Pronounced Acidification Research Articles

Spatiotemporal Variation and Influences of Acidification in the North Pacific, 1995–2019

The continuous rise in atmospheric CO2 levels has led to persistent ocean acidification, which negatively impacts marine environments crucial for marine life and alters the chemical composition of seawater. This phenomenon carries significant implications for human society. Utilizing surface seawater pH data from the North Pacific spanning 1995 to 2019, this study investigates the overall and localized spatiotemporal variations in pH within the region, as well as the factors influencing these variations. Additionally, it conducts a quantitative analysis of the different influencing factors. The findings reveal a consistent downward trend in surface seawater pH in the North Pacific, decreasing from 8.073 to 8.029, with notable seasonal variations. The highest pH values are recorded in winter, followed by spring, with lower values in autumn and summer. Spatially, the pH values are higher in the northwest and lower in the southeast, with the most pronounced acidification occurring in the central and western regions, while other areas exhibit more uniform acidification levels. Spatial correlation analysis indicates that surface seawater pH in the North Pacific generally shows a negative correlation with sea surface temperature (SST), salinity (SSS), and chlorophyll-a concentration (chl a) and a positive correlation with dissolved oxygen (DO). Among these factors, SST exerts the greatest influence on seawater pH, followed by DO and SSS. The degree of acidification varies across different regions, and the dominant influencing factors differ accordingly. In the equatorial central region (A), the primary factors are chl a and SST; in the eastern regions of China and Japan (B) and the western region of Canada (C), DO and SSS are the main controlling factors. An interaction analysis of each pair of dominant factors using the geodetector shows that their respective contributions to regions A, B, and C are 70%, 90%, and 50%, respectively. Understanding the primary factors driving acidification in different regions can aid in comprehending the biological and environmental impacts of acidification in those areas and provide valuable insights for mitigating marine acidification.

Responses of soil microbial communities and enzyme activities under nitrogen addition in fluvo-aquic and black soil of North China.

This research investigates the impact of long-term nitrogen (N) addition on fluvo-aquic and black soils in north China, with a focus on soil microbial communities and enzyme activities. In each site, there were three N fertilization treatments, i.e., control, moderate-N, and high-N. Phospholipid Fatty Acid Analysis was employed to analyze the microbial community composition, and enzyme activities related to N, carbon (C), and phosphorus (P) cycling were assessed. The results showed that increasing N fertilization levels led to higher soil organic carbon (SOC) and total N (TN) concentrations, indicating enhanced nutrient availability. N fertilization reduced soil pH across both soils, with a more pronounced acidification effect observed in the black soil. Across both soils, N addition increased maize yield, but the higher crop yield was attained in moderate-N rate compared with high-N rate. Microbial community composition analysis revealed that N fertilization induced shifts in the relative abundances of specific microbial groups. The black soil exhibited pronounced shifts in the microbial groups compared to the fluvo-aquic soil, i.e., decreased fungal abundance and fungi: bacteria ratio in response to N input. In addition, the application of N fertilizer led to an elevated ratio of gram-positive to gram-negative (GP:GN) bacteria, but this effect was observed only in black soil. N fertilization had an impact on the enzyme activities related to C, N, and P cycling in both soil types, but black soil showed more pronounced changes in enzyme activities. Permutational multivariate analysis of variance indicated that soil types rather than N fertilization mediated the response of the soil microbial community and enzyme activities. Partial least square path modeling demonstrated that soil pH was the only key driver impacting soil microbial groups and enzyme activities in both soils. In conclusion, our findings highlighted that N fertilization exerted more pronounced impacts on soil biochemical properties, microbial community composition, and enzyme activities in black soil furthermore, moderate N rate resulted in higher crop productivity over high N rate.

