Simultaneous detection of cell volume and intracellular pH in isolated rat duodenal cells by confocal microscopy and BCECF

Facile, rapid one-pot synthesis of multifunctional gold nanoclusters for cell imaging, hydrogen sulfide detection and pH sensing

In this study, we have developed a facile, rapid one-pot strategy for synthesis of orange fluorescent gold nanoclusters (MBISA-AuNCs) at room temperature by using 2-Mercapto-5-benzimidazolesulfonic acid (MBISA) as both reducing and protecting reagent. The prepared AuNCs exhibited prominent advantages including high fluorescent quantum yield, good water solubility, excellent biocompatibility and low toxicity. Based on these superior properties, the AuNCs have been multi-talented applied in cell imaging, hydrogen sulfide detection and pH sensing. Confocal fluorescence imaging showed that the MBISA-AuNCs could enter living cells and distribute in the cytoplasm. Additionally, the obtained AuNCs could visualize H₂S fluctuations in living cells without interference of autofluorescence based on their high sensitivity and selectivity detection for H₂S with a linear range of 2.7 × 10^-11-8.5 × 10^-4 M and a detection limit of 0.024 nM. Most strikingly, the AuNCs exhibited strong pH dependent behavior and responded linearly, rapidly and reversibly to minor pH fluctuations within the range of 2.01-12.00. Therefore, the AuNCs could also image pH fluctuations in live cells with negligible autofluorescence and provided a new method of analysis to visualize monitoring wide pH range change in live cells.

An aminoquinoline based biocompatible fluorescent and colourimetric pH sensor designed for cancer cell discrimination

A simple, low cost aminoquinoline based pH sensor,HLwas prepared and it works at a low pH range.HLexhibits cell permeability and used as an effective tool for differentiating between normal and cancer cells.

Ultra sensitive and wide-range pH sensor based on the BSA-capped Cu nanoclusters fabricated by fast synthesis through the use of hydrogen peroxide additive

This study reports a new pH sensor based on BSA-capped copper nanoclusters. The proposed pH sensor provides better sensitivity and a wider ranging pH response compared with other metal nanoclusters reported in the literature.

A general quantitative pH sensor developed with dicyandiamide N-doped high quantum yield graphene quantum dots

A general quantitative pH sensor for environmental and intracellular applications was developed by the facile hydrothermal preparation of dicyandiamide (DCD) N-doped high quantum yield (QY) graphene quantum dots (GQDs) using citric acid (CA) as the carbon source. The obtained N-doped GQDs have excellent photoluminesence (PL) properties with a relatively high QY of 36.5%, suggesting that N-doped chemistry could promote the QY of carbon nanomaterials. The possible mechanism for the formation of the GQDs involves the CA self-assembling into a nanosheet structure through intermolecular H-bonding at the initial stage of the reaction, and then the pure graphene core with many function groups formed through the dehydration between the carboxyl and hydroxyl of the intermolecules under hydrothermal conditions. These N-doped GQDs have low toxicity, and are photostable and pH-sensitive between 1.81 to 8.96, giving a general pH sensor with a wide range of applications from real water to intracellular contents.

Fluorescent pH sensor based on Ag@SiO2 core-shell nanoparticle

We have demonstrated a novel method for the preparation of a fluorescence-based pH sensor by combining the plasmon resonance band of Ag core and pH sensitive dye (HPTS). A thickness-variable silica shell is placed between Ag core and HPTS dye to achieve the maximum fluorescence enhancement. At the shell thickness of 8 nm, the fluorescence intensity increases 4 and 9 times when the sensor is excited at 405 and 455 nm, respectively. At the same time, the fluorescence intensity shows a good sensitivity toward pH value in the range of 5-9, and the ratio of emission intensity at 513 nm excited at 455 nm to that excited at 405 nm versus the pH value in the range of 5-9 is determined. It is believed that the present pH sensor has the potential for determining pH real time in the biological sample.

