Beata Dworakowska

Large-conductance K+ channel openers NS1619 and NS004 as inhibitors of mitochondrial function in glioma cells

Recently, it has been reported that large-conductance Ca(2+)-activated potassium channels, also known as BK(Ca)-type potassium channels, are present in the inner mitochondrial membrane of the human glioma LN229 cell line. Hence, in the present study, we have investigated whether BK(Ca)-channel openers (BK(Ca)COs), such as the benzimidazolone derivatives NS004 (5-trifluoromethyl-1-(5-chloro-2-hydroxyphenyl)-1,3-dihydro-2H-benzimidazole-2-one) and NS1619 (1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazol-2-one), affect the functioning of LN229 glioma cell mitochondria in situ. We examined the effect of BK(Ca)COs on mitochondrial membrane potential, mitochondrial respiration and plasma membrane potassium current in human glioma cell line LN229. We found that BK(Ca)COs decrease the mitochondrial membrane potential with an EC(50) value of 3.6+/-0.4 microM for NS1619 and 5.4+/-0.8 microM for NS004. This mitochondrial depolarization was accompanied by an inhibition of the mitochondrial respiratory chain. Both BK(Ca)COs induced whole-cell potassium current blocked by charybdotoxin, as measured by the patch-clamp technique. The BK(Ca)COs had no effect on membrane bilayer conductance. Moreover, the inhibition of mitochondrial function by NS004 and NS1619 was without effect on cell survival, as measured by lactate dehydrogenase release from the cells.

Piezometric biosensors for anti-apoptotic protein survivin based on buried positive-potential barrier and immobilized monoclonal antibodies.

The anti-apoptotic protein survivin (Sur) plays an important role in the regulation of cell division and inducing the chemotherapeutic drug resistance. The Sur protein and its mRNA have recently been studied as cancer biomarkers and potential targets for cancer therapy. In this work, we have focused on the design of immunosensors for the detection of Sur based on buried positive-potential barrier layer structure and anti-survivin antibody. The modification of solid AuQC piezoelectrodes was monitored by recording the resonance frequency shift and electrochemical measurements during each step of the sensor preparation. Our results indicate that the immunosensor with covalently bound monoclonal anti-survivin antibody can detect Sur with the limit of detection, LOD=1.7nM (S/N=3σ). The immunosensor applicability for the analysis of real samples was assessed by testing samples of cell lysate solutions obtained from human astrocytoma (glioblastoma) U-87MG cell line, with the experiments performed using the standard addition method. The good linearity of the calibration curves for PBS and lysate solutions at low Sur concentrations confirm the high specificity of the proposed biosensor and good discrimination against nonspecