Intracellular pH in one-cell mouse embryo differs between subcellular compartments and between interphase and mitosis

The pH-sensitive dual-emission fluorophore SNARF-1 coupled with a laser confocal microspectrofluorimeter was used to measure the internal pH (pHi) in different subcellular and subnuclear compartments of early mouse embryos. By this method we analysed the first cell cycle of naturally fertilised embryos in order to detect possible pHi changes correlated to cellular events, particularly the onset of replication or transcription and the first mitosis. Throughout interphase, significant differences of pHi were observed between cytoplasm and pronuclei, and, even more striking, between these compartments and nucleolus precursor bodies, whose pHi was systematically lower. We could detect significant pHi change neither during the replication phase nor at the onset of zygotic transcription, but pHi increased at the end of the one-cell stage in both cytoplasm and chromatin regions, a process that seemed specifically correlated with mitosis.

pH heterogeneity at intracellular and extracellular plasma membrane sites in HT29-C1 cell monolayers

In the colonic mucosa, short-chain fatty acids change intracellular pH (pH(i)) and extracellular pH (pH(e)). In this report, confocal microscopy and dual-emission ratio imaging of carboxyseminaphthorhodofluor-1 were used for direct evaluation of pH(i) and pH(e) in a simple model epithelium, HT29-C1 cells. Live cell imaging along the apical-to-basal axis of filter-grown cells allowed simultaneous measurement of pH in the aqueous environment near the apical membrane, the lateral membrane, and the basal membrane. Subapical cytoplasm reported the largest changes in pH(i) after isosmotic addition of 130 mM propionate or 30 mM NH(4)Cl. In resting cells and cells with an imposed acid load, lateral membranes had pH(i) values intermediate between the relatively acidic subapical region (pH 6.3-6.9) and the relatively alkaline basal pole of the cells (pH 7.4-7.1). Transcellular pH(i) gradients were diminished or eliminated during an induced alkaline load. Propionate differentially altered pH(e) near the apical membrane, in lateral intracellular spaces between adjacent cells, and near the basal membrane. Luminal or serosal propionate caused alkalinization of the cis compartment (where propionate was added) but acidification of the trans compartment only in response to luminal propionate. Addition of NH(4)Cl produced qualitatively opposite pH(e) excursions. The microscopic values of pH(i) and pH(e) can explain a portion of the selective activation of polarized Na/H exchangers observed in HT29-C1 cells in the presence of transepithelial propionate gradients.

Simultaneous monitoring of vascular contractility, intracellular pH and intracellular calcium in isolated rat mesenteric arteries; effects of weak bases

We report the first simultaneous measurements of pHi, [Ca2+]i and tension, upon alteration of pHi, in isolated rat mesenteric arteries loaded with both carboxy SNARF and indo-1. In these vessels (pre-contracted by 30 mM KCl) alterations of pHi, by addition and subsequent washout of weak bases, produced complicated effects on tone. Although the changes in contractility did not mirror the changes in pHi they were, at all times, accompanied by parallel changes in [Ca2+]i.

Imaging sustained dissipative patterns in the metabolism of individual living cells

Theoretical studies have predicted spatiotemporal organization of cell metabolism. Using a rapidly gated CCD camera, we demonstrate for the first time sustained traveling waves of NAD(P)H autofluorescence and protons in individual morphologically polarized living cells. Chemical concentration fronts moved in the direction of cell orientation, thus correlating dissipative structures with cell shape.

Activity-dependent intracellular acidification correlates with the duration of seizure activity

Synchronized neuronal activity (seizures) can appear in the presence or absence of synaptic transmission. Mechanisms of seizure initiation in each of these conditions have been studied, but relatively few studies have addressed seizure termination. In particular, how are seizures terminated in the absence of synaptic activity where there is no loss of excitatory drive or augmentation of inhibitory inputs? We have studied dynamic activity-dependent changes of intracellular pH in the absence of synaptic transmission using the fluorescent pH indicator carboxylseminaphthorhodafluo-1. During epileptiform activity we observed intracellular acidification, whereas between seizures the intracellular pH recovered. Experimental conditions that shortened the epileptiform discharge correlated with more rapid intracellular acidification. On the other hand, experimental manipulation of intracellular pH altered the duration of the seizure discharge, with acidification resulting in early termination of the epileptiform activity. These data show a direct relationship between the level of intracellular acidification and the duration of the seizures, suggesting that an intracellular pH-dependent process can terminate nonsynaptic neuronal synchronization.

Sorption and desorption of Eu and Yb on alumina: mechanisms and effect of fulvic acid

The effects of pH, ionic strength and FA (fulvic acid) on the sorption and desorption of Eu(III) and Yb(III) on alumina were respectively investigated by using batch technique and radiotracers 152 + 154Eu and 169Yb. The distribution coefficients for sorption and desorption of Eu on alumina at pH 4.4, 4.6 and 5.7 in 1 mol/l NaCl solutions as a function of solid phase concentration were determined in the presence or absence of FA. The effects of pH, FA and ionic strength on the distribution coefficients for sorption and desorption of Yb on alumina were determined in 0.01-2.0 mol/l NaNO3. It was found that pH and FA influenced the sorption of Eu(III) and Yb(III) on alumina greatly. A surface hydrolysis model can satisfactorily and qualitatively explain the observations on bare alumina. The competition among the complexations of surface free hydroxyl groups, soluble and sorbed fulvic acids can satisfactorily and qualitatively explain the observations on the coated alumina.

Protein kinase D inhibits plasma membrane Na(+)/H(+) exchanger activity

The regulation of plasma membrane Na(+)/H(+) exchanger (NHE) activity by protein kinase D (PKD), a novel protein kinase C- and phorbol ester-regulated kinase, was investigated. To determine the effect of PKD on NHE activity in vivo, intracellular pH (pH(i)) measurements were made in COS-7 cells by microepifluorescence using the pH indicator cSNARF-1. Cells were transfected with empty vector (control), wild-type PKD, or its kinase-deficient mutant PKD-K618M, together with green fluorescent protein (GFP). NHE activity, as reflected by the rate of acid efflux (J(H)), was determined in single GFP-positive cells following intracellular acidification. Overexpression of wild-type PKD had no significant effect on J(H) (3. 48 +/- 0.25 vs. 3.78 +/- 0.24 mM/min in control at pH(i) 7.0). In contrast, overexpression of PKD-K618M increased J(H) (5.31 +/- 0.57 mM/min at pH(i) 7.0; P < 0.05 vs. control). Transfection with these constructs produced similar effects also in A-10 cells, indicating that native PKD may have an inhibitory effect on NHE in both cell types, which is relieved by a dominant-negative action of PKD-K618M. Exposure of COS-7 cells to phorbol ester significantly increased J(H) in control cells but failed to do so in cells overexpressing either wild-type PKD (due to inhibition by the overexpressed PKD) or PKD-K618M (because basal J(H) was already near maximal). A fusion protein containing the cytosolic regulatory domain (amino acids 637-815) of NHE1 (the ubiquitous NHE isoform) was phosphorylated in vitro by wild-type PKD, but with low stoichiometry. These data suggest that PKD inhibits NHE activity, probably through an indirect mechanism, and represents a novel pathway in the regulation of the exchanger.

Dissolved organic matter inhibition of sonochemical degradation of aqueous polycyclic aromatic hydrocarbons

Sonochemical degradation of aqueous polycyclic aromatic hydrocarbons (PAHs) was found to be rapid in the absence of other dissolved compounds (k = 0.006-0.015 s-1). In the presence of 20 mg Cl-1 fulvic acid, first-order PAH degradation rate constants decreased from 2.3- to 3.7-fold. Similar results were obtained with added benzoic acid, a crude analog for fulvic acid. In natural waters, PAH degradation was almost completely inhibited. Analysis of the kinetic behavior and reaction products indicates that PAHs are most likely degraded through a radical cation mechanism. Hydroxyl radical appeared to play an insignificant role in the degradation. Inhibited degradation was probably the result of either altered cavitation processes or isolation of the PAH away from cavitation sites.

