Relationship between intracellular pH (pHi) and calcium (Cai2+) in avian heart fibroblasts

Fluid Shear Stress Effects on Endothelial Cell Cytosolic pH

Fluid flow can modulate endothelial cell intracellular pH (pH(i)). Venous and arterial shear stresses of 1.4 and 14 dyn/cm2, respectively, induced intracellular acidification. The kinetics of the process and magnitude of acidification were dependent on the level of shear stress. Endothelial cells exposed to a venous shear stress were able to recover from the acidification, whereas cells exposed to an arterial shear stress remained acidic. Addition of SITS (1 mM), a HCO(3) (-)/CI(-) exchange inhibitor, greatly reduced the shear stress induced acidification, suggesting that the HCO(3) (-)/C1(-) exchanger is activated by shear stress. Shear stress may activate the exchanger by lowering the [HCO(3) (-)] at the cell surface via convective mass transfer. Altering the HCO(3) (-) gradient across the cell membrane activates the exchanger and, as a consequence, results in intracellular acidification. Perfusion with media containing ATP (10 microM) altered the kinetics of flow-induced acidification observed at both shear stress levels. ATP modulation of pH(i) may be coupled to the rise in [Ca(2+)](j) known to occur with ATP stimulation. To summarize, media perfusion induces intracellular acidification in endothelial cells, and there is evidence to suggest that pH(i) may serve as a second messenger to modulate flow associated changes in endothelial cell metabolism.

Role of Membrane Components in Thermal Injury of Cells and Development of Thermotolerance

Exposure of cells to hyperthermia induces a transient resistance to subsequent heat treatment. The specific mechanisms responsible for hyperthermic cell killing and thermotolerance development are not well understood. It seems that heat may induce at least two different states of thermotolerance, of which one is dependent on protein synthesis. The expression of thermotolerance may include multiple cytoplasmic and membrane components. A number of studies have indicated that membranes play an important role in governing the thermal injury of cells. It seems, therefore, that heat denatured plasma membrane proteins may be a potential target for thermal stress and a trigger for the induction of thermotolerance. The localization of heat shock proteins in the plasma membrane and the suggestion of thermal resistance in enucleate erythrocytes support this suggestion. However, a direct relationship between the plasma membrane and hyperthermic killing or development of thermotolerance has not been found.

Interdependence of Ca2+ and proton movements in trout hepatocytes

This study was undertaken to investigate possible interrelationships between Ca2+ homeostasis and pH regulation in trout hepatocytes. Exposure of cells to Ca2+ mobilizing agents ionomycin (0.5 μmol l–1) and thapsigargin (0.1 μmol l–1)induced an increase in intracellular pH (pHi) that was dependent on Ca2+ influx from the extracellular medium as well as Ca2+ release from intracellular pools. Surprisingly, this increase in pHi and intracellular Ca2+ concentration,[Ca2+]i, was not accompanied by any change in proton secretion. By contrast, removal of extracellular Ca2+(Ca2+e) using EGTA (0.5 mmol l–1)briefly increased proton secretion rate with no apparent effect on pHi, while chelation of Ca2+i using BAPTA-AM (25 μmol l–1) resulted in a drop in pHi and a sustained increase in proton secretion rate. [Ca2+]i therefore affected intracellular proton distribution and/or proton production and also affected the distribution of protons across the cell membrane. Accordingly, changes in pHi were not always compensated for by proton secretion across the cell membrane.

Alteration in pHe below and above normal values induced a slow,continuous increase in [Ca2+]i with a tendency to stabilize upon exposure to high pHe values. Rapid pHi increase induced by NH4Cl was accompanied by an elevation in[Ca2+]i from both extracellular and intracellular compartments. Ca2+e appeared to be involved in pHi regulation following NH4Cl-induced alkalinization whereas neither removal of Ca2+e nor chelation of Ca2+i affected pHi recovery following Na-propionate exposure. Similarly, [Ca2+]i increase induced by hypertonicity appeared to be a consequence of the changes in pHi as Na-free medium as well as cariporide diminished the hypertonicity-induced increase in[Ca2+]i. These results imply that a compensatory relationship between changes in pHi and proton secretion across cell plasma membrane is not always present. Consequently, calculating proton extrusion from buffering capacity and rate of pHi change cannot be taken as an absolute alternative for measuring proton secretion rate, at least in response to Ca2+ mobilizing agents.

