Molecular Impact of Conventional and Electronic Cigarettes on Pulmonary Surfactant.

The alveolar epithelium is covered by a non-cellular layer consisting of an aqueous hypophase topped by pulmonary surfactant, a lipo-protein mixture with surface-active properties. Exposure to cigarette smoke (CS) affects lung physiology and is linked to the development of several diseases. The macroscopic effects of CS are determined by several types of cell and molecular dysfunction, which, among other consequences, lead to surfactant alterations. The purpose of this review is to summarize the published studies aimed at uncovering the effects of CS on both the lipid and protein constituents of surfactant, discussing the molecular mechanisms involved in surfactant homeostasis that are altered by CS. Although surfactant homeostasis has been the topic of several studies and some molecular pathways can be deduced from an analysis of the literature, it remains evident that many aspects of the mechanisms of action of CS on surfactant homeostasis deserve further investigation.

Blood Thiol Redox State in Chronic Kidney Disease.

Thiols (sulfhydryl groups) are effective antioxidants that can preserve the correct structure of proteins, and can protect cells and tissues from damage induced by oxidative stress. Abnormal levels of thiols have been measured in the blood of patients with moderate-to-severe chronic kidney disease (CKD) compared to healthy subjects, as well as in end-stage renal disease (ESRD) patients on haemodialysis or peritoneal dialysis. The levels of protein thiols (a measure of the endogenous antioxidant capacity inversely related to protein oxidation) and S-thiolated proteins (mixed disulphides of protein thiols and low molecular mass thiols), and the protein thiolation index (the molar ratio of the S-thiolated proteins to free protein thiols in plasma) have been investigated in the plasma or red blood cells of CKD and ESRD patients as possible biomarkers of oxidative stress. This type of minimally invasive analysis provides valuable information on the redox status of the less-easily accessible tissues and organs, and of the whole organism. This review provides an overview of reversible modifications in protein thiols in the setting of CKD and renal replacement therapy. The evidence suggests that protein thiols, S-thiolated proteins, and the protein thiolation index are promising biomarkers of reversible oxidative stress that could be included in the routine monitoring of CKD and ESRD patients.

Effects of Physiological and Pathological Urea Concentrations on Human Microvascular Endothelial Cells.

Urea is the uremic toxin accumulating with the highest concentration in the plasma of chronic kidney disease (CKD) patients, not being completely cleared by dialysis. Urea accumulation is reported to exert direct and indirect side effects on the gastrointestinal tract, kidneys, adipocytes, and cardiovascular system (CVS), although its pathogenicity is still questioned since studies evaluating its side effects lack homogeneity. Here, we investigated the effects of physiological and pathological urea concentrations on a human endothelial cell line from the microcirculation (Human Microvascular Endothelial Cells-1, HMEC-1). Urea (5 g/L) caused a reduction in the proliferation rate after 72 h of exposure and appeared to be a potential endothelial-to-mesenchymal transition (EndMT) stimulus. Moreover, urea induced actin filament rearrangement, a significant increase in matrix metalloproteinases 2 (MMP-2) expression in the medium, and a significant up- or down-regulation of other EndMT biomarkers (keratin, fibrillin-2, and collagen IV), as highlighted by differential proteomic analysis. Among proteins whose expression was found to be significantly dysregulated following exposure of HMEC-1 to urea, dimethylarginine dimethylaminohydrolase (DDAH) and vasorin turned out to be down-regulated. Both proteins have been directly linked to cardiovascular diseases (CVD) by in vitro and in vivo studies. Future experiments will be needed to deepen their role and investigate the signaling pathways in which they are involved to clarify the possible link between CKD and CVD.

Protein carbonylation in human bronchial epithelial cells exposed to cigarette smoke extract.