Intracellular pH regulation of CA1 neurons in Na(+)/H(+) isoform 1 mutant mice

To understand the role of Na(+)/H(+) exchanger 1 (NHE1) in intracellular pH (pH(i)) regulation and neuronal function, we took advantage of natural knockout mice lacking NHE1, the most ubiquitously and densely expressed NHE isoform in the central nervous system (CNS). CA1 neurons from both wild-type (WT) and NHE1 mutant mice were studied by continuous monitoring of pH(i), using the fluorescent indicator carboxy-seminaphthorhodafluor-1 (SNARF-1) and confocal microscopy. In the nominal absence of CO(2)/HCO(3)(-), steady-state pH(i) was higher in WT neurons than in mutant neurons. Using the NH(4)Cl prepulse technique, we also show that H(+) flux in WT neurons was much greater than in mutant neurons. The recovery from acid load was blocked in WT neurons, but not in mutant neurons, by removal of Na(+) from the extracellular solution or by using 100 microM 3-(methylsulfonyl-4-piperidino-benzoyl)-guanidine methanesulfonate (HOE 694) in HEPES buffer. Surprisingly, in the presence of CO(2)/HCO(3)(-), the difference in H(+) flux between WT and mutant mice was even more exaggerated, with a difference of more than 250 microM/s between them at pH 6.6. H(+) flux in CO(2)/HCO(3)(-) was responsive to diisothiocyanato-stilbene-2, 2'-disulfonate (DIDS) in the WT but not in the mutant. We conclude that (a) the absence of NHE1 in the mutant neurons tended to cause lower steady-state pH(i) and, perhaps more importantly, markedly reduced the rate of recovery from an acid load; and (b) this difference in the rate of recovery between mutant and WT neurons was surprisingly larger in the presence, rather than in the absence, of HCO(3)(-), indicating that the presence of NHE1 is essential for the regulation and/or functional expression of both HCO(3)(-)-dependent and -independent transporters in neurons.

Effects of phyllodulcin, hydrangenol, and their 8-O-glucosides, and thunberginols A and F from Hydrangea macrophylla SERINGE var. thunbergii MAKINO on passive cutaneous anaphylaxis reaction in rats

We examined the antiallergic effects of phyllodulcin, hydrangenol, and their 8-O-glucosides, and thunberginols A and F isolated from the processed leaves (Hydrangeae Dulcis Folium) and dried leaves of Hydrangea macrophylla SERINGE var. thunbergii MAKINO using the passive cutaneous anaphylaxis (PCA) reaction. With the exception of phyllodulcin, these constituents were found to significantly inhibit the PCA reaction. Although thunberginol A showed the most potent inhibitory effect, hydrangenol was considered to be the principal antiallergic component in the processed leaves, after taking into account their contents.

Structure-requirements of isocoumarins, phthalides, and stilbenes from Hydrangeae Dulcis Folium for inhibitory activity on histamine release from rat peritoneal mast cells

We examined the structure-activity relationships of isocoumarins, phthalides and stilbenes isolated from Hydrangeae Dulcis Folium and related compounds for the inhibition of histamine release in rat peritoneal mast cells. The activities of isocoumarins such as thunberginols A and B were more potent than those of dihydroisocoumarins such as hydrangenol and thunberginol G. The double bond at the 3-position seemed to be essential to potentiate the activity. The hydroxyl groups at the 8-, 3'- and 4'-positions of isocoumarin were essential for the activity, while the hydroxyl group at the 6-position was scarcely needed. Since the activities of benzylidenephthalides such as thunberginol F were more potent than those of hydramacrophyllols A and B, the presence of a double bond at the 3-position was needed to increase the activity. Moreover, the hydroxyl group at the 8-position was essential for the activity. On the time course study, thunberginols A, B and F completely inhibited histamine release by pretreatment at 100 microM for 1 to 15 min, whereas DSCG inhibited histamine release only following 1-min pretreatment at 1000 microM. These results suggested that the mechanisms of the inhibitory effect of thunberginols are different from that of DSCG.