Hypoxia-induced increase in intracellular calcium concentration in endothelial cells: role of the Na(+)-glucose cotransporter

Hypoxia is a common denominator of many vascular disorders, especially those associated with ischemia. To study the effect of oxygen depletion on endothelium, we developed an in vitro model of hypoxia on human umbilical vein endothelial cells (HUVEC). Hypoxia strongly activates HUVEC, which then synthesize large amounts of prostaglandins and platelet-activating factor. The first step of this activation is a decrease in ATP content of the cells, followed by an increase in the cytosolic calcium concentration ([Ca(2+)](i)) which then activates the phospholipase A(2) (PLA(2)). The link between the decrease in ATP and the increase in [Ca(2+)](i) was not known and is investigated in this work. We first showed that the presence of extracellular Na(+) was necessary to observe the hypoxia-induced increase in [Ca(2+)](i) and the activation of PLA(2). This increase was not due to the release of Ca(2+) from intracellular stores, since thapsigargin did not inhibit this process. The Na(+)/Ca(2+) exchanger was involved since dichlorobenzamil inhibited the [Ca(2+)](i) and the PLA(2) activation. The glycolysis was activated, but the intracellular pH (pH(i)) in hypoxic cells did not differ from control cells. Finally, the hypoxia-induced increase in [Ca(2+)](i) and PLA(2) activation were inhibited by phlorizin, an inhibitor of the Na(+)-glucose cotransport. The proposed biochemical mechanism occurring under hypoxia is the following: glycolysis is first activated due to a requirement for ATP, leading to an influx of Na(+) through the activated Na(+)-glucose cotransport followed by the activation of the Na(+)/Ca(2+) exchanger, resulting in a net influx of Ca(2+).

[Ca2+]i as a potential downregulator of alpha2beta1-integrin-mediated A2058 tumor cell migration to type IV collagen

We have investigated cellular Ca2+ regulation during A2058 human melanoma cell chemotaxis to type IV collagen (CIV). We have identified alpha2beta1-integrin as the primary mediator of A2058 cell response to CIV in vitro. Integrin ligation initiated a characteristic intracellular Ca2+ concentration ([Ca2+]i) response consisting of an internal release and a receptor-mediated Ca2+ entry. Thapsigargin (TG) pretreatment drained overlapping and CIV-inducible internal Ca2+ stores while initiating a store-operated Ca2+ release (SOCR). CIV-mediated Ca2+ entry was additive to TG-SOCR, suggesting an independent signaling mechanism. Similarly, ionophore application in a basal medium containing Ca2+ initiated a sustained influx. Elevated [Ca2+]i from TG-SOCR or ionophore significantly attenuated cell migration to CIV by recruiting the Ca2+/calcineurin-mediated signaling pathway. Furthermore, low [Ca2+]i induced by EGTA application in the presence of ionophore fully restored cell motility to CIV. Together, these results suggest that [Ca2+]i signaling accompanying A2058 cell response to alpha2beta1-integrin ligation is neither necessary nor sufficient and that elevated [Ca2+]i downregulates cell motility via a calcineurin-mediated mechanism in A2058 cell chemotaxis to CIV.

Acid stimulates E-cadherin surface expression on gastric epithelial cells to stabilize barrier functions via influx of calcium

BACKGROUND AND AIMS

E-cadherin, which is a [Ca2+]-dependent, homotypic cell-cell adhesion molecule, is expressed in gastrointestinal epithelial cells. Much has been learned about the down-regulation of E-cadherin expression in gastrointestinal tumours, Barrett's oesophageal dysplasia, and Crohn's disease, but the functions of this molecule in normal gastrointestinal mucosa are less known.

METHODS

In this study, we investigated the relationship between E-cadherin expression and permeability using rat cultured gastric and intestinal epithelial cells following a 30-min exposure to various pH solutions. We also investigated the participation of [Ca2+] in these events.

RESULTS

E-cadherin expression increased under acid (pH 4) but not alkali (pH 10 or 11) exposure only for gastric epithelial cells. Gastric epithelial permeability was maintained only against acid exposure while intestinal permeability increased under both conditions. Transient influx of [Ca2+] was only observed for gastric epithelial cells just after acid exposure.

CONCLUSIONS

These findings suggest that E-cadherin expression on gastric epithelium stabilizes the epithelial barrier against acid, probably through influx of [Ca2+]. This event is thought to be one of the protective mechanisms in gastric mucosa against acid back-diffusion, which is one of the causes of peptic ulcer formation.

