Changes in oxygen consumption and nitrogen metabolism in the dragonfly Somatochlora cingulata exposed to aluminum in acid waters

Oxygen consumption, ammonia excretion and changes in O:N ratios by the dragonfly Somatochlora cingulata were measured in four nymphal growth stages, relative to aluminum concentrations and low pH. A differential reduction in respiration and ammonia excretion rates resulted in an increase in ON ratios for all nymphal stages. The earlier stages, however, were the most sensitive. The ratios obtained were indicative of a decreased dependence on protein reserves and increased utilization of carbohydrates or lipid reserves. Also observed was an increase in the haemolymph pH and glutamate levels with a concomitant accumulation of tissue ammonia.     

Photosynthetically elevated pH in acid waters with high nutrient content and its significance for the zooplankton community

The pH of undisturbed surface waters in the New Jersey Pine Barrens is very acidic (pH 3.5–4.5). Surface waters disturbed by residential and agricultural development typically exhibit significantly elevated pH. Detailed analyses of a disturbed and undisturbed pond showed that the elevated pH of the disturbed pond was primarily the result of enhanced primary productivity. At night and during the winter, when productivity was reduced, the pH dropped to levels more characteristic of the undisturbed pond. The phenomenon of fluctuating pH had significant implications for the zooplankton in the disturbed pond. Though nutrients were significantly greater in the disturbed pond, zooplankton species composition and general abundance patterns were nearly identical in the two ponds. Thus, in these and other poorly buffered waters, it is hypothesized that the lowest pH values were the ones effectively regulating the zooplankton community.     

Interactions of temperature and pH on the regulatory properties of pyruvate kinase from organs of a marine mollusc

The effects of low temperature assay (5 °C) on the properties of the aerobic (low phosphate) vs. anoxic (high phosphate) forms of pyruvate kinase (PK) from foot muscle and gill of the whelk Busycon canaliculatum (L.) were assessed at two pH values, pH 7.00 and 7.25, and compared to control conditions of 20 °C and pH 7.00 (all assayed in imidazole buffer). When pH was held constant at 7.00, the decrease in assay temperature to 5 °C had large effects on the measured kinetic parameters of all PK forms, as compared to 20 °C and pH 7.00. However, when assay pH was allowed to rise, from 7.00 to 7.25, with the temperature decrease to 5 °C there were fewer alterations of kinetic parameters and quantitatively smaller changes to enzyme properties. It appears, then, that when pH rises with decreasing temperature following alphastat predictions, kinetic properties of PK are largely conserved. Low temperature, at either pH value, had several significant effects on PK properties. For example, low temperature raised the S_0.5 for phosphoenolpyruvate of PK-anoxic from gill by 3–6 fold and decreased the I₅₀ Mg · ATP for PK-anoxic from foot by the same amount. Arrhenius plots of PK activity for the gill PK forms showed a distinct break at 10 °C; > 10 °C Q₁₀ was 2.5 whereas < 10 °C Q₁₀ was 8.4. Temperature-dependent changes in all cases affected enzyme properties in a manner that would restrict enzyme function at low temperature.     

Lowering extracellular sodium or pH raises intracellular calcium in gastric cells

Summary The dependence of cytoplasmic free [Ca] (Ca _i ) on [Na] and pH was assessed in individual parietal cells of intact rabbit gastric glands by microfluorimetry of fura-2. Lowering extracellular [Na] (Na _o ) to 20mm or below caused a biphasic Ca _i increase which consisted of both release of intracellular Ca stores and Ca entry across the plasma membrane. The Ca increase was not blocked by antagonists of Ca-mobilizing receptors (atropine or cimetidine) and was independent of the replacement cation. Experiments in Ca-free media and in Na-depleted cells indicated that neither phase was due to reversal of Na/Ca exchange. The steep dependence of the Ca _i increase on Na _o suggested that the response was not due to lowering intracellular [Na] (Na _i ). The effects of low Na _o on Ca _i were also completely independent of changes in intracellular pH (pH _i ). Ca _i was remarkably stable during changes of pH _i of up to 2 pH units, indicating that H and Ca do not share a cytoplasmic buffer system. Such large pH excursions required determination of the pH dependence of fura-2. Because fura-2 was found to decrease its affinity for Ca as pH decreased below 6.7, corrections were applied to experiments in which large pH _i changes were observed. In contrast to the relative insensitivity of Ca _i to changes in pH _i , decreasing extracellular pH (pH _o ) to 6.0 or below was found to stimulate release of intracellular Ca stores. Increased Ca entry was not observed in this case. The ability of decreases in Na _o and pH _o to stimulate release of intracellular Ca stores suggest interactions between Na and H with extracellular receptors.     