Using hippocampal slices to study how aging alters ion regulation in brain tissue

Aging alters ion regulation in brain tissue. This article describes methods useful for studying such age-related changes in the rat hippocampal slice preparation. Topics considered include (a) selection of appropriate age groups of rats for aging studies, (b) a description of methods for preparing and maintaining hippocampal slices, (c) measurement of intracellular pH with the H+-sensitive dye carboxy-SNARF-1, and (d) measurement of extracellular pH and K+ with cation-selective microelectrodes.

Characterization of intracellular pH regulation in the guinea-pig ventricular myocyte

1. Intracellular pH was recorded fluorimetrically by using carboxy-SNARF-1, AM-loaded into superfused ventricular myocytes isolated from guinea-pig heart. Intracellular acid and base loads were induced experimentally and the changes of pHi used to estimate intracellular buffering power (beta). The rate of pHi recovery from acid or base loads was used, in conjunction with the measurements of beta, to estimate sarcolemmal transporter fluxes of acid equivalents. A combination of ion substitution and pharmacological inhibitors was used to dissect acid effluxes carried on Na+-H+ exchange (NHE) and Na+-HCO3- cotransport (NBC), and acid influxes carried on Cl--HCO3- exchange (AE) and Cl--OH- exchange (CHE). 2. The intracellular intrinsic buffering power (betai), estimated under CO2/HCO3--free conditions, varied inversely with pHi in a manner consistent with two principal intracellular buffers of differing concentration and pK. In CO2/HCO3--buffered conditions, intracellular buffering was roughly doubled. The size of the CO2-dependent component (betaCO2) was consistent with buffering in a cell fully open to CO2. Because the full value of betaCO2 develops slowly (2.5 min), it had to be measured under equilibrium conditions. The value of betaCO2 increased monotonically with pHi. 3. In 5 % CO2/HCO3--buffered conditions (pHo 7.40), acid extrusion on NHE and NBC increased as pHi was reduced, with the greater increase occurring through NHE at pHi < 6.90. Acid influx on AE and CHE increased as pHi was raised, with the greater increase occurring through AE at pHi > 7.15. At resting pHi (7.04-7.07), all four carriers were activated equally, albeit at a low rate (about 0.15 mM min-1). 4. The pHi dependence of flux through the transporters, in combination with the pHi and time dependence of intracellular buffering (betai + betaCO2), was used to predict mathematically the recovery of pHi following an intracellular acid or base load. Under several conditions the mathematical predictions compared well with experimental recordings, suggesting that the model of dual acid influx and acid efflux transporters is sufficient to account for pHi regulation in the cardiac cell. Key properties of the pHi control system are discussed.

pH and drug resistance. I. Functional expression of plasmalemmal V-type H+-ATPase in drug-resistant human breast carcinoma cell lines

A major obstacle for the effective treatment of cancer is the phenomenon of multidrug resistance (MDR) exhibited by many tumor cells. Many, but not all, MDR cells exhibit membrane-associated P-glycoprotein (P-gp), a drug efflux pump. However, most mechanisms of MDR are complex, employing P-gp in combination with other, ill-defined activities. Altered cytosolic pH (pHi) has been implicated to play a role in drug resistance. In the current study, we investigated mechanisms of pHi regulation in drug-sensitive (MCF-7/S) and drug-resistant human breast cancer cells. Of the drug-resistant lines, one contained P-gp (MCF-7/DOX; also referred to as MCF-7/D40) and one did not (MCF-7/MITOX). The resting steady-state pHi was similar in the three cell lines. In addition, in all the cell lines, HCO3- slightly acidified pHi and increased the rates of pHi recovery after an acid load, indicating the presence of anion exchanger (AE) activity. These data indicate that neither Na+/H+ exchange nor AE is differentially expressed in these cell lines. The presence of plasma membrane vacuolar-type H+-ATPase (pmV-ATPase) activity in these cell lines was then investigated. In the absence of Na+ and HCO3-, MCF-7/S cells did not recover from acid loads, whereas MCF-7/MITOX and MCF-7/DOX cells did. Furthermore, recovery of pHi was inhibited by bafilomycin A1 and NBD-Cl, potent V-ATPase inhibitors. Attempts to localize V-ATPase immunocytochemically at the plasma membranes of these cells were unsuccessful, indicating that V-ATPase is not statically resident at the plasma membrane. Consistent with this was the observation that release of endosomally trapped dextran was more rapid in the drug-resistant, compared with the drug-sensitive cells. Furthermore, the drug-resistant cells entrapped doxorubicin into intracellular vesicles whereas the drug-sensitive cells did not. Hence, it is hypothesized that the measured pmV-ATPase activity in the drug-resistant cells is a consequence of rapid endomembrane turnover. The potential impact of this behavior on drug resistance is examined in a companion manuscript.