Phosphorylation-dependent stimulation of prostanoid synthesis by nigericin in cerebral endothelial cells

Nigericin decreases intracellular pH (pH(i)) and stimulates prostanoid (PG) synthesis in endothelial cells from cerebral microvessels of newborn pigs. Nigericin-induced PG production was abolished by protein tyrosine kinase (PTK) inhibitors and amplified by phorbol 12-myristate 13-acetate (PMA) or protein tyrosine phosphatase (PTP) inhibitors. Nigericin-induced PG production in PMA-primed cells was potentiated by PTP inhibitors and abrogated by PTK inhibitors. Phospholipase A(2) (PLA(2)) activity was stimulated by nigericin in a phosphorylation-dependent manner. Nigericin's effects on PG production and PLA(2) activity were reproduced by ionomycin, which activates cytosolic PLA(2) (cPLA(2)). cPLA(2) was immunodetected in endothelial cell lysates. We found no evidence that nigericin's effects are mediated via mitogen-activated protein (MAP) kinase [extracellularly regulated kinase 1 (ERK1) and ERK2] activation: although nigericin stimulated detergent-soluble MAP kinase, its effects were not amplified by PMA or PTP inhibitors. Phosphorylation-dependent stimulation of PG synthesis was also observed when pH(i) was decreased by sodium propionate or a high level of CO(2). Altogether, our data indicate that nigericin and decreased pH(i) stimulate PG synthesis by a protein phosphorylation-dependent mechanism involving cross talk between pathways mediated by PTK and PTP and by protein kinase C; cPLA(2) appears to be a key enzyme affected by nigericin and decreased pH(i).

Effect of intracellular Ca2+ chelation with the acetoxymethyl ester-derived form of bis(o-aminophenoxy)ethane-N,N,N,N',N'-tetraacetic acid on meiotic division and chromosomal segregation in mouse oocytes

PURPOSE

Our purpose was to ascertain the effect of intracellular Ca2+ chelation on the chromosomal distribution and segregation of mouse oocytes during maturation in vitro.

METHODS

Germinal vesicle oocytes were loaded with the acetoxymethyl ester-derived form of bis(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM). Chromosomal distribution and segregation of control and BAPTA-AM-treated metaphase II (MII) oocytes were evaluated at 16 hr, and intracellular ATP content at 0, 1, and 16 hr after BAPTA-AM loading.

RESULTS

BAPTA-AM treatment decreased (P < or = 0.05) the potential for in vitro maturation, increased (P < or = 0.0001) the percentage of oocytes displaying an abnormal distribution of metaphase II chromosomes in the meiosis II spindle and aneuploidy, and decreased (P < or = 0.005) the ATP content at 0, 1, and 16 hr of culture compared to the control groups.

CONCLUSIONS

These findings raise some concern about any other condition/drug that may directly or indirectly decrease the intracellular Ca2+ concentration in human oocytes.

Properties of a novel pH-dependent Ca2+ permeation pathway present in male germ cells with possible roles in spermatogenesis and mature sperm function

Rises of intracellular Ca2+ ([Ca2+]i) are key signals for cell division, differentiation, and maturation. Similarly, they are likely to be important for the unique processes of meiosis and spermatogenesis, carried out exclusively by male germ cells. In addition, elevations of [Ca2+]i and intracellular pH (pHi) in mature sperm trigger at least two events obligatory for fertilization: capacitation and acrosome reaction. Evidence implicates the activity of Ca2+ channels modulated by pHi in the origin of these Ca2+ elevations, but their nature remains unexplored, in part because work in individual spermatozoa are hampered by formidable experimental difficulties. Recently, late spermatogenic cells have emerged as a model system for studying aspects relevant for sperm physiology, such as plasmalemmal ion fluxes. Here we describe the first study on the influence of controlled intracellular alkalinization on [Ca2+]i on identified spermatogenic cells from mouse adult testes. In BCECF [(2',7')-bis(carboxymethyl)- (5, 6)-carboxyfluorescein]-AM-loaded spermatogenic cells, a brief (30-60 s) application of 25 mM NH4Cl increased pHi by approximately 1.3 U from a resting pHi approximately 6.65. A steady pHi plateau was maintained during NH4Cl application, with little or no rebound acidification. In fura-2-AM-loaded cells, alkalinization induced a biphasic response composed of an initial [Ca2+]i drop followed by a two- to threefold rise. Maneuvers that inhibit either Ca2+ influx or intracellular Ca2+ release demonstrated that the majority of the Ca2+ rise results from plasma membrane Ca2+ influx, although a small component likely to result from intracellular Ca2+ release was occasionally observed. Ca2+ transients potentiated with repeated NH4Cl applications, gradually obliterating the initial [Ca2+]i drop. The pH-sensitive Ca2+ permeation pathway allows the passage of other divalents (Sr2+, Ba2+, and Mn2+) and is blocked by inorganic Ca2+ channel blockers (Ni2+ and Cd2+), but not by the organic blocker nifedipine. The magnitude of these Ca2+ transients increased as maturation advanced, with the largest responses being recorded in testicular sperm. By extrapolation, these findings suggest that the pH-dependent Ca2+ influx pathway could play significant roles in mature sperm physiology. Its pharmacology and ion selectivity suggests that it corresponds to an ion channel different from the voltage-gated T-type Ca2+ channel also present in spermatogenic cells. We postulate that the Ca2+ permeation pathway regulated by pHi, if present in mature sperm, may be responsible for the dihydropyridine-insensitive Ca2+ influx required for initiating the acrosome reaction and perhaps other important sperm functions.

pH regulation in horizontal cells of the skate retina

To examine the mechanisms by which horizontal cells regulate intracellular pH (pHi), measurements were recorded from isolated cells enzymatically dissociated from the skate retina utilizing the pH-sensitive dye BCECF. In a HCO3--containing Ringer solution, steady-state pHi was 7.32+/-0.13 (mean+/-S.D., n=70). Recovery from acidification was examined using the NH4+ prepulse technique. When NH4+ was removed from the extracellular solution, pHi dropped rapidly to approximately 0.3 pH units below the initial baseline, and then recovered at an initial rate of approximately 0.072 pH units/min. During recovery of pHi after the acid load, the removal of Na+ or the addition of amiloride from a HCO3--free extracellular solution reduced the rate of recovery by 79%+/-11% and 69%+/-14%, respectively. In the presence of DIDS, which inhibits primarily anion transport, or during the removal of Na+, the recovery from acidification was reduced by 83%+/-10% and 70%+/-11%, respectively, as compared to the control value in HCO3--containing solution. These results suggest that the skate horizontal cell possesses a Na/H exchanger as well as a Na+-and HCO3--dependent mechanism for removal of excess acid. Removal of HCO3- or Cl- from the extracellular solution had little effect on pHi, but removing external Na+ induced a marked decrease in pHi that fell at an initial rate of approximately 0.3 pH units min-1. This rate of acidification was decreased by 58%+/-19% in the presence of DIDS (500 micron) and reduced by 28%+/-13% with the addition of amiloride (2 mm). Thus, Na- and HCO3-dependent transport was about 2-fold more active than Na/H exchange during low Na+-induced acidification. The intrinsic pH-buffer capacity, determined from the pHi change induced by incremental reductions in the [NH4+] of the extracellular solution, was 24.2 mm/pH unit at the horizontal cell's resting pHi. Moreover, pHi was relatively insensitive to changes in membrane potential; in experiments under whole-cell voltage clamp (-70 mV), intracellular pH remained constant during depolarizing voltage swings to -30 mV or +30 mV, as well as during hyperpolarizing pulses to -90 or -110 mV.

Cell Signaling and Heat Shock Protein Expression

Exposure of cells and organs to heat shock is associated with numerous changes in various cellular metabolic parameters and overexpression of proteins collectively known as heat shock proteins (HSP). In this communication we review the cell-signaling events that are altered in response to heat shock as they relate to the subsequent induction of HSP 70 kd (HSP-70) expression. We also review the mechanisms by which HSP-70 is involved in conferring cytoprotective effects. The possibility of altering HSP expression through manipulations of the cell-signal process has clinical importance. Copyright 1996 S. Karger AG, Basel

Hyperosmotic modulation of the cytosolic calcium concentration in a rat osteoblast-like cell line

