Effect Of pHo Research Articles

Simultaneous removal of Pb2+ and direct red 31 dye from contaminated water using N-(2-hydroxyethyl)-2-oxo-2H-chromene-3-carboxamide loaded chitosan nanoparticles.

This study reports the preparation of a new material that can remove synthetic dyes and trace metals simultaneously. A new coumarin derivative was synthesized and its chemical structure was inferred from spectral data (FT-IR, 1H-NMR, 13C-NMR). Meanwhile, chitosan nanoparticles (CsNPs) were prepared then used as a carrier for two different concentrations of the coumarin derivative (C1@CsNPs and C2@CsNPs). The TEM, SEM and DLS findings illustrated that the prepared nanocomposites exhibited spherical shape and small size (less than 200 nm). The performance of the prepared material for the removal of an anionic dye (direct red 31, DR31) and cationic trace metal (Pb2+) was evaluated in unary and binary systems. The results revealed that complete removal of 10 mg L−1 of DR31 and Pb2+ in unary system was achieved at pHo 3.0 and 5.5 using 0.5 and 2.0 g L−1, respectively, of C2@CsNPs. The adsorption of DR31 and Pb2+ followed different mechanisms as deduced from the effect of pHo, kinetic, isotherm and binary adsorption studies. The adsorption of DR31 followed the Langmuir isotherm model and the pseudo-first-order kinetic model. While, the adsorption of Pb2+ followed Freundlich isotherm model and Elovich kinetic model. In the binary system, the co-presence of DR31 and Pb2+ did not affect the adsorption of each other's. Overall, the prepared material showed promising results for the removal of anionic dyes and cations trace metals from contaminated water.

Effects of pH on vascular tone in rabbit basilar arteries.

Effects of pH on vascular tone and L-type Ca2+ channels were investigated using Mulvany myograph and voltage-clamp technique in rabbit basilar arteries. In rabbitbasilar arteries, high K+ produced tonic contractions by 11±0.6 mN (mean±S.E., n=19). When extracellular pH (pHo) was changed from control 7.4 to 7.9 ([alkalosis]o), K+-induced contraction was increased to 128±2.1% of the control (n=13). However, K+-induced contraction was decreased to 73±1.3% of the control at pHo 6.8 ([acidosis]o, n=4). Histamine (10 µM) also produced tonic contraction by 11±0.6 mN (n=17), which was blocked by post-application of nicardipine (1 µM). [alkalosis]o and [acidosis]o increased or decreased histamine-induced contraction to 134±5.7% and 27±7.6% of the control (n=4, 6). Since high K+- and histamine-induced tonic contractions were affected by nicardipine and pHo, the effect of pHo on voltage-dependent L-type Ca2+ channel (VDCCL) was studied. VDCCL was modulated by pHo: the peak value of Ca2+ channel current (IBa) at a holding of 0 mV decreased in [acidosis]o by 41±8.8%, whereas that increased in [alkalosis]o by 35±2.1% (n=3). These results suggested that the external pH regulates vascular tone partly via the modulation of VDCC in rabbit basilar arteries.

Functionally-distinct proton-binding in HERG suggests the presence of two binding sites.

HERG (Human ether-à-go-go-related gene) potassium channels are crucial for cardiac action potential repolarization. HERG channels are also found in neuronal and tumor cells. The effect of pHo on HERG is of clinical significance because of changes in pH during myocardial ischemia, inflammation, and respiratory alkalosis. We present evidence for the presence of multiple proton binding sites in HERG. Extracellular protons bind rapidly and reversibly to affect both activation and deactivation. However, these effects occur in two distinct pHo ranges. The deactivation rate has a pKa of 6.76 +/- 0.02 compared to pKa of 5.50 +/- 0.02 for changes in current suppression, which suggests the presence of at least two proton binding sites on HERG with functionally distinct properties.

Molecular dissection of gating in the ClC-2 chloride channel.

The ClC-2 chloride channel is probably involved in the regulation of cell volume and of neuronal excitability. Site-directed mutagenesis was used to understand ClC-2 activation in response to cell swelling, hyperpolarization and acidic extracellular pH. Similar to equivalent mutations in ClC-0, neutralizing Lys566 at the end of the transmembrane domains results in outward rectification and a shift in voltage dependence, but leaves the basic gating mechanism, including swelling activation, intact. In contrast, mutations in the cytoplasmic loop between transmembrane domains D7 and D8 abolish all three modes of activation by constitutively opening the channel without changing its pore properties. These effects resemble those observed with deletions of an amino-terminal inactivation domain, and suggest that it may act as its receptor. Such a 'ball-and-chain' type mechanism may act as a final pathway in the activation of ClC-2 elicited by several stimuli.