Changes in intracellular Na+ and pH in rat heart during ischemia: role of Na+/H+ exchanger

The role of the Na+/H+ exchanger in rat hearts during ischemia and reperfusion was investigated by measurements of intracellular Na+ concentration ([Na+]i) and intracellular and extracellular pH. Under our standard conditions (2-Hz stimulation), 10 min of ischemia caused no significant rise in [Na+]i but an acidosis of 1.0 pH unit, suggesting that the Na+/H+ exchanger was inactive during ischemia. This was confirmed by showing that the Na+/H+ exchange inhibitor methylisobutyl amiloride (MIA) had no effect on [Na+]i or on intracellular pH during ischemia. However, there was a short-lived increase in [Na+]i of 8.2 +/- 0.6 mM on reperfusion, which was reduced by MIA, showing that the Na+/H+ exchanger became active on reperfusion. To investigate the role of metabolic changes, we measured [Na+]i during anoxia. The [Na+]i did not change during 10 min of anoxia, but there was a small, transient rise of [Na+]i on reoxygenation, which was inhibited by MIA. In addition, we show that the Na+/H+ exchanger, tested by sodium lactate exposure, was inhibited during anoxia. These results show that the Na+/H+ exchanger is inhibited during ischemia and anoxia, probably by an intracellular metabolic mechanism. The exchanger activates rapidly on reperfusion and can cause a rapid rise in [Na+]i.

A novel role for carbonic anhydrase: cytoplasmic pH gradient dissipation in mouse small intestinal enterocytes

1. The spatial and temporal distribution of intracellular H+ ions in response to activation of a proton-coupled dipeptide transporter localized at the apical pole of mouse small intestinal isolated enterocytes was investigated using intracellular carboxy-SNARF-1 fluorescence in combination with whole-cell microspectrofluorimetry or confocal microscopy. 2. In Hepes-buffered Tyrode solution, application of the dipeptide Phe-Ala (10 mM) to a single enterocyte reduced pHi locally in the apical submembranous space. After a short delay (8 s), a fall of pHi occurred more slowly at the basal pole. 3. In the presence of CO2/HCO3--buffered Tyrode solution, the apical and basal rates of acidification were not significantly different and the time delay was reduced to 1 s or less. 4. Following application of the carbonic anhydrase inhibitor acetazolamide (100 microM) in the presence of CO2/HCO3- buffer, addition of Phe-Ala once again produced a localized apical acidification that took 5 s to reach the basal pole. Basal acidification was slower than at the apical pole. 5. We conclude that acid influx due to proton-coupled dipeptide transport can lead to intracellular pH gradients and that intracellular carbonic anhydrase activity, by facilitating cytoplasmic H+ mobility, limits their magnitude and duration.

Inhibition of both Na/H and bicarbonate-dependent exchange is required to prevent recovery of intracellular pH in single cardiomyocytes exposed to metabolic stress