1. The effects of hyperosmotic stress on cytosolic calcium concentration ([Ca2+]i) were studied by ratio image analysis in single cells of an osteoblast-like bone cell line (RCJ 1.20) loaded with fura-2 AM. 2. The ratio (340 nm/380 nm) of steady-state [Ca2+]i in resting osteoblasts kept in Hepes-buffered medium was 0.82 +/- 0.04. A hyperosmotic stimulus (200 mosmol l-1 sucrose) produced a [Ca2+]i transient with a peak ratio of 1.28 +/- 0.09, which decayed with an apparent half-life (t1/2) of 42.7 +/- 2.6 s. 3. The hyperosmotically induced [Ca2+]i transients were insensitive to verapamil, diltiazem or nifedipine, which excludes the involvement of dihydropyridine-sensitive Ca2+ channels in the process. Non-specific Ca2+ channel blockers (Mn2+, Ni2+, La3+ or Gd3+) partially abolished the hyperosmotically induced [Ca2+]i elevation, indicating the contribution of extracellular Ca2+ influx. 4. A hyperosmotic stimulus applied in Ca(2+)-free medium (0.5 mM EGTA) lowered the [Ca2+]i peak to a ratio of 0.96 +/- 0.08 (P < 0.001) compared with a Ca(2+)-containing medium. This suggests that the [Ca2+]i increase is due to extracellular influx, as well as release from an intracellular Ca2+ pool. 5. Application of thapsigargin (0.5 microM), a specific inhibitor of endoplasmic reticulum Ca(2+)-ATPase, in Ca(2+)-free medium caused transient [Ca2+]i elevation to peak ratios of 1.33 +/- 0.09, and completely abolished the [Ca2+]i response to a hyperosmotic stimulus. This implies the existence of a thapsigargin-sensitive intracellular pool of Ca2+ that is mobilized by hyperosmotic stimulus.(ABSTRACT TRUNCATED AT 250 WORDS)

Receptor-operated Ca2+ signaling and crosstalk in stimulus secretion coupling

In the cells of higher eukaryotic organisms, there are several messenger pathways of intracellular signal transduction, such as the inositol 1,4,5-trisphosphate/Ca2+ signal, voltage-dependent and -independent Ca2+ channels, adenylate cyclase/cyclic adenosine 3',5'-monophosphate, guanylate cyclase/cyclic guanosine 3',5'-monophosphate, diacylglycerol/protein kinase C, and growth factors/tyrosine kinase/tyrosine phosphatase. These pathways are present in different cell types and impinge on each other for the modulation of the cell function. Ca2+ is one of the most ubiquitous intracellular messengers mediating transcellular communication in a wide variety of cell types. Over the last decades it has become clear that the activation of many types of cells is accompanied by an increase in cytosolic free Ca2+ concentration ([Ca2+]i) that is thought to play an important part in the sequence of events occurring during cell activation. The Ca2+ signal can be divided into two categories: receptor- and voltage-operated Ca2+ signal. This review describes and integrates some recent views of receptor-operated Ca2+ signaling and crosstalk in the context of stimulus-secretion coupling.

Effect of low extracellular Ca2+ on growth, spreading area, cytoplasmic Ca2+ concentration, and intracellular pH in normal and transformed human fibroblasts

The transformation of certain cells reduces the requirement of extracellular Ca2+ for growth. The SV-40 transformed human lung fibroblasts, WI-38 VA13, require less Ca2+ than normal WI-38 cells. Spreading area of the normal cells decreases when cultured in 10 microM Ca2+ medium. Intracellular calcium concentration ([Ca2+]i) of the normal and transformed cells cultured in 10 microM and 2 mM Ca2+ media was measured by the fluorescence microscope technique using fura-2 as a probe. The [Ca2+]i is measured in the resting state and during mobilization by serum or bradykinin stimulation. The lowering of extracellular calcium concentration results in a decrease in the resting state [Ca2+]i of both normal and transformed cells. Although the total decrease in [Ca2+]i is the same for both cells, the rate of decrease is much faster in normal cells than in transformed cells. Low extracellular Ca2+ reduces the number of cells responsive to the serum or bradykinin stimulation and decreases the peak [Ca2+]i value in both cells. In addition, we investigated, using BCECF as a fluorescent probe, the intracellular pH (pHi) of normal and transformed cells maintained at low and normal Ca2+. The low Ca2+ condition makes pHi acidic in normal cells but not in transformed cells. The acidification of the normal cell is accompanied by a decrease in the spreading area of the cells. The decrease of the cell attachment, followed by the reduced spreading area, induces the acidic pHi. These results suggest that the reduced Ca2+ requirement of transformed cells for growth is related to the mechanism of pHi regulation rather than Ca2+ homeostasis and, possibly, to the anchorage-independent growth, which is a unique feature of transformed cells.