Nitrate and chloride ions have different permeation pathways in skeletal muscle fibers ofRana pipiens

Summary The effects of pH on the permeability and conductance of the membranes to nitrate and to chloride of semitendinosus and lumbricalis muscle fibers were examined.Membrane potential responses to quick solution changes were recorded in semitendinosus fibers initially equilibrated in isotonic, high K₂SO₄ solutions. External solutions were first changed to ones in which either Rb⁺ or Cs⁺ replaced K⁺ and then to solutions containing either NO ₃ ^– or Cl^– to replace SO ₄ ^2– . The hyperpolarizations produced by Cl^– depend on external pH, being smaller in acid than in alkaline solutions. By contrast, hyperpolarizations produced by NO ₃ ^– were independent of external pH over a pH range from 5.5 to 9.0.In addition, voltage-clamp measurements were made on short lumbricalis muscle fibers. Initially they were equilibrated in isotonic solutions containing mainly K₂SO₄ plus Na₂SO₄. KCl or KNO₃ were added to the sulfate solutions and the fibers were equilibrated in these new solutions. When finally equilibrated the fibers had the same volume they had in the sulfate solutions before the additions. Constant hyperpolarizing voltage pulses of 0.6-sec duration were applied when all external K⁺ was replaced by TEA⁺. For these conditions, inward currents flowing during the voltage pulses were largely carried by Cl^– or NO ₃ ^– depending on the final equilibrating solution. Cl^– currents during voltage pulses were both external pH and time dependent. By contrast, NO ₃ ^– currents were independent of both external pH and time.The voltage dependence of NO ₃ ^– currents could be fit by constant field equations with aP _{NO 3} of 3.7·10^–6 cm/sec. The voltage dependence of the initial or instantaneous Cl^– currents at pH 7.5 and 9.0 could also be fit by constant field equations with P_Cl of 5.8·10^–6 and 7.9·10^–6 cm/sec, respectively. At pH 5.0, no measurable instantaneous Cl^– currents were found.From these results we conclude that NO ₃ ^– does not pass through the pH, time-dependent Cl^– channels but rather passes through a distinct set of channels. Furthermore, Cl^– ions do not appear to pass through the channels which allow NO ₃ ^– through. Consequently, the measured ratio ofP _Cl/P _{NO 3} based on membrane potential changes to ionic changes made on intact skeletal muscle fibers is not a measure of the selectivity of a single anion channel but rather is a measure of the relative amounts of different channel types.     

pH-stat experiments in proximal renal tubules

Summary The pH-stat technique has been used to measure H⁺ fluxes in gastric mucosa and urinary bladder in vitro while keeping mucosal pH constant. We now report application of this method in renal tubules. We perfused proximal tubules with double-barreled micropipettes, blocked luminal fluid columns with oil and used a double-barreled Sb/reference microelectrode to measure pH, and Sb or 1n HC1-filled microelectrodes to inject OH^– or H⁺ ions into the tubule lumen. By varying current injection, pH was kept constant at adjustable levels by an electronic clamping circuit. We could thus obtain ratios of current (nA) to pH change (apparent H⁺-ion conductance). These ratios were reduced after luminal 10^–4 m acetazolamide, during injection of OH^–, but they increased during injection of H⁺. The point-like injection source causes pH to fall off with distance from the injecting electrode tip even in oil-blocked segments. Therefore, a method analogous to cable analysis was used to obtain H⁺ fluxes per cm² epithelium. The relation betweenJ _H ⁺ and pH gradient showed saturation kinetics of H fluxes, both during OH^– and H⁺ injection. This kinetic behavior is compatible with inhibition ofJ _H by luminal H⁺. It is also compatible with dependence on Na⁺ and H⁺ gradients of a saturable Na/H exchanger. H⁺-ion back-flux into the tubule lumen also showed saturation kinetics. This suggests that H⁺ flow is mediated by a membrane component, most likely the Na⁺–H⁺ exchanger.     