Intracellular pH regulation in chicken enterocytes: the importance of extracellular pH

The present work reports the effect of pHo on pHi and Na(+)-H+ exchanger activity. Intracellular pH tended to follow pHo, but the proton distribution across the cell membrane is not at electrochemical equilibrium. Removal of external Na+ acidified the cells by both reversing the direction of the Na(+)-H+ exchanger and hyperpolarizing the cell membrane potential. The relationship between pHo and the rate of Na(+)-dependent proton efflux following an acid load suggests that external protons interact with the Na(+)-H+ exchanger at a single site with an apparent pK (-log of the dissociation constant) of 7.22. The results demonstrate that maintenance of pHo in the physiological range is essential for maintenance of normal cell pH and that the activity of the Na(+)-H+ exchanger involved in pHi regulation is affected by external protons. The results also suggest that, at least at low pHo, some intracellular mechanism is involved in pHi regulation.

Extracellular H+ modulates acetylcholine-activated nonselective cation channels in guinea pig ileum

The effects of external H+ on the acetylcholine-induced inward current (nonselective cationic current; InsACh) in guinea pig ileal smooth muscle were investigated using the conventional whole cell patch-clamp technique. When the external pH (pHo) was lowered, the amplitude of InsACh was increased, with no significant change in the reversal potential or no detectable induction of other ionic permeabilities. The dose-response curve for this effect was best described by a Hill-type equation with an apparent pKa value of 7.4 and a Hill coefficient of approximately 1. The effect of pHo was associated with a shift of the steady-state activation curve for InsACh; the half-maximum activation potential became more negative on lowering pHo. Similar results were obtained when InsACh was activated by intracellularly applied guanosine 5'-O-(3-thiotriphosphate). These results indicate that the external H+ activity is an efficient regulator of InsACh channel, and this may have a physiological importance for controlling the muscarinic receptor-mediated contractions in this muscle.

Effect of PbO on zinc electrodeposition from zincate solutions

The effect of PhO on zinc electrodeposition on a copper substrate from zincate solutions was investigated using cyclic voltammetry and by polarization measurements as a function of time. It was found that lead deposition caused the zinc deposition potential to cathodically shift by 100 mV in the negative direction. It is suggested that the presence of lead on the copper substrate suppresses hydrogen absorption and consequently inhibits zinc deposition via a path such as $$\left( {ZnOH} \right)_{ad} + H_{ad} \to Zn + H_2 O$$ .

Apical membrane Na+/H+ exchange in Necturus gallbladder epithelium. Its dependence on extracellular and intracellular pH and on external Na+ concentration.

Intracellular microelectrode techniques and extracellular pH measurements were used to study the dependence of apical Na+/H+ exchange on mucosal and intracellular pH and on mucosal solution Na+ concentration ([Na+]o). When mucosal solution pH (pHo) was decreased in gallbladders bathed in Na(+)-containing solutions, aNai fell. The effect of pHo is consistent with titration of a single site with an apparent pK of 6.29. In Na(+)-depleted tissues, increasing [Na+]o from 0 to values ranging from 2.5 to 110 mM increased aNai; the relationship was well described by Michaelis-Menten kinetics. The apparent Km was 15 mM at pHo 7.5 and increased to 134 mM at pHo 6.5, without change in Vmax. In Na(+)-depleted gallbladders, elevating [Na+]o from 0 to 25 mM increased aNai and pHi and caused acidification of a poorly buffered mucosal solution upon stopping the superfusion; lowering pHo inhibited both apical Na+ entry and mucosal solution acidification. Both effects can be ascribed to titration of a single site; the apparent pK's were 7.2 and 7.4, respectively. Diethylpyrocarbonate (DEPC), a histidine-specific reagent, reduced mucosal acidification by 58 +/- 4 or 39 +/- 6% when exposure to the drug was at pHo 7.5 or 6.5, respectively. Amiloride (1 mM) did not protect against the DEPC inhibition, but reduced both apical Na+ entry and mucosal acidification by 63 +/- 5 and 65 +/- 9%, respectively. In the Na(+)-depleted tissues mean pHi was 6.7. Cells were alkalinized by exposure to mucosal solutions containing high concentrations of nicotine or methylamine. Estimates of apical Na+ entry at varying pHi, upon increasing [Na+]o from 0 to 25 mM, indicate that Na+/H+ exchange is active at pHi 7.4. Intracellular H+ stimulated apical Na+ entry by titration of more than one site (apparent pK 7.1, Hill coefficient 1.7). The results suggest that external Na+ and H+ interact with one site of the Na+/H+ exchanger and that cytoplasmic H+ acts on at least two sites. The external titratable group seems to be an imidazolium, which is apparently different from the amiloride-binding site. The dependence of Na+ entry on pHi supports the notion that the Na+/H+ exchanger is operational under normal transport conditions.