Cigarette smoke is a well-established exogenous risk factor containing toxic reactive molecules able to induce oxidative stress, which in turn contributes to smoking-related diseases, including cardiovascular, pulmonary, and oral cavity diseases. We investigated the effects of cigarette smoke extract on human bronchial epithelial cells. Cells were exposed to various concentrations (2.5-5-10-20%) of cigarette smoke extract for 1, 3, and 24 h. Carbonylation was assessed by 2,4-dinitrophenylhydrazine using both immunocytochemical and Western immunoblotting assays. Cigarette smoke induced increasing protein carbonylation in a concentration-dependent manner. The main carbonylated proteins were identified by means of two-dimensional electrophoresis coupled to MALDI-TOF mass spectrometry analysis and database search (redox proteomics). We demonstrated that exposure of bronchial cells to cigarette smoke extract induces carbonylation of a large number of proteins distributed throughout the cell. Proteins undergoing carbonylation are involved in primary metabolic processes, such as protein and lipid metabolism and metabolite and energy production as well as in fundamental cellular processes, such as cell cycle and chromosome segregation, thus confirming that reactive carbonyl species contained in cigarette smoke markedly alter cell homeostasis and functions.

Antiestrogen- and tamoxifen-induced effects on calcium-activated chloride currents in epithelial cells carrying the ∆F508-CFTR point mutation.

BACKGROUND: Although pharmacological treatment has increased the average life expectancy of patients with cystic fibrosis, the median survival of females is shorter than that of males. In vitro and in vivo studies have shown that estrogens play a relevant role in the disease progression. The aim of this study was to investigate the effects of 17ß-estradiol and tamoxifen citrate (TMX) on calcium-activated chloride channel (CaCC) currents in human bronchial epithelial cells carrying the ΔPhe508-CFTR mutation both in homozygosis and in heterozygosis. METHODS: Perforated patch clamp experiments were performed on single cells of the immortalized cell lines CFBE and IB3-1. Gramicidin (10 or 20 µM) was added to the electrode solution to reach the whole cell configuration. The electrical stimulation protocol consisted of square voltages ranging from - 80 to + 80 mV, in steps of 20 mV and with a duration of 800 msec. RESULTS: The presence of 17ß-estradiol significantly reduced the CaCC currents, both in basal conditions and in the presence of ATP (100 µM). The addition of TMX (10 µM) completely restored the currents abolished by 17ß-estradiol, in basal conditions and after stimulation with ATP in both CFBE and IB3-1 cells. TMX had a strong, direct action on membrane current density, which significantly increased more than 4-fold in both cases. The membrane current stimulation produced by TMX was further enhanced by the addition of ATP. CFBE cells incubated for 24 h with 3 µM VX-809 (a CFTR corrector) and then acutely stimulated with VX-770 (a CFTR potentiator) in the presence of forskolin, showed an increase of chloride currents which were abolished by Inh-172. The chloride current density induced by TMX + ATP was, on average, greater than that obtained with VX-809 + VX-770 + forskolin. The currents elicited by TMX + ATP were abolished by the addition of NPPB, a CaCC inhibitor. The combined administration of TMX/ATP and VXs/FSK had an additional effect on chloride currents. CONCLUSIONS: Our results show that TMX restores CaCC currents inhibited by 17ß-estradiol and directly activates the transmembrane chloride currents potentiated by ATP, an effect which is mutation independent. The combined effect of TMX with current used treatments for cystic fibrosis could be of benefit to patients.

Assessment of glutathione/glutathione disulphide ratio and S-glutathionylated proteins in human blood, solid tissues, and cultured cells.

Glutathione (GSH) is the major non-protein thiol in humans and other mammals, which is present in millimolar concentrations within cells, but at much lower concentrations in the blood plasma. GSH and GSH-related enzymes act both to prevent oxidative damage and to detoxify electrophiles. Under oxidative stress, two GSH molecules become linked by a disulphide bridge to form glutathione disulphide (GSSG). Therefore, assessment of the GSH/GSSG ratio may provide an estimation of cellular redox metabolism. Current evidence resulting from studies in human blood, solid tissues, and cultured cells suggests that GSH also plays a prominent role in protein redox regulation via S -glutathionylation, i.e., the conjugation of GSH to reactive protein cysteine residues. A number of methodologies that enable quantitative analysis of GSH/GSSG ratio and S-glutathionylated proteins (PSSG), as well as identification and visualization of PSSG in tissue sections or cultured cells are currently available. Here, we have considered the main methodologies applied for GSH, GSSG and PSSG detection in biological samples. This review paper provides an up-to-date critical overview of the application of the most relevant analytical, morphological, and proteomics approaches to detect and analyse GSH, GSSG and PSSG in mammalian samples as well as discusses their current limitations.

Plasma protein-bound di-tyrosines as biomarkers of oxidative stress in end stage renal disease patients on maintenance haemodialysis.

BACKGROUND: Patients with end-stage renal disease (ESRD) undergoing haemodialysis (HD) experience enhanced oxidative stress and systemic inflammation, which are risk factors for cardiovascular disease, the most common cause of excess morbidity and mortality for these patients. Different pathways producing different types of oxidative stress occur in ESRD. The purpose of our study was to determine the effect of HD on plasma levels of protein-bound dityrosine (di-Tyr), a biomarker of protein oxidation. METHODS: Protein-bound di-Tyr formation was measured by size exclusion HPLC coupled to fluorescence detector. Clinical laboratory parameters were measured by standardized methods. RESULTS: In most ESRD patients, a single HD session decreased significantly the plasma protein-bound di-Tyr level, although the mean post-HD level remained significantly greater than the one in healthy people. Furthermore, pre-HD plasma protein-bound di-Tyr level was positively correlated with pre-HD serum creatinine and albumin concentrations. No significant correlation was found between plasma protein-bound di-Tyr level and serum concentration of C-reactive protein, a biomarker of systemic inflammation. CONCLUSIONS: This study demonstrates that a single HD session does not increase, rather partially decreases, oxidative pathways producing di-Tyr in the haemodialyzed patient. GENERAL SIGNIFICANCE: The choice of the most pertinent biomarkers of oxidative stress is critical for the development of novel treatments for ESRD. However, the relative importance of oxidative stress and inflammation in ESRD remains largely undetermined, and several questions concerning oxidative stress and inflammation remain poorly defined. These results could stimulate further studies on the use of plasma protein-bound di-Tyr as a long-lasting oxidative stress biomarker in ESRD.

Thiol oxidation and di-tyrosine formation in human plasma proteins induced by inflammatory concentrations of hypochlorous acid.

In this study, we assessed the oxidative damage occurring in plasma proteins when human blood was exposed to inflammatory concentrations of hypochlorous acid (HOCl). We used specific thiol labelling and Western blot analyses to determine protein thiol oxidation, as well as analytical gel filtration HPLC coupled to fluorescence detection to explore formation of high molecular weight (HMW) protein aggregates. Thiol-containing proteins oxidized by HOCl were identified by redox proteomics. Mass spectrometry (MS) analysis was performed to elucidate the protein composition of HMW aggregates. α1-antitrypsin, transthyretin, and haptoglobin showed thiol oxidation at HOCl concentrations higher than those causing complete oxidation of albumin. At the highest HOCl concentrations, formation of carbonylated and di-tyrosine cross-linked HMW protein aggregates also occurred. MS analysis identified fibrinogen, complement C3 and apolipoprotein A-I as components of HMW protein aggregates. These results could be relevant for human diseases characterized by inflammatory conditions in which myeloperoxidase and HOCl are involved. BIOLOGICAL SIGNIFICANCE: In this study we evaluated the oxidative damage occurring on plasma proteins when reconstituted human blood was exposed to inflammatory concentrations of hypochlorous acid (HOCl). Pathophysiological concentrations of HOCl are able to induce different modifications on plasma proteins such as carbonylation, sulfhydryl oxidation and formation of high molecular weight (HMW) protein aggregates characterized by di-tyrosine fluorescence. There are two relevant aspects emerging from this paper. The first one consists on identifying low abundant proteins undergoing sulfhydryl oxidation by biotin-maleimide derivatization followed by MALDI-TOF mass spectrometry. This approach suggests three low-abundant proteins undergoing HOCl-induced oxidation: transthyretin, α1-antitrypsin, and haptoglobin. In addition, we analysed HMW protein aggregates forming after HOCl exposure. These aggregates are characterized by carbonylation, intra- and/or intermolecular di-tyrosine bridges. After their isolation from SDS-PAGE gel electrophoresis, using electrospray tandem mass spectrometry coupled to reversed-phase nanoscale capillary liquid chromatography, we identified some protein constituents of these HMW aggregates such as α, ß, γ fibrinogen chains, apolipoprotein A-I and complement C3. In particular, our work highlights how fibrinogen is an important constituent of HOCl-induced HMW protein aggregates validating the mass spectrometry result with additional experiments. Further investigations are required in order to evaluate the possibility to use carbonylated and di-Tyr cross-linked HMW protein aggregates as (early) biomarkers for disease progression in inflammatory conditions in which myeloperoxidase and HOCl are involved.