Functional interaction between AQP2 and TRPV4 in renal cells

We have previously demonstrated that renal cortical collecting duct cells (RCCD(1)), responded to hypotonic stress with a rapid activation of regulatory volume decrease (RVD) mechanisms. This process requires the presence of the water channel AQP2 and calcium influx, opening the question about the molecular identity of this calcium entry path. Since the calcium permeable nonselective cation channel TRPV4 plays a crucial role in the response to mechanical and osmotic perturbations in a wide range of cell types, the aim of this work was to test the hypothesis that the increase in intracellular calcium concentration and the subsequent rapid RVD, only observed in the presence of AQP2, could be due to a specific activation of TRPV4. We evaluated the expression and function of TRPV4 channels and their contribution to RVD in WT-RCCD(1) (not expressing aquaporins) and in AQP2-RCCD(1) (transfected with AQP2) cells. Our results demonstrated that both cell lines endogenously express functional TRPV4, however, a large activation of the channel by hypotonicity only occurs in cells that express AQP2. Blocking of TRPV4 by ruthenium red abolished calcium influx as well as RVD, identifying TRPV4 as a necessary component in volume regulation. Even more, this process is dependent on the translocation of TRPV4 to the plasma membrane. Our data provide evidence of a novel association between TRPV4 and AQP2 that is involved in the activation of TRPV4 by hypotonicity and regulation of cellular response to the osmotic stress, suggesting that both proteins are assembled in a signaling complex that responds to anisosmotic conditions.

A microfluidic chip for real-time studies of the volume of single cells

We report a microfluidic chip that is capable of measuring volume changes in single cells in real-time. Single eukaryotic cells were immobilized in the sensing area and changes in volume in response to hypotonic challenges and drugs were measured using the electrical impedance method. Experiments on MDCK cells showed that the maximum swelling and the time course of swelling vary between individual cells following hypotonic stimulation. The microfluidic chip allows, rapid and convenient change of solutions, enabling detailed studies of various drugs and chemicals that may play important role in cell physiology at the single cell level.

Role of AQP2 in activation of calcium entry by hypotonicity: implications in cell volume regulation

We previously reported in a rat cortical collecting duct cell line (RCCD1) that the presence of aquaporin 2 (AQP2) in the cell membrane is critical for the rapid activation of regulatory volume decrease mechanisms (RVD) (Ford et al. Biol Cell 97: 687–697, 2005). The aim of our present work was to investigate the signaling pathway that links AQP2 to this rapid RVD activation. Since it has been previously described that hypotonic conditions induce intracellular calcium ([Ca2+]i) increases in different cell types, we tested the hypothesis that AQP2 could have a role in activation of calcium entry by hypotonicity and its implication in cell volume regulation. Using a fluorescent probe technique, we studied [Ca2+]iand cell volume changes in response to a hypotonic shock in WT-RCCD1(not expressing aquaporins) and in AQP2-RCCD1(transfected with AQP2) cells. We found that after a hypotonic shock only AQP2-RCCD1cells exhibit a substantial increase in [Ca2+]i. This [Ca2+]iincrease is strongly dependent on extracellular Ca2+and is partially inhibited by thapsigargin (1 μM) indicating that the rise in [Ca2+]ireflects both influx from the extracellular medium and release from intracellular stores. Exposure of AQP2-RCCD1cells to 100 μM gadolinium reduced the increase in [Ca2+]isuggesting the involvement of a mechanosensitive calcium channel. Furthermore, exposure of cells to all of the above described conditions impaired rapid RVD. We conclude that the expression of AQP2 in the cell membrane is critical to produce the increase in [Ca2+]iwhich is necessary to activate RVD in RCCD1cells.