Agrogenic transformation (degradation) of chernozems of the Central Chernozem Region

Modern agriculture is impossible without the use of high balanced doses of mineral fertilizers. Mineral fertilizers in the modern volumes of their application are a powerful anthropogenic factor that increases the level of supply of agricultural crops with nutrients, but did not ensure the stability of yields. The long-term use of high doses of fertilizers does not allow to reach a deficit-free balance of fertilizer elements in agriculture and crop production. Studies of many scientists have shown that the long-term use of mineral fertilizers, in addition to the direct effect, causes a number of side effects, and contributes to the development of pronounced acidification of soils. This effect is observed in all agricultural zones, regardless of soil types. It is more pronounced on initially genetically acidic sod-podzolic and gray forest soils, but also on chernozems, which were considered resistant to acidification development. The consequences of soil acidification are manifested in the mobility and, as a result, the availability of fertilizer elements. Nevertheless, the main effect of soil acidification when using fertilizers is the lack of absorbed bases, which causes their progressive degradation. The acidification effect can be compensated by regular (once per rotation) liming.

Effects of forest harvest on soil nutrients and labile ions in Podzols of southwestern Canada: Mean and dispersion effects

Forest harvest can disrupt biogeochemical cycles with consequences for regenerating forest nutrition and drainage water quality. Few studies have examined harvest impacts on soil chemistry in conifer forests which have not been significantly affected by acid deposition, as found on the Canadian West Coast. This study investigates the effects of conventional clear-cutting on soil chemistry in Podzols of Roberts Creek Study Forest (southwestern Canada). We measured forest floor composition, soil pH and salt-extractable ions concentrations in undisturbed forested stands (control plots), stands harvested 2 to 5years prior to sampling (cleared plots) and stands harvested 8 to 15years prior to sampling (regenerating plots). We focused on the effects of forest harvest both on mean (differences in average values) and dispersion parameters (differences in variance between treatments).We found that forest floors of harvested plots had lower phosphorus and potassium concentrations than control plots. In the mineral subsoil, exchangeable K was however higher in harvested than in control plots. This suggests that some of the K lost from the forest floor was preferentially retained in mineral horizons, possibly due to sorption to poorly crystalline and free aluminum and iron mineral phases. The subsoil of harvested plots was slightly more acidic than control plots. In contrast to classic studies of forest harvest impacts conducted in the U.S. Northwest, we did not measure pronounced acidification, a loss of base cations or an increase in exchangeable Al, most likely due to the much lower prior acid deposition load at our sites. The most notable harvest effect was a large increase in the variability of inorganic N concentration. This suggests an increase in micro-heterogeneity of post-harvest nutrient availability which has implications for the nutrition of regenerating vegetation, nutrient leaching potential as well as our ability to detect harvest-induced changes.

Identification of pH‐sensitive currents in Drosophila sensory neurons

Acid‐sensing ion channels (ASIC) are proton‐gated Na+ channels that belong to the epithelial Na+ channel/degenerin (ENaC/Deg) superfamily. ASICs contribute to mechanosensation, nociception and synaptic plasticity. Pickpocket, PPK, are ENaC/Deg homologs in Drosophila neurons. We ask here whether PPK function as acid‐sensing channels with a view towards identify physiological function. Using whole cell patch‐clamping, we identified two acid‐sensing Na+ currents in multiple dendritic (md) neurons of Drosophila melanogaster. One current is robust and activated by pronounced acidification. Amiloride, a nonspecific antagonist of ENaC/Deg channels, reduces this pH‐sensitive current in a dose‐dependent manner. In addition, a distinct transient Na+ current (Na+tr) is present in md neurons. This current is activated by relief from inhibition subsequent to removal of amiloride following extracellular acidification. The standing acid‐sensing current was retained in md neurons of PPK−/− flies. In contrast, Na+tr was absent in md neurons of PPK−/− flies implying that PPK is part of the pH‐sensitive channel complex underlying this transient current. Phenotype assay of PPK−/− flies is clarifying the physiological role of PPK: preliminary results suggest a role in control of courtship behavior.