Although tight regulation of intracellular pH (pHi) is critical for the survival under stress, paradoxically a slowed recovery of pHi under hypoxic injury may be cardioprotective. In this study, we investigated the recovery of pHi after hypoxia-induced intracellular acidosis in cardiomyocytes loaded with the H+-sensitive dye SNARF-1. Exposure of single cardiomyocytes to 2,4-dinitrophenol (DNP), an inhibitor of mitochondrial oxidative phosphorylation, induced significant intracellular acidification. However, within 10-12 min upon removal of DNP, cardiomyocytes restituted their intracellular H+ concentration. The presence either of 5-N-ethyl-N-isopropylamiloride (EIPA) an inhibitor of Na/H antiporter, or 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), an inhibitor of bicarbonate-dependent exchange, did not modify the cellular response to DNP. But, combined use of EIPA and DIDS prevented the restitution of intracellular pH following removal of DNP. This study, thus, demonstrated, for the first time, that blockade of both Na/H and bicarbonate-dependent exchange is necessary and sufficient to maintain the hypoxia-induced intracellular acidification. Therefore, concomitant blockade of both pH-regulating mechanisms deserves to be further considered as a novel strategy against hypoxia-reoxygenation injury in the heart.

Antiaggregatory, antithrombotic effects of MS-180, a novel platelet glycoprotein IIb/IIIa receptor antagonist

The antiaggregatory and antithrombotic effects of (S)-(-)-ethyl[6-[4-(morpholinoformimidoyl)benzamido]-3,4-dihydro-2 H-1-benzo-pyran-3-yl]acetate hydrochloride (MS-180), a novel platelet glycoprotein IIb/IIIa receptor antagonist, were investigated. Ma-HCl, (S)-(-)-[6-[4-(Morpholinoformimidoyl)benzamido]-3,4-dihydro-2H-1-b enzopyran-3-yl]acetic acid hydrochloride, the hydrochloride salt of Ma (active metabolite), inhibited the binding of fibrinogen to immobilized human glycoprotein IIb/III receptor with an IC50 value of 0.12+/-0.03 nM without affecting binding to either fibronectin or vitronectin receptors. In anesthetized guinea pigs, intraduodenal administration of MS-180 caused dose-dependent inhibition of both ADP- and collagen-induced ex vivo platelet aggregation. At the same dosages, occluded thrombus formation and platelet release reactions were also markedly suppressed. In anesthetized dogs, the bleeding time was prolonged slightly even when submaximal inhibition (< 90%) of ex vivo platelet aggregation was achieved following i.v. administration of Ma-HCl. Aspirin (100 mg/kg) prolonged the bleeding time to the same extent as MS-180 (1 mg/kg), although it suppressed only collagen-induced platelet aggregation. Therefore, MS-180 may be clinically useful for the treatment of thrombotic diseases.

Clearance of large Ca2+ loads in a single smooth muscle cell: examination of the role of mitochondrial Ca2+ uptake and intracellular pH

Redistribution of cytosolic free Ca2+ following Ca2+ influx into the cytoplasm was studied in single smooth muscle cells isolated from guinea-pig urinary bladder. Voltage-clamped cells were loaded with a low-affinity fluorophore Indo-1FF. A decay of free intracellular Ca2+ ([Ca2+]i) after the termination of the depolarizing pulse (1 s from -50 mV to +20 mV) was fitted with a single exponential and the effect of various substances on the time constant was compared. At a holding potential of +80 mV the [Ca2+]i decay was 1.56 times slower compared to that at -50 mV suggesting the presence of a voltage-dependent process redistributing Ca2+. In the presence of cyclopiazonic acid (CPA, 10 microM), an inhibitor of sarco(endo)plasmatic Ca2+ pump (SERCa), the [Ca2+]i decay was 3.93 times slower than that in the absence of the inhibitor. Introduction of a polycation Ruthenium Red (RR) (20 microM), an inhibitor of the mitochondrial Ca2+ uniporter, into a cell or collapsing a transmitochondrial H+ gradient with the protonophore CCCP (2 microM) slowed down the [Ca2+]i decay 6.05-fold and 9.78-fold, respectively. The apparent amplitude of [Ca2+]i increments was also increased by CCCP. Increasing H+ buffering power in the intracellular solution from 10 mM to 40 mM of HEPES greatly reduced the effect of CCCP on [Ca2+]i decay. A further increase in HEPES concentration to 100 mM eliminated the effects of CCCP both on the time course of [Ca2+]i decay and on the amplitude of [Ca2+]i increment. Perfusion of RR together with 100 mM HEPES into the cytoplasm was without effect on the decay time course of [Ca2+]i. The effect of CPA on [Ca2+]i decay was also reduced in cells loaded with 100 mM HEPES; the time constant in the presence of CPA was slowed down by a factor of 2.18. Application of 10 mM Na(+)-butyrate to the cells loaded with 10 mM HEPES resulted in a slowing down of [Ca2+]i decay: the time constant was increased by a factor of 5.84. Measurement of intracellular pH with SNARF-1 confirmed cytoplasmic acidification during application of Na(+)-butyrate and CCCP. It is concluded that the contribution of mitochondrial Ca2+ uptake to the rapid [Ca2+]i decay is much less than could be extrapolated from action of protonophores in these smooth muscle cells. The results also demonstrate the importance of intracellular pH for Ca2+ handling in the cytoplasm of smooth muscle cells.