Plasma protein thiolation index (PTI) as a biomarker of thiol-specific oxidative stress in haemodialyzed patients.

The role of oxidative stress in patients with end stage renal disease (ESRD), which occurs at significantly higher levels than in the general population, is often underestimated in clinical practice. Emerging evidence highlights the strong correlation of oxidative stress with chronic inflammation and cardiovascular disease, which are highly prevalent in most patients on maintenance haemodialysis (HD) and are a major risk factor for mortality in this population. In this study, total plasma thiols and plasma S-thiolated proteins were measured in patients with ESRD, before and after a regular HD session, and compared to age-matched healthy subjects. We found a significant decrease in the level of total plasma thiols and, conversely, a significant increase in the level of S-thiolated proteins in these patients. In most patients, post-HD plasma level of total thiols did not differ from the one in healthy subjects, whereas plasma level of S-thiolated proteins was lower in HD patients than in age-matched healthy controls. This suggests that a single HD session restores plasma thiol redox status and re-establishes the antioxidant capacity of plasma thiols. Additionally, we determined protein thiolation index (PTI), i.e., the molar ratio between the sum of all low molecular mass thiols bound to S-thiolated plasma proteins and protein free cysteinyl residues. Patients with ESRD had a significantly higher PTI compared to age-matched healthy subjects and HD was associated with a decrease in PTI to normal, or lower than normal, levels. Although this study is limited in size, our results suggest that PTI is a useful indicator of thiol-specific oxidative stress in patients with ESRD on maintenance HD. This study also emphasizes that PTI determination is a cheap and simple tool suitable for large-scale clinical studies that could be used for routine screening of thiol-specific oxidative stress.

ICln: a new regulator of non-erythroid 4.1R localisation and function.

To optimise the efficiency of cell machinery, cells can use the same protein (often called a hub protein) to participate in different cell functions by simply changing its target molecules. There are large data sets describing protein-protein interactions ("interactome") but they frequently fail to consider the functional significance of the interactions themselves. We studied the interaction between two potential hub proteins, ICln and 4.1R (in the form of its two splicing variants 4.1R80 and 4.1R135), which are involved in such crucial cell functions as proliferation, RNA processing, cytoskeleton organisation and volume regulation. The sub-cellular localisation and role of native and chimeric 4.1R over-expressed proteins in human embryonic kidney (HEK) 293 cells were examined. ICln interacts with both 4.1R80 and 4.1R135 and its over-expression displaces 4.1R from the membrane regions, thus affecting 4.1R interaction with ß-actin. It was found that 4.1R80 and 4.1R135 are differently involved in regulating the swelling activated anion current (ICl,swell) upon hypotonic shock, a condition under which both isoforms are dislocated from the membrane region and thus contribute to ICl,swell current regulation. Both 4.1R isoforms are also differently involved in regulating cell morphology, and ICln counteracts their effects. The findings of this study confirm that 4.1R plays a role in cell volume regulation and cell morphology and indicate that ICln is a new negative regulator of 4.1R functions.

Short- and long- term effects of cigarette smoke exposure on glutathione homeostasis in human bronchial epithelial cells.