Sodium/Proton Exchange in Cultured Bovine Adrenal Medullary Cells

We investigated the presence of Na+/H+ exchange in cultured bovine adrenal medullary cells. The intracellular pH in control cells measured by 5,5-dimethyl[2-14C]oxazolidine-2,4-dione was 7.13 +/- 0.02 (n = 6). Removal of Na+ from the incubation medium shifted the intracellular pH down to 6.67 +/- 0.12 (n = 6). Reintroduction of Na+ to the medium caused a rapid recovery in intracellular pH to 7.20-7.30 that was associated with an increase in uptake of 22Na+ by the cells. Both increases in intracellular pH and uptake of 22Na+ were inhibited by amiloride, an inhibitor of Na+/H+ exchange. The recovery of intracellular pH by addition of Na+ was partially inhibited by quinidine, another inhibitor of Na+/H+ exchange, but not by 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid, an anion-exchange (Cl-/HCO3-) inhibitor. Li+ could substitute for Na+ in the recovery of intracellular pH. Carbachol caused an increase in intracellular pH from 7.12 +/- 0.01 to 7.21 +/- 0.02 (n = 10). This increase in intracellular pH caused by carbachol was inhibited by amiloride. These results suggest the existence of an amiloride-sensitive Na+/H+ exchange that regulates the intracellular pH in adrenal medullary cells.     

The influence of lime and biological activity on sediment pH,redox and phosphorous dynamics

The addition of powdered limestone to intact sediment cores from oligotrophic, acid Lake Hovvatn caused pH to increase, redox potential (E₇) to drop, and permitted net precipitation of phosphorous (P) from the water column. Significant pH increase was found to a sediment depth of 6 cm and a maximum increase in pH from 4.9 to 6.5 was found at a depth of 0.5 cm when dosed with 36 g m^–2 of lime. Such pH increase creates important changes in sediment equilibrium chemistry and enhances habitat suitability. In the case of Hovvatn, however, sediments would consume only 5 kg of the 91 tons of applied limestone. Superficial sediments remained oxidized, but below 0.5 cm, E₇ in limed sediment declined significantly more than in unlimed sediments, with a maximum difference of 102 mV versus –66 mV at a depth of 6 cm in unlimed and limed cores, respectively. Abiotic reactions account for 82 ± 54% of this reduction and the remainder is due to the oxidation of organic matter by bacteria. Precipitation of CaSO₄, reduction of the sediments by organic compounds at elevated pH and inhibition of the downward diffusion of O₂ by the limestone powder are potential abiotic mechanisms which could drive E₇ down. Enhanced P release was not found at lowered E₇, and supernatent TP concentrations dropped from 11.7 to 4.4 µg P l^–1. More P was swept from solution in cores which recieved larger lime doses. The presence of chironomids caused sediment pH to increase by as much as 1.2 pH units, presumably due to NH₄ release, reduced sediment E₇ by as much as 171 mV and facilitated TP release during the first 17 d of core incubation. Field measurements of vertical distributions of sediment pH and E₇ before and after the liming of Hovvtn corroborated laboratory findings.     

Nitrogen fixation of lucerne (Medicago sativa) in an acid soil: The use of rhizotrons as a model system to simulate field conditions

The effect of pelleting seeds of lucerne with lime was studied in an acid sandy soil. In pot experiments, the fraction of seedlings with crown nodules, i.e. nodules on the upper 10 mm of the taproot, increased from 26% to 71%. In rhizotrons, the application of CaCO₃ resulted in an even stronger response.An agar-contact method was used to study pH changes in the rhizosphere during a period up to 12 days. Application of 1.0 µmol of CaCO₃, in drops of 12 µL volume, resulted in an initial soil pH of 6.1 and yielded 75% crown nodulation. In the absence of CaCO₃, roots induced a pH increase from 5.1 (day 0) to 5.7 (day 12). However, this did not increase nodulation (5%). Obviously, this type of alkalinization does not overcome the acid-sensitive step of the nodulation process.