Deposition and Leaching of Sulfur, Nitrogen and Calcium in Four Forested Catchments in China: Implications for Acidification

Here we present the first detailed study on fluxes of sulfur (S), nitrogen (N), and major cations in Chinese subtropical forest catchments. Data are from four study sites, differing in inputs of atmospheric pollutants and sensitivity to acidification. Results show important differences from most sites in North America and Europe. Dry deposition of S, N, and calcium (Ca) is considerably larger than wet deposition in most cases causing deposition fluxes ranging from moderate to very high, both for acidifying compounds (S deposition 1.5-10.5 kiloequivalents per hectare and year (keq ha(-1) yr(-1)); N deposition 0.4 to 2.5 keq ha(-1) yr(-1)) and for alkaline compounds (Ca deposition 0.8 to 5.7 keq ha(-1) yr(-1)). More than half of the input of acidity is neutralized by alkalinity associated with Ca deposition. Furthermore, the retention of incoming S and N is small in the soil root zone, but considerable in the deeper soils or riparian zone. Drainage water from the root zone of the soils at the two sites with the highest deposition show pronounced acidification. For the two sites with moderate deposition inputs, the root zones are retaining some of the incoming S and buffer some of the incoming acidity. The subsoils and the riparian zonesare strong sinks for N, S, and Ca. This is associated with substantial acid neutralization at all sites. These features are of major importance for the understanding of the long-term effects of acidification in China.

Effects of acidification and increased extracellular potassium on dynamic muscle contractions in isolated rat muscles

Since accumulation of both H(+) and extracellular K(+) have been implicated in the reduction in dynamic contractile function during intense exercise, we investigated the effects of acidification and high K(+) on muscle power and the force-velocity relation in non-fatigued rat soleus muscles. Contractions were elicited by supramaximal electrical stimulation at 60 Hz. Force-velocity (FV) curves were obtained by fitting data on force and shortening velocity at different loads to the Hill equation. Acidification of the muscles by incubation with up to 24 mm lactic acid produced no significant changes in maximal power (P(max)) at 30 °C. More pronounced acidification, obtained by increasing CO(2) levels in the equilibration gas from 5% to 53%, markedly decreased P(max) and maximal isometric force (F(max)), increased the curvature of the FV relation, but left maximal shortening velocity (V(max)) unchanged. Increase of extracellular K(+) from 4 to 10 mm caused a depression of 58% in P(max) and 52% in F(max), but had no significant effect on V(max) or curvature of the FV curve. When muscles at 10 mM K(+) were acidified by 20 mm lactic acid, P(max) and F(max) recovered completely to the initial control level at 4 mm K(+). CO(2) acidification also induced significant recovery of dynamic contractions, but not entirely to control levels. These results demonstrate that in non-fatigued muscles severe acidification can be detrimental to dynamic contractile function, but in muscles depolarised by exposure to high extracellular [K(+)], approaching the [K(+)] level seen during intense fatiguing exercise, acidification can have positive protective effects on dynamic muscle function.

Endogenous Acidification of Central Inhibitory Synapses

In the brain, extracellular pH is rigidly maintained to ensure proper CNS function. To assess pH fluctuation at central synapses, we recorded miniature GABA inhibitory post-synaptic currents (mIPSCs) from cultured cerebellar granule cells under varying pH and proton buffering conditions. We found an inverse relationship between extracellular pH and mIPSC amplitude and charge transfer, resulting in over a 100% increase in size of events recorded at pH6.8 vs. pH8.0. Acidification also slowed the kinetics of rise time and fast component of decay, while speeding the slow decay component. We find that lowering the pH buffering capacity of the extracellular solution from 24 to 3mM HEPES at pH7.4, results in a similar enhancement of mIPSC size, mimicking changes in kinetics induced by acidification. The effects of diminished buffering capacity on mIPSC were negated by lowering extracellular pH to 6.8. To probe these effects with physiological buffers, we measured mIPSCs using 24mM of bicarbonate and compared them with those recorded in 24mM bicarbonate supplemented with 10mM HEPES . We found that physiological concentrations of bicarbonate produced mIPSCs that were similar in size and kinetics to those found with 3mM HEPES and were similarly altered with addition of HEPES, confirming the physiological relevance of our findings. To determine the possible contribution of Na+/H+ exchanger to synaptic acidification we inhibited the exchanger with amiloride (20μM), and in a parallel set of experiments replaced extracellular sodium with lithium. Both of these treatments caused changes in mIPSCs that mirrored increased buffering capacity, and the effects were negated by acidification to pH6.8 or by increasing HEPES buffering capacity to 24mM. We conclude that GABAergic synaptic pH in vivo may be quite labile and subject to rapid and pronounced acidification from the Na+/H+ exchanger with the net effect of enhancing synaptic transmission.