Effects of ammonium chloride on membrane currents of acinar cells dispersed from the rat parotid gland

In acinar cells freshly dispersed from rat parotid glands, the effects of ammonium chloride (NH4Cl) on membrane currents were studied using the whole-cell clamp method. When membrane currents were recorded with command pulses to 0 mV, applied at 2-s intervals from a holding potential of -70 mV, NH4Cl (5-20 mM) transiently decreased outward currents and then slowly increased both outward and inward currents. After reaching a peak in about 40-50 s, both outward and inward currents gradually decreased in the presence of NH4Cl and, on its wash-out, the currents returned to the control level. Butyrate (5-20 mM) had little effect on the resting membrane currents, but markedly inhibited the response to NH4Cl. Tetraethylammonium (5 mM) strongly reduced both the resting and NH4Cl-induced outward currents, whereas it slightly potentiated the NH4Cl-induced inward current without affecting the membrane current at the holding potential. Without ATP in the patch pipettes, carbachol-induced membrane currents were relatively resistant to Ca2+ removal from the external medium, but NH4Cl-induced currents were quickly abolished in the absence of Ca2+. We conclude that intracellular alkalinization with NH4Cl increases Ca2+ influx and activates Ca(2+)-dependent outward K+ and inward Cl- currents.

Relationship between intracellular pH changes, activation of protein kinase C and NADPH oxidase in macrophages

Activation of the superoxide-generating NADPH oxidase by phorbol ester or zymosan induced a cytoplasmic acidification when liver macrophages were incubated in sodium-free media or in the presence of amiloride. Staurosporine or desensitization of protein kinase C inhibited phorbol ester- and zymosan-induced pH changes and generation of superoxide. The intracellular pH remained unchanged in cells incubated in physiological sodium media. Ionomycin and arachidonic acid did not induce a change in intracellular pH or a generation of superoxide. Fluoride, which has been shown to induce a translocation of protein kinase C in these cells, did not elicit superoxide generation but induced a decrease in intracellular pH. These experiments support (1) a role of the Na+/H+ antiporter in macrophages as a metabolic regulator of intracellular pH upon stimulation of the superoxide-generating NADPH oxidase, and (2) suggest an involvement of protein kinase C in this process.

Microspectrofluorometry as a tool for investigation of non-calcium interactions of Indo-1

Indo-1 is a fluorescent calcium probe used to measure intracellular free calcium concentrations. These measurements are often performed by comparing the fluorescence intensities of Indo-1-treated cells at two selected wavelengths corresponding to the maxima of the fluorescence spectra of the calcium-bound and calcium-free forms. In this study, we used an optical multichannel analyser to numerise the fluorescence emitted by a single cell. A computerised resolution of numerised spectra was used on intracellular Indo-1 fluorescence. Calculation of numerical and graphic estimators allows us to evaluate the fit of the resolution. Different sets of characteristic spectra were compared using this method. It appeared that no linear combination of the two known forms of Indo-1 and of the cell autofluorescence can fit with spectra of Indo-1-treated cells. In addition, a study of the physico-chemical properties of Indo-1 shows the existence of two other forms of the molecule: a protonated form (maximum emission at 455 nm) and a form in interaction with proteins (maximum emission at 438 nm). Taking into account the contribution of these two new forms leads to an improved spectral resolution of the fluorescence of Indo-1-treated living cells and, therefore, improves calcium measurements. Moreover, quantification of the amount of the protonated form of Indo-1 allows a measurement of intracellular pH at the same time as calcium determination.

Effect of intracellular pH on cytosolic free [Ca2+] in human epidermoid A-431 cells