BACKGROUND: Cigarette smoke extract (CSE), a model for studying the effects of tobacco smoke in vivo and in vitro, induces cell oxidative stress and affects the antioxidative glutathione system. We evaluated the impact of CSE on airway epithelial cells and the possible cytoprotective effect of the mucolitic drug S-carboximethilcysteine lysine salt (S-CMC-Lys). METHODS: Reduced glutathione (GSH) and reactive oxygen species (ROS) intracellular levels were evaluated by fluorimetry in human bronchial epithelial cells (16-HBE) and the expression and activity of enzymes of the GSH metabolic pathway were investigated by RT-PCR, Western blot and colorimetric assays. RESULTS: CSE significantly increased cell mortality in a time and dose dependent manner, via an apoptosis-independent pathway. Short-term (3 hours) CSE exposure induced an increase in ROS levels and a GSH intracellular concentration drop. In parallel, the expression of glutathione peroxidases 2 and 3, glutathione reductase and glutamate-cysteine-ligase was increased. S-CMC-Lys was effective in counteracting these effects. CONCLUSION: CSE affects ROS levels, GSH concentration and GSH enzymes pathway. These effects can be to some extent reversed by S-CMC-Lys, that could represent a therapeutic tool to counteract CSE induced oxidative cellular injuries.

Hypertension-linked mutation of α-adducin increases CFTR surface expression and activity in HEK and cultured rat distal convoluted tubule cells.

The CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) activity and localization are influenced by the cytoskeleton, in particular by actin and its polymerization state. In this study we investigated whether the expression of the hypertensive mutations of α-adducin (G460W-S586C in humans, F316Y in rats), an actin capping protein, led to a functional modification of CFTR activity and surface expression. The experiments were performed on HEK293 T cells cotransfected with CFTR and the human wild type (WT) or G460W mutated α-adducin. In whole-cell patch-clamp experiments, both the CFTR chloride current and the slope of current activation after forskolin addition were significantly higher in HEK cells overexpressing the G460W adducin. A higher plasma membrane density of active CFTR channels was confirmed by cell-attached patch-clamp experiments, both in HEK cells and in cultured primary DCT cells, isolated from MHS (Milan Hypertensive Strain, a Wistar rat (Rattus norvegicus) hypertensive model carrying the F316Y adducin mutation), compared to MNS (Milan Normotensive Strain) rats. Western blot experiments demonstrated an increase of the plasma membrane CFTR protein expression, with a modification of the channel glycosylation state, in the presence of the mutated adducin. A higher retention of CFTR protein in the plasma membrane was confirmed both by FRAP (Fluorescence Recovery After Photobleaching) and photoactivation experiments. The present data indicate that in HEK cells and in isolated DCT cells the presence of the G460W-S586C hypertensive variant of adducin increases CFTR channel activity, possibly by altering its membrane turnover and inducing a retention of the channel in the plasmamembrane. Since CFTR is known to modulate the activity of many others transport systems, the increased surface expression of the channel could have consequences on the whole network of transport in kidney cells.

S-CMC-Lys protective effects on human respiratory cells during oxidative stress.

The mucoactive drug S-carbocysteine lysine salt monohydrate (S-CMC-Lys) stimulates glutathione (GSH) efflux from respiratory cells. Since GSH is one of the most important redox regulatory mechanisms, the aim of this study was to evaluate the S-CMC-Lys effects on GSH efflux and intracellular concentration during an oxidative stress induced by the hydroxyl radical (xOH). Experiments were performed on cultured human respiratory WI-26VA4 cells by means of patch-clamp experiments in whole-cell configuration and of fluorimetric analyses at confocal microscope. xOH exposure induced an irreversible inhibition of the GSH and chloride currents that was prevented if the cells were incubated with S-CMC-Lys. In this instance, the currents were inhibited by the specific blocker CFTR(inh)-172. CFT1-C2 cells, which lack a functional CFTR channel, were not responsive to S-CMC-Lys, but the stimulatory effect of the drug was restored in LCFSN-infected CFT1 cells, functionally corrected to express CFTR. Fluorimetric measurements performed on the S-CMC-Lys-incubated cells revealed a significant increase of the GSH concentration that was completely hindered after oxidative stress and abolished by CFTR(inh)-172. The cellular content of reactive oxygen species was significantly lower in the S-CMC-Lys-treated cells either before or after xOH exposure. As a conclusion, S-CMC-Lys could exert a protective function during oxidative stress, therefore preventing or reducing the ROS-mediated inflammatory response.