Soil Freezing and the Acid‐Base Chemistry of Soil Solutions in a Northern Hardwood Forest

Reductions in the depth and duration of snow cover under a warmer climate may cause soil freezing events to become more frequent, severe, and spatially extensive in northern temperate forest ecosystems. In this experiment, snow cover was manipulated to simulate the late development of snowpack and to induce soil freezing at sugar maple (Acer saccharum) and yellow birch (Betula alleghaniensis) stands at the Hubbard Brook Experimental Forest (HBEF) in the White Mountains of New Hampshire. The objective of this manipulation was to elucidate the effects of soil freezing on the concentrations and fluxes of soil solution H+, Ca2+, Mg2+, K+, and Na+, as well as values of acid neutralizing capacity (ANC). Mild soil freezing events (soil temperatures never decreased below −5°C) resulted in pronounced acidification of soil solutions, driven primarily by nitrification, in the forest floor of sugar maple stands during the growing season. This mobilization of NO−3 from the forest floor of maple stands was accompanied by the leaching of Ca2+ and Mg2+ in Oa horizon solutions. Responses of soil solution acid‐base chemistry to soil freezing were not evident in yellow birch stands or in the Bs horizon of either vegetation type, emphasizing the importance of vegetation type and the mineral soil in determining the effects of climatic disturbance on drainage water chemistry and nutrient loss. These results suggest that models of soil biogeochemistry in temperate forest ecosystems should consider soil‐freezing events when simulating the acid‐base chemistry of soil solutions and the translocation of nutrient base cations between soil horizons.

Loss of cell volume regulation during metabolic inhibition in renal epithelial cells (A6): role of intracellular pH.

In renal ischemia, tubular obstruction induced by swelling of epithelial cells might be an important mechanism for reduction of the glomerular filtration rate. We investigated ischemic cell swelling by examining volume regulation of A6 cells during metabolic inhibition (MI) induced by cyanide and 2-deoxyglucose. Changes in cell volume were monitored by recording cell thickness (T(c)). Intracellular pH (pH(c)) measurements were performed with the pH-sensitive probe 5-chloromethyl-fluoresceine diacetate. T(c) measurements showed that MI increases cell volume. Cell swelling during MI is proportional to the rate of Na(+) transport and is not followed by a volume regulatory response. Furthermore, MI prevents the regulatory volume decrease (RVD) elicited by a hyposmotic shock. MI induces a pronounced intracellular acidification that is conserved during a subsequent hypotonic shock. A transient acidification induced by a NH(4)Cl prepulse causes a marked delay of the RVD in response to a hypotonic shock. On the other hand, acute lowering of external pH to 5, simultaneously with the hypotonic shock, allowed the onset of RVD. However, this RVD was completely arrested approximately 10 min after the initiation of the hyposmotic challenge. The inhibition of RVD appears to be related to the pronounced acidification that occurred within this time period. In contrast, when external pH was lowered 20 min before the hyposmotic shock, RVD was absent. These data suggest that internal acidification inhibits cellular volume regulation in A6 cells. Therefore, the intracellular acidification associated with MI might at least partly account for the failure of volume regulation in swollen epithelial cells.