This study characterizes the correlation between intracellular pH (pHi) and the cytosolic free Ca2+ concentration ([Ca2+]i) in suspended and adherent human epidermoid A-431 cells. Using the fluorescent dyes 2,7-bis(carboxyethyl)carboxyfluorescein acetoxymethyl ester (BCECF) and fura-2, the resting pHi and [Ca2+]i in suspended cells were 7.23 +/- 0.03 and 209 +/- 30 nM; those in adherent cells were 7.28 +/- 0.02 and 87 +/- 5 nM. Removal of external Ca2+ did not change the resting pHi but reduced the resting [Ca2+]i, indicating the resting level of [Ca2+]i is in part maintained by an influx of Ca2+ from the external medium. When both suspended and adherent cells were acidified or alkalinized, resting [Ca2+]i was altered. An intracellular acidification induced a fall in [Ca2+]i, and a rise in pHi induced a rise in [Ca2+]i. These changes in [Ca2+]i were correlated with an uptake of 45Ca2+ from the external medium, whereas no Ca2+ efflux occurred. The alteration in [Ca2+]i induced by modification of pHi was abolished in the absence of external Ca2+ or by adding 2 mM CoCl2, LaCl3, and attenuated by the addition of 2 mM MnCl2 to the bathing medium. It was insensitive to the voltage-gated Ca2+ channel blockers nifedipine or verapamil (1 mM). CoCl2, LaCl3, and MnCl2 each induced changes in pHi and [Ca2+]i but verapamil and nifedipine did not. Because CoCl2, LaCl3, and MnCl2 are also known to block Na+/Ca2+ exchange, intracellular Na+ ([Na+]i) was measured by flame photometry in acidified or alkalinized cells. In either case no change in [Na+]i was observed. Furthermore, treatment with amiloride (100 microM), a blocker of the Na+/Ca2+ exchanger, did not inhibit the pH-induced changes in [Ca2+]i. 1,2-bis(o-Aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) (100 microM), a Ca2+ chelator, induced a decrease in pHi as well as a reduction of [Ca2+]i, also supporting the direct relation between pHi and [Ca2+]i. 3,4,5-Trimethoxybenzoic acid 8-(diethylamino)ocytl ester HCl (TMB-8) (100 microM), a known blocker of intracellular Ca2+ mobilization, did not change the resting pHi and [Ca2+]i in normal cells or cells acidified or alkalinized. This observation, taken together with data from cells incubated in the absence of external Ca2+, suggests intracellular Ca2+ pools are not involved in changes in [Ca2+]i that result from a modification of pHi. Resting pHi and [Ca2+]i in cells treated with either 8-bromo-dibutyryl cAMP (1 mM) or forskolin (150 microM) are not changed.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of pH on intracellular calcium levels in isolated cochlear outer hair cells of guinea pigs

Effects of intracellular pH (pHi) on intracellular Ca2+ (Cai2+) in the outer hair cell (OHC) were investigated using fluorescence ratio imaging microscopy. Cai2+ and pHi were determined with fluorescence indicators fura-2 and 2,7-bis(2-carboxyethyl)- 5,6-carboxyfluorescein, respectively. Intracellular alkalinization from the basal pHi of 7.22 +/- 0.03 to 7.82 +/- 0.09 (n = 7) induced by 25 mM NH4+ caused a rise in Cai2+ from 102 +/- 15 to 195 +/- 28 nM (n = 8). The elevation of Cai2+ was inhibited by removing external Ca2+ or by 50 microM nifedipine. On the other hand, the cytosolic acidification produced by the removal of NH4+ (delta pHi = 0.53 +/- 0.06, n = 7) and the admission of 5% CO2 (delta pHi = 0.72 +/- 0.05, n = 4) elicited a slight reduction in Cai2+. The depolarization of the membrane potential by exposure to 100 mM K+ induced an increase in Cai2+ that was susceptible to nifedipine, indicating the presence of voltage-sensitive Ca2+ channels. The elevation in Cai2+ induced by 100 mM K(+)-containing solution was increased by 138 +/- 6% (n = 4) by external alkalinization to pH 8.4 and was decreased by 87 +/- 3% (n = 4) by external acidification to pH 6.4. These results demonstrate that both internal and external alkalinization of OHCs facilitate the influx of Ca2+ through the Ca2+ channel, leading to a rise of Cai2+. Thus pH, extra- and intracellular, may modulate the OHC motility by regulating the Cai2+.

Cytosolic acidification leads to Ca2+ mobilization from intracellular stores in single and populational parietal cells and platelets