The duodenal mucosal bicarbonate secretion

The duodenal lumen is exposed to aggressive factors with a high potential to cause damage to the mucosa. Bicarbonate secretion by the duodenal mucosa is accepted as the primary important defense mechanism against the hydrochloric acid intermittently expelled from the stomach. The present work concerns both the influence of the central nervous system and the effects of the hormone melatonin on duodenal bicarbonate secretion in anesthetized rats in vivo as well as effects of melatonin on intracellular calcium signaling by duodenal enterocyte in vitro examined in tissues of both human and rat origin. The main findings were as follows: Melatonin is a potent stimulant of duodenal mucosal bicarbonate secretion and also seems to be involved in the acid-induced stimulation of the secretion. Stimulation elicited in the central nervous system by the alpha1-adrenoceptor agonist phenylephrine induced release of melatonin from the intestinal mucosa and a four-fold increase in alkaline secretion. The melatonin antagonist luzindole abolished the duodenal secretory response to administered melatonin and to central nervous phenylephrine but did not influence the release of intestinal melatonin. Central nervous stimulation was also abolished by synchronous ligation of the vagal trunks and the sympathetic chains at the sub-laryngeal level. Melatonin induced release of calcium from intracellular stores and also influx of extracellular calcium in isolated duodenal enterocytes. Enterocytes in clusters functioned as a syncytium. Overnight fasting rapidly and profoundly down-regulated the responses to the duodenal secretagogue orexin-A and the muscarinic agonist bethanechol but not those to melatonin or vasoactive intestinal polypeptide.

Melatonin-induced calcium signaling in clusters of human and rat duodenal enterocytes

The amount of melatonin present in enterochromaffin cells in the alimentary tract is much higher than that in the central nervous system, and melatonin acting at MT(2) receptors mediates neural stimulation of mucosal HCO(3)(-) secretion in duodenum in vivo. We have examined effects of melatonin and receptor ligands on intracellular free calcium concentration ([Ca(2+)](i)) signaling in human and rat duodenal enterocytes. Clusters of interconnecting enterocytes (10-50 cells) were isolated by mild digestion (collagenase/dispase) of human duodenal biopsies or rat duodenal mucosa loaded with fura-2 AM and attached to the bottom of a temperature-controlled perfusion chamber. Clusters provided viable preparations and respond to stimuli as a syncytium. Melatonin and melatonin receptor agonists 2-iodo-N-butanoyl-5-methoxytryptamine and 2-iodomelatonin (1.0-100 nM) increased enterocyte [Ca(2+)](i), EC(50) of melatonin being 17.0 +/- 2.6 nM. The MT(2) receptor antagonists luzindole and N-pentanoyl-2-benzyltryptamine abolished the [Ca(2+)](i) responses. The muscarinic antagonist atropine (1.0 microM) was without effect on basal [Ca(2+)](i) and did not affect the response to melatonin. In the main type of response, [Ca(2+)](i) spiked rapidly and returned to basal values within 4-6 min. In another type, the initial rise in [Ca(2+)](i) was followed by rhythmic oscillations of high amplitude. Melatonin-induced enterocyte [Ca(2+)](i) signaling as well as mucosal cell-to-cell communication may be involved in stimulation of duodenal mucosal HCO(3)(-) secretion.

NHE1, NHE2, and NHE3 contribute to regulation of intracellular pH in murine duodenal epithelial cells

Na(+)/H(+)-exchangers (NHE) mediate acid extrusion from duodenal epithelial cells, but the isoforms involved have not previously been determined. Thus we investigated 1) the contribution of Na(+)-dependent processes to acid extrusion, 2) sensitivity to Na(+)/H(+) exchange inhibitors, and 3) molecular expression of NHE isoforms. By fluorescence spectroscopy the recovery of intracellular pH (pH(i)) was measured on suspensions of isolated acidified murine duodenal epithelial cells loaded with 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Expression of NHE isoforms was studied by RT-PCR and Western blot analysis. Reduction of extracellular Na(+) concentration ([Na(+)](o)) during pH(i) recovery decreased H(+) efflux to minimally 12.5% of control with a relatively high apparent Michaelis constant for extracellular Na(+). The Na(+)/H(+) exchange inhibitors ethylisopropylamiloride and amiloride inhibited H(+) efflux maximally by 57 and 80%, respectively. NHE1, NHE2, and NHE3 were expressed at the mRNA level (RT-PCR) as well as at the protein level (Western blot analysis). On the basis of the effects of low [Na(+)](o) and inhibitors we propose that acid extrusion in duodenal epithelial cells involves Na(+)/H(+) exchange by isoforms NHE1, NHE2, and NHE3.