对巨噬细胞膜电位、胞浆和溶酶体pH的影响

本文利用荧光标记方法测定了刀豆素Ａ、麦芽凝集素、酵母多糖刺激引起的巨噬细胞膜电位、胞浆ｐＨ溶酶体ｐＨ的变化。结果显示三种配体均导致细胞膜电位超极化,胞浆ｐＨ降低、溶酶体ｐＨ或高,三个生理参量趋于稳定时间稍有不同。胞浆ｐＨ的降低可能有抑制内吞的作用,溶酶体ｐＨ上升是触发溶酶体内容物外排的基本因素。内吞引起的这些变化是细胞代谢过程中自我调节和保护的表现。     

Glutamate transport into synaptic vesicles. Roles of membrane potential, pH gradient, and intravesicular pH.

Glutamate, the major excitatory neurotransmitter in the mammalian central nervous system, is transported into bovine synaptic vesicles in a manner that is ATP dependent and requires a vesicular electrochemical proton gradient. We studied the electrical and chemical elements of this driving force and evaluated the effects of chloride on transport. Increasing concentrations of Cl- were found to increase the steady-state ATP-dependent vesicular pH gradient (delta pH) and were found to concomitantly decrease the vesicular membrane potential (delta psi). Low millimolar chloride concentrations, which cause 3-6-fold stimulation of vesicular glutamate uptake, caused small but measurable increases in delta pH and decreases in delta psi, when compared to control vesicles in the absence of chloride. Nigericin in potassium buffers was used to alter the relative proportions of delta pH and delta psi. Compared to controls, at all chloride concentrations tested, nigericin virtually abolished delta pH and increased the vesicle interior positive delta psi. Concomitantly, nigericin increased ATP-dependent glutamate uptake in 0-1 mM chloride but decreased glutamate uptake in 4 mM (45%), 20 mM (80%), and 140 mM (75%) Cl- (where delta pH in the absence of nigericin was large). These findings suggest that either delta psi, delta pH, or a combination can drive glutamate uptake, but to different degrees. In the presence of 4 mM Cl-, where uptake is optimal, both delta psi and delta pH contribute to the driving force for uptake. When the extravesicular pH was increased from 7.4 to 8.0, more Cl- was required to stimulate vesicular glutamate uptake. In the absence of Cl-, as extravesicular pH was lowered to 6.8, uptake was over 3-fold greater than it was at pH 7.4. As extravesicular pH was reduced from 8.0 toward 6.8, less Cl- was required for maximal stimulation. Decreasing the extravesicular pH from 8.0 to 6.8 in the absence of Cl- significantly increased glutamate uptake activity, even though proton-pumping ATPase activity actually decreased about 45% under identical conditions. In the absence of chloride, nigericin increased glutamate uptake at all the pH values tested except pH 8.0. Glutamate uptake at pH 6.8 in the presence of nigericin was over 6-fold greater than uptake at pH 7.4 in the absence of nigericin. We conclude from these experiments that optimal ATP-dependent glutamate uptake requires a large delta psi and a small delta pH.(ABSTRACT TRUNCATED AT 400 WORDS)