Regulatory relationship and gain control between cytosolic free Ca2+ concentration (Cai) and cytosolic pH (pHi) were evaluated by two different cell types, gastric parietal cells, and blood platelets. Studies were carried out in both single cells and populations of cells, using Ca2(+)-indicative probe fura-2 (1-(2-(5'-carboxyoxazol-2'-yl)-6-aminobenzofuran-5-oxy)-2-(2 '-amino-5'- methylphenoxy)ethane-N,N,N',N'-tetraacetic acid) and pH-indicative probe BCECF (2',7'-bis(carboxyethyl)carboxyfluorescein). Stimulation of single and populational parietal cells and platelets with gastrin and thrombin, respectively, resulted in an increase in Cai. In both populational cell types, an initial change in pHi during agonist stimulation occurred almost simultaneously with the mobilization of Ca2+; an initial transient decrease in pHi was followed by a slower increase in pHi above the prestimulation level. When populational platelets were preloaded with the Ca2+ chelator BAPTA (1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid), the thrombin-induced initial large increase in Cai was apparently inhibited, whereas the pHi decrease induced by thrombin was not altered. This suggests that the initial Cai change is not a prerequisite for the pHi change. The effect of pHi on Cai was examined next. In both single and populational cell types, application of the K(+)-H+ ionophore nigericin, which induced a transient decrease in pHi, led to the release of Ca2+ from intracellular stores. In single parietal cells double-labeled with fura-2 and BCECF, a temporal decrease in pHi preceded the rise in Cai after stimulation with nigericin. A decrease in pHi and an increase in Cai occurred at 1.5 and 4 s, respectively. In single parietal cells, replacement of medium Na+ with N-methyl-D-glucamine (NMG+), which also induced a decrease in pHi, resulted in repetitive Ca2+ spike oscillations. The source of Ca2+ utilized for the Ca2+ oscillation that was induced by NMG+ originated from the agonist-sensitive pool. Thus, several maneuvers, which were capable of decreasing pHi, led to an increase in Cai. Cytosolic acidification may be a part of the trigger for Ca2+ mobilization from intracellular stores in both parietal cells and platelets.

Heat induces intracellular acidification in human A-431 cells: role of Na(+)-H+ exchange and metabolism

The resting intracellular pH (pHi) of A-431 cells at 37 degrees C in Na+ Hanks' solution is 7.23 +/- 0.02. In the presence of amiloride (100 microM) pHi decreases to 7.08 +/- 0.03. Hyperthermia induces a temperature- and time-dependent intracellular acidification of 0.2 pH units in either bicarbonate-free or bicarbonate-buffered solutions. After heat treatment (45 degrees C, 10 min) pHi returns to normal 1 h after incubation at 37 degrees C. The activity of the Na(+)-H+ exchanger was examined in heated and unheated cells in the absence of bicarbonate. Unheated cells recover from an acid load in a [Na+]o-dependent and amiloride-sensitive manner. The apparent Michaelis constant for extracellular Na+ is 38 +/- 9 mM, and the apparent mean affinity constant for amiloride is 11 +/- 3 microM. In heated cells the apparent affinity of the Na(+)-H+ exchanger for extracellular Na+ is not changed, but the maximal recovery rate is approximately 40% slower than that of unheated cells. The rate of recovery from acid loading returns to normal 2 h after heat treatment. [Na+]i and intrinsic buffering power in heated cells are the same as those in unheated cells. Decreases in both intracellular ATP and lactic acid are observed in heated cells. 2-Deoxy-D-glucose and sodium azide induce an intracellular acidification but prevent most of the acidification induced by heat. Heat treatment causes no further acidification in cells that are acidified by both amiloride and 2-deoxy-D-glucose together. These data are the first to suggest that thermally induced intracellular acidification is due to both an inhibition of Na(+)-H+ exchange and an inhibition of metabolic pathways.

Measurement of intracellular calcium and pH in avian neural crest cells

1. Intracellular pH (pHi) and calcium (Cai2+) were studied in freely migrating neural crest cells and in closely packed non-migrating cells derived from avian neural tubes in vitro, using the fluorescent dyes 2,3-dicyanohydroquinone (DCH) and Indo-1 to measure pHi and Cai2+ respectively. 2. In freely migrating crest cells the pHi was approximately 0.2 pH units more alkaline and Cai2+ 90 nM lower than in closely packed cells. 3. Experiments to establish the cellular mechanisms regulating pHi in isolated neural crest cells demonstrate the presence of Na(+)-H+ exchange in 66% of the cells and Na(+)-HCO3(-)-dependent pHi-regulating mechanisms in all cells examined. 4. Interactions between pHi and Cai2+ were examined. pHi was altered using either NH4Cl pulses resulting in small changes in Cai2+ or using a weak acid and base (propionate and trimethylamine), which produced a fall and a rise in Cai2+ respectively. 5. Exposure to Ca2(+)-free media caused a lowering of Cai2+ and induced a transient acidification. 6. Application of BAPTA-AM (50 microM), a cell-permeant analogue of EGTA, resulted in a fall in Cai2+ and an intracellular acidification. 7. Co2+ and La3+ (2 mM) each induced a reversible fall in Cai2+ that was accompanied by intracellular acidification. These data suggest the presence of a transmembrane flux of Ca2+ in the resting cells. 8. It would appear that the mechanisms influencing Cai2+ and pHi are linked. This idea is discussed in terms of possible mechanisms and roles for Ca2+ and pH as modulators of neural crest cell behaviour.