Vegetation changes during 100 years of development of two secondary woodlands on abandoned arable land

Broadbalk and Geescroft Wildernesses were abandoned as arable fields in the 1880s and allowed to develop with little further direct human intervention. Both have now developed into mature mixed deciduous woodland, variants of National Vegetation Classification type W8, Fraxinus excelsior — Acer campestre — Mercurialis perennis woodland. In addition, a portion of Broadbalk Wilderness has been maintained as grassland by removing woody colonists and, latterly, by grazing. The succession from arable to woodland has been recorded at irregular intervals for more than 100 years. Despite its limitations, this is the longest record of the floristic development of secondary woodland on farmland in the UK. Woody species colonised Broadbalk within 10 years, but at Geescroft they were not recorded until 30 years after abandonment. At present, both sites have good overstorey canopies with well developed understories which provide densely shaded conditions. There are currently 17 species of shrubs and trees at each site. The transition from a flora of mainly light-demanding species to shade tolerant species took place within 20–40 years of abandonment. The development of the shade flora within the woods has been characterised by: (1) a high turnover of species; (2) a failure to colonise by some shade-bearing species in the vicinity; and (3) inability of some colonists to spread beyond the wood margins. This appeared to be associated with: (1) dense shade from the closed woodland canopy; (2) competition from established ground flora dominants, particularly Hedera helix; (3) lack of suitable moist soils and open space habitats within the woods; and (4) pronounced acidification of soils in one wood. Some implications for new farm woodland creation are discussed.

Nutrient concentrations and acidity in ferralitic soil under perennial cropping, fallow and primary forest in central Amazonia

SummaryThe long‐term productivity on the acidic, nutrient‐poor upland soils of central Amazonia depends to a large extent on the chemical soil fertility as influenced by vegetation type and management. We compared soil and soil solution data from permanent cropping, fallow and primary forest on a Xanthic Ferralsol in central Amazonia to evaluate changes of soil fertility following forest conversion, agricultural use at different intensities and setting aside agricultural land. The agricultural systems included a perennial polyculture at two fertilizer inputs and a monoculture plantation. Soil and soil solution were collected to 2 m depth, and the soil solution was monitored over 2 years. Both soil and soil solution data showed decreasing soil fertility in the sequence: monoculture and polyculture at large input, polyculture at small input, forest and fallow. The soil solution data were more sensitive to effects of systems and fertilizer inputs on subsoil fertility. Fractionation of the N in the soil solution showed a larger proportion of dissolved organic N in the N‐poor fallow soil than in the soil under forest and agriculture. The soil under fallow, forest and low‐input agriculture had larger exchangeable acidity than that under high‐input agriculture, but the Al concentrations in the soil solution were very small because there were few cations with which to exchange and less nitrification. In high‐input agriculture, pronounced acidification peaks in the topsoil solution followed fertilization. The comparison of soil and soil solution data explained why the spontaneous vegetation thrives at very large exchangeable acidity in these soils, whereas agricultural systems often depend on liming to reduce the concentration of toxic Al in the soil.

Malignant gliomas display altered pH regulation by NHE1 compared with nontransformed astrocytes.

Malignant gliomas exhibit alkaline intracellular pH (pH(i)) and acidic extracellular pH (pH(e)) compared with nontransformed astrocytes, despite increased metabolic H(+) production. The acidic pH(e) limits the availability of HCO(-)(3), thereby reducing both passive and dynamic HCO(-)(3)-dependent buffering. This implies that gliomas are dependent upon dynamic HCO(-)(3)-independent H(+) buffering pathways such as the type 1 Na(+)/H(+) exchanger (NHE1). In this study, four rapidly proliferating gliomas exhibited significantly more alkaline steady-state pH(i) (pH(i) = 7.31-7.48) than normal astrocytes (pH(i) = 6.98), and increased rates of recovery from acidification, under nominally CO(2)/HCO(-)(3)-free conditions. Inhibition of NHE1 in the absence of CO(2)/HCO(-)(3) resulted in pronounced acidification of gliomas, whereas normal astrocytes were unaffected. When suspended in CO(2)/HCO(-)(3) medium astrocyte pH(i) increased, yet glioma pH(i) unexpectedly acidified, suggesting the presence of an HCO(-)(3)-dependent acid loading pathway. Nucleotide sequencing of NHE1 cDNA from the gliomas demonstrated that genetic alterations were not responsible for this altered NHE1 function. The data suggest that NHE1 activity is significantly elevated in gliomas and may provide a useful target for the development of tumor-selective therapies.