Upregulation of apical sodium-chloride cotransporter and basolateral chloride channels is responsible for the maintenance of salt-sensitive hypertension.

We investigated which of the NaCl transporters are involved in the maintenance of salt-sensitive hypertension. Milan hypertensive (MHS) rats were studied 3 mo after birth. In MHS, compared with normotensive strain (MNS), mRNA abundance, quantified by competitive PCR on isolated tubules, was unchanged, both for Na+/H+ isoform 3 (NHE3) and Na+-K+-2Cl- (NKCC2), but higher (119%, n = 5, P < 0.005) for Na+-Cl- (NCC) in distal convoluted tubules (DCT). These results were confirmed by Western blots, which revealed: 1) unchanged NHE3 in the cortex and NKCC2 in the outer medulla; 2) a significant increase (52%, n = 6, P < 0.001) of NCC in the cortex; 3) alpha- and beta-sodium channels [epithelial Na+ channel (ENaC)] unaffected in renal cortex and slightly reduced in the outer medulla, while gamma-ENaC remained unchanged. Pendrin protein expression was unaffected. The role of NCC was reinforced by immunocytochemical studies showing increased NCC on the apical membrane of DCT cells of MHS animals, and by clearance experiments demonstrating a larger sensitivity (P < 0.001) to bendroflumethiazide in MHS rats. Kidney-specific chloride channels (ClC-K) were studied by Western blot experiments on renal cortex and by patch-clamp studies on primary culture of DCT dissected from MNS and MHS animals. Electrophysiological characteristics of ClC-K channels were unchanged in MHS rats, but the number of active channels in a patch was 0.60 +/- 0.21 (n = 35) in MNS rats and 2.17 +/- 0.59 (n = 23) in MHS rats (P < 0.05). The data indicate that, in salt-sensitive hypertension, there is a strong upregulation, both of NCC and ClC-K along the DCT, which explains the persistence of hypertension.

The expression of wild-type pendrin (SLC26A4) in human embryonic kidney (HEK 293 Phoenix) cells leads to the activation of cationic currents.

OBJECTIVE: The SLC26A4 protein (pendrin) seems to be involved in the exchange of chloride with other anions, therefore being responsible for iodide organification in the thyroid gland and the conditioning of the endolymphatic fluid in the inner ear. Malfunction of SLC26A4 leads to Pendred syndrome, characterized by mild thyroid dysfunction often associated with goiter and/or prelingual deafness. The precise function of the SLC26A4 protein, however, is still elusive. An open question is still whether the SLC26A4-induced ion exchange mechanism is electrogenic or electroneutral. Recently, it has been shown that human pendrin expressed in monkey cells leads to chloride currents. METHODS: We overexpressed the human SLC26A4 isoform in HEK293 Phoenix cells and measured cationic and anionic currents by the patch-clamp technique in whole cell configuration. RESULTS: Here we show that human pendrin expressed in human cells does not lead to the activation of chloride currents, but, in contrast, leads to an increase of cationic currents. CONCLUSION: Our experiments suggest that the SLC26A4-induced chloride transport is electroneutral when expressed in human cellular systems.

ICln159 folds into a pleckstrin homology domain-like structure. Interaction with kinases and the splicing factor LSm4.

ICln is a multifunctional protein involved in regulatory mechanisms as different as membrane ion transport and RNA splicing. The protein is water-soluble, and during regulatory volume decrease after cell swelling, it is able to migrate from the cytosol to the cell membrane. Purified, water-soluble ICln is able to insert into lipid bilayers to form ion channels. Here, we show that ICln159, a truncated ICln mutant, which is also able to form ion channels in lipid bilayers, belongs to the pleckstrin homology (PH) domain superfold family of proteins. The ICln PH domain shows unusual properties as it lacks the electrostatic surface polarization seen in classical PH domains. However, similar to many classical PH domain-containing proteins, ICln interacts with protein kinase C, and in addition, interacts with cAMP-dependent protein kinase and cGMP-dependent protein kinase type II but not cGMP-dependent protein kinase type Ibeta. A major phosphorylation site for all three kinases is Ser-45 within the ICln PH domain. Furthermore, ICln159 interacts with LSm4, a protein involved in splicing and mRNA degradation, suggesting that the ICln159 PH domain may serve as a protein-protein interaction platform.