A potential application to the study of microscopic energy deposition in a solid by means of heavy charged-particle induced photochromic alterations in a tissue-equivalent matrix

A theoretical study was carried out to investigate the feasibility of using the radiation-induced colour decay of photochromic molecules embedded in a polymer matrix as a probe for studying the microscopic energy deposition of heavy charged particles (HCPs) in a tissue-equivalent solid. The theoretical treatment makes use of the radial dose distribution function as derived from gas-phase physics, together with the effects of the increase in temperature and of matrix degradation on the colour-decay kinetics of the photochromic molecules, according to empirical models derived for the solid state. Bearing in mind the non-stochastic nature of the model, the use of gas-phase physics at the level of radiation interaction, and the fact that some empirical quantities used have been established macroscopically, all factors which signify that extra caution is required in the interpretation of the results, it is shown that when the optimum information retrieval time (after track formation) is considered the technique may be able to resolve differences in the energy deposition pattern by different HCPs in the nanometre range (1-10 nm; material's mass density 1.2 g cm(-3)) from the track axis. Most importantly, though, the present study aims to erect a theoretical framework for the possible application of the technique and to highlight those aspects which are likely to be critical to its practical usage, such as particle type and energy range, and spatial scale and magnitude of the expected effect together with its dependence on time, the physical characteristics of the matrix, and the kinetic behaviour of the type of photochromic molecule studied. Furthermore, it establishes a rationale for interpreting the experimentally observed (if available) colour changes in the HCP track in terms of the microscopic distribution of energy deposition in it.

Regulation of intracellular pH gradients by identified Na/H exchanger isoforms and a short-chain fatty acid

Colonic luminal short-chain fatty acids (SCFA) stimulate electroneutral sodium absorption via activation of apical Na/H exchange. HT29-C1 cells were used previously to demonstrate that transepithelial SCFA gradients selectively activate polarized Na/H exchangers. Fluorometry and confocal microscopy (with BCECF and carboxy SNARF-1, respectively) are used to measure intracellular pH (pHi) in HT29-C1 cells, to find out which Na/H exchanger isoforms are expressed and if results are due to pHi gradients. Inhibition of Na/H exchange by HOE-694 identified 1) two inhibitory sites [50% inhibitory dose (ID50) = 1.6 and 0.05 microM] in suspended cells and 2) one inhibitory site each in the apical and basolateral membranes of filter-attached cells (apical ID50 = 1.4 microM, basolateral ID50 = 0.3 microM). RT-PCR detected mRNA of Na/H exchanger isoforms NHE1 and NHE2 but not of NHE3. Confocal microscopy of filter-attached cells reported HOE-694-sensitive pHi recovery in response to luminal or serosal 130 mM propionate. Confocal analysis along the apical-to-basal axis revealed that 1) luminal or serosal propionate establishes transcellular pHi gradients and 2) the predominant site of pHi acidification and pHi recovery is the apical portion of cells. Luminal propionate produced a significantly greater acidification of the apical vs. basal portion of the cell (compared with serosal propionate), but no other dependence on the orientation of the SCFA gradient was observed. Results provide direct evidence for a subcellular response that assures robust activation of apical NHE2 and dampening of basolateral NHE1 during pHi regulation.