Effects of ischemia on skeletal muscle energy metabolism in mice lacking creatine kinase monitored by in vivo 31P nuclear magnetic resonance spectroscopy.

The aim of this study was to provide in vivo experimental evidence for the proposed biological significance of the creatine kinase (CK)/phosphocreatine (PCr) system in the energy metabolism of skeletal muscle. As a test system we compared hindlimb muscle of knockout mice lacking the cytosolic M-type (M-CK(-)/(-)), the mitochondrial ScMit-type (ScCKmit(-)/(-)), or both creatine kinase isoenzymes (CK(-)/(-)), and in vivo 31P-NMR was used to monitor metabolic responses during and after an ischemic period. Although single mutants show some subtle specific abnormalities, in general their metabolic responses appear similar to wild type, in contrast to CK(-)/(-) double mutants. This implies that presence of one CK isoform is both necessary and sufficient for the system to be functional in meeting ischemic stress conditions. The global ATP buffering role of the CK/PCr system became apparent in a 30% decline of ATP in the CK(-)/(-) mice during ischemia. Both M-CK(-)/(-) and CK(-)/(-) showed increased phosphomonoester levels during ischemia, most likely reflecting adaptation to a more efficient utilization of glycogenolysis. While in M-CK(-)/(-) muscle PCr can still be hydrolyzed to provide Pi for this process, in CK(-)/(-) muscle only Pi from ATP breakdown is available and Pi levels increase much more slowly. The experiments also revealed that the system plays a role in maintaining pH levels; the CK(-)/(-) mice showed a faster and more pronounced acidification (pH = 6.6) than muscles of wild type and single knockout mutants (pH = 6.9).

PH regulation of the globular substance in the otoconial membrane of the guinea-pig inner ear

Physiological and pharmacological characteristics of the globular substance, a precursor of otoconia, are not well understood. In the present study, we investigated the variations and regulation of internal pH (pH i) of the globular substance of the guinea-pig inner ear. The otoconial membrane was dissected out from the utricular macula and loaded with the pH-sensitive fluorophore, carboxy-seminaphthorhodafluor-1. Dynamic changes of fluorescence were directly observed under a confocal laser scanning microscope, and pH i was calculated from dual emission ratio. In the NaCl standard solution buffered with 5 mM HEPES/Tris at pH 7.4, the pH i of the globular substance varied from 6.26 to 8.55 with an average of 7.21 ( n=270). Exposure to 25 mM NH + 4 induced a rapid increase of the pH i followed by a slow relaxation. Then, wash-out of NH + 4 caused a prompt and pronounced acidification followed by a gradual pH i recovery to the initial level. This gradual pH i recovery was significantly inhibited by the absence of external Na +, indicating the presence of an external Na +-dependent H + extrusion mechanism. This pH i recovery was also inhibited by 1 mM amiloride and 10 μM 3-amino- N-(aminoiminomethyl)-6-[ethyl(2-propyl)amino]pyrazine-2-carboxamide. These results suggest the presence of an Na +-H + exchanger in the globular substance of the guinea pig. However, HCO − 3-transporting mechanisms were not determined. The working hypothesis for the otoconial formation is discussed.