Mechanisms sensing and modulating signals arising from cell swelling.

Cell volume alterations are involved in numerous cellular events like epithelial transport, metabolic processes, hormone secretion, cell migration, proliferation and apoptosis. Above all it is a need for every cell to counteract osmotic cell swelling in order to avoid cell damage. The defence against excess cell swelling is accomplished by a reduction of the intracellular osmolarity by release of organic- or inorganic osmolytes from the cell or by synthesis of osmotically less active macromolecules from their specific subunits. De-spite the large amount of experimental data that has accumulated, the intracellular mechanisms underlying the sensing of cell volume perturbations and the activation of volume compensatory processes, commonly summarized as regulatory volume decrease (RVD), are still only partly revealed. Moving into this field opens a complex scenario of molecular rearrangements and interactions involving intracellular messengers such as calcium, phosphoinositides and inositolphosphates as well as phosphoryla-tion/dephosphorylation processes and cytoskeletal reorganization with marked cell type- and tissue specific variations. Even in one and the same cell type significant differences regarding the activated pathways during RVD may be evident. This makes it virtually im-possible to unambigously define common sensing- and sinaling pathways used by differ-ent cells to readjust their celll volume, even if all these pathways converge to the activa-tion of comparatively few sets of effectors serving for osmolyte extrusion, including ion channels and transporters. This review is aimed at providing an insight into the manifold cellular mechanisms and alterations occuring during cell swelling and RVD.

ICln channels reconstituted in heart-lipid bilayer are selective to chloride.

ICln is an ion channel cloned from renal epithelial cells. The reconstitution of the protein in 1,2-diphytanoyl- sn-glycero-3-phosphocholine (Diph-PC) bilayer membranes reveals potassium-selective channels, which become more chloride selective in the presence of calcium. Here we show that the ion selectivity of ICln also depends on the lipid environment in which the channels are reconstituted. Diph-PC is a synthetic lipid commonly used for reconstituting ion channels. However, since this lipid is not found in native membranes, we reconstituted the ICln ion channels in a polar heart-lipid extract. Using this lipid mixture the reconstituted ICln ion channels are chloride selective in the presence of calcium and an acidic pH. The relative ion selectivity of ICln under these conditions is similar to the cation versus anion selectivity of native ion channels activated by cell swelling.

K+ channel cAMP activated in guinea pig gallbladder epithelial cells.

In guinea pig gallbladder epithelial cells, an increase in intracellular cAMP levels elicits the rise of anion channel activity. We investigated by patch-clamp techniques whether K(+) channels were also activated. In a cell-attached configuration and in the presence of theophylline and forskolin or 8-Br-cAMP in the cellular incubation bath, an increase of the open probability (P(o)) values for Ca(2+)-activated K(+) channels with a single-channel conductance of about 160 pS, for inward current, was observed. The increase in P(o) of these channels was also seen in an inside-out configuration and in the presence of PKA, ATP, and cAMP, but not with cAMP alone; phosphorylation did not influence single-channel conductance. In the inside-out configuration, the opioid loperamide (10(-5) M) was able to reduce P(o) when it was present either in the microelectrode filling solution or on the cytoplasmic side. Detection in the epithelial cells by RT-PCR of the mRNA corresponding to the alpha subunit of large-conductance Ca(2+)-activated K(+) channels (BK(Ca)) indicates that this gallbladder channel could belong to the BK family. Immunohistochemistry experiments confirm that these cells express the BK alpha subunit, which is located on the apical membrane. Other K(+) channels with lower conductance (40 pS) were not activated either by 8-Br-cAMP (cell-attached) or by PKA + ATP + cAMP (inside-out). These channels were insensitive to TEA(+) and loperamide. The data demonstrate that under conditions that induce secretion, phosphorylation activates anion channels as well as Ca(2+)-dependent, loperamide-sensitive K(+) channels present on the apical membrane.