Effect of drought experiments using roof installations on acidification/nitrification of soils

Within the framework of the EU-funded EXMAN (EXperimental MANipulation of Forest Ecosystems) project drought experiments were conducted at four different European Norway Spruce ( Picea abies (L.) Karst.) plantations in the year 1992–1995. The aim of the project was to investigate if there is an additional risk of soil acidification due to nitrification/acidification pulses after extended periods of summer droughts. The sites included (Ballyhooly/BH, southwest of Ireland. Klosterhede/KH, west coast of Denmark, Höglwald/HW, northwest of Munich, and Solling/SL, central Germany) cover considerable gradients of climatic and air pollution regimes. Artificial droughts were produced by using different types of roof constructions installed below the forest canopy (non-permanent constructions in BH and HW, permanent installations in KH and SL). Each drought was started in spring time and dry conditions were maintained until the soil water tension was below a potential of −700 hPa at 70 cm depth in the mineral soil. Results given are focused on changes in the soil solution concentrations during the rewetting of severely dried out soils. No marked nitrification pulses were observed after any of the droughts carried out at any site. Only single lysimeters/sample locations showed the hypothesized reaction with increasing aluminum concentrations and decreasing pH values, but spatial heterogeneity was high during rewetting. In the first soil solution samples after the drought, occasionally distinct peaks of NH 4 +, DOC and K +, and partly also N org and HPO 4 2− appeared. For the BH site the respective potassium concentrations increased 10 to 20 times compared to the level of the control plot. Presented data indicate a certain potential for nitrification pulses at the BH and KH site, but probably due to a fast root uptake, below the rooting zone no nitrate was determined. At the HW site, the drought induced reactions in the soil solution composition were only visible in humus water samples. At SL, nitrate concentrations were generally reduced at the drought plot. During rewetting in 1992 samples from a single lysimeter indicated a clear nitrification pulse. Applied flux calculations for SL showed a significant increase of the nitrate budget but a distinct decrease of the potassium budget. It is concluded that drought phases can influence the element cycling, but there seems to be no risk that forest soils will be subjected to pronounced acidification after summer droughts.

Effect of astroglial cell swelling on pH of acidic intracellular compartments

A variety of pathological conditions lead to swelling of astrocytes, which in turn stimulates ion release by activation of ion channels at the plasma membrane. In the present study, acridine orange and fluorescein isothiocyanate coupled to dextran (FITC-dextran) have been used to examine the effect of cell swelling on pH in acidic compartments of cultured astroglial cells. Both NH 4Cl (2 mM) and chloroquine (10 μM), known to alkalinize acidic cellular compartments, led to the expected increase in acridine orange fluorescence intensity. Similar, albeit smaller, effects were elicited by a reduction of extracellular osmolarity (−80 mOsm) and treatment of the cells with glutamate (1 mM), manoeuvres which enhanced cell volume. Determination of changes in the FITC-dextran fluorescence ratio ( 485 440 nm ) allowed quantification of the pH changes in lysosomal compartments. Treatment with NH 4Cl, reduced extracellular osmolarity and glutamate increased lysosomal pH by 0.65 ± 0.07, 0.85 ± 0.14 and 0.25 ± 0.07, respectively. Measurement of cytosolic pH using 2′,7′-bis-(2-carboxyethyl)-5- (and -6) carboxyfluorescein (BCECF) demonstrated a pronounced acidification following cell swelling, observed with both reduced extracellular osmolarity (by 0.23 ± 0.05 pH units) and 1 mM glutamate (by 0.26 ± 0.02 pH units). In conclusion, pH within lysosomes and possibly other acidic cellular compartments of astrocytes is increased by cell swelling, which may have important consequences for astrocyte function.

Transient Hydrogeological Controls on the Chemistry of a Seepage Lake

A solute mass balance method was used to estimate groundwater inflow and outflow rates for Nevins Lake, Michigan, a seepage lake in the upper peninsula that historically has shown extremely variable water chemistry compared with most other seepage lakes. A 4‐year study (1989–1992) of the hydrology and geochemistry of Nevins Lake and its contiguous groundwater system revealed that changes in the mass of dissolved solutes are the result of annual hydraulic gradient reversals. A pronounced acidification of Nevins Lake from 1986 to 1988 was likely caused by drought‐induced diminished groundwater inflow rates. In this study, dissolved calcium (the major cation in water of Nevins Lake, groundwater, and precipitation) was used for estimating mass flow rates. During the 1989–1992 period, Nevins Lake showed a reproducible annual cycle in calcium mass. Immediately following spring snowmelt and the resulting hydraulic gradient reversal, the mass of dissolved calcium in the lake increases rapidly, and then it decreases steadily throughout the summer and early fall, at which time the lake becomes hydraulically mounded and receives no groundwater inflow. Groundwater flow rates estimated by the solute mass balance method are sensitive to assumed solute concentrations in discharging groundwater. Pore water samples from the lake bed are shown to be more representative of water discharging to the lake than are samples from piezometers near the lake shore, but spatial and temporal variability in pore water chemistry must be considered. Stable isotope analyses (18O and 2H) of lake water, groundwater, and pore water samples show that water discharging to Nevins Lake in the spring is entirely recycled lake water, and no groundwater derived from terrestrial recharge reaches the lake. The conceptual model formulated during this study linking lake chemistry and the contiguous groundwater system and general groundwater flow patterns surrounding highly transient lake systems are likely transferable to other similar systems.

Ca inhibits adenylyl cyclase in turkey erythrocyte membranes in a calmodulin independent manner

The lipoxygenase (LO) inhibitors nordihydroguaiaretic acid (NDGA) and 16S-hydroxy-5,8,11,13-(Z,Z,Z,E)-eicosatetraenoic acid (15-HETE) have been found to suppress the rise in free cytoplasmic Ca2+ concentration ([Ca2+]i) induced by the Ca2+ ionophores ionomycin and A23187 in rat thymocytes. Bromophenacyl bromide (BPB), a phospholipase A2 (PLA2) inhibitor, produced a much weaker inhibitory effect, and indomethacin, a cyclo-oxygenase inhibitor, practically did not influence the [Ca2+]i response to ionomycin. These findings implicate the involvement of LO product(s) in the [Ca2+]i rise triggered by the Ca2+ ionophores. The contribution of the NDGA-sensitive component to the ionomycin-induced [Ca2+]i rise was significant in the ionomycin concentration range of 0.1 nM to 0.1 μM, whereas at higher doses of the ionophore it gradually diminished. By contrast, the [Ca2+]i rise induced by exogenous arachidonic acid (AA) or melittin, a PLA2 activator, was not suppressed but potentiated by NDGA. Ionomycin and exogenous AA also elicited opposite changes in thymocyte cytoplasmic pH (pHi): the former elevated the pHi while the latter induced a pronounced acidification of the cytoplasm. This difference in the pHi responses may account for the different sensitivity of ionomycin- and AA-elicited [Ca2+]i signal to LO inhibitors.

Holocene development and early extreme acidification in a small hilltop lake in southern Finland

The Holocene development of Pieni Majaslampi, a small hilltop lake which is exceptionally old for the conditions prevailing in southern Finland, is studied here by sedimentological and biostratigraphical methods. The lake is naturally acidic, with a pH of 4.5, and has been so since at least 8500 C14 BP, as determined from inferred‐pH techniques based on contemporary diatom‐pH relationships. The lake was found to have been subjected to extremely pronounced acidification during its early developmental stages, the pH having dropped from 5.8 to 4.7 between c. 10,000 and 8500 BP. Predicted pH values ranged from 4.5 to 5.1 over the remainder of its 8500‐year history. Low pH values of 4.5‐4.7 were found at the end of the Boreal Chronozone and in the Subboreal Chronozone and higher pH values of 4.7‐5.1 in the Atlantic and Subatlantic chronozones. This pattern is believed to reflect changes in macroclimate, particularly humidity. The rapid early acidification was shown in the cladoceran succession by the replacement of Bosmina longirostris by Bosmina (Eubosmina) longispina and by an increased number of species such as alonella nana and Alonella excisa. considerable shifts in diatom species composition and abundance were observed during the most recent times, but distributions indicate that all the abundant taxa most frequently occur under acidic conditions, suggesting that other factors in addition to pH may be responsible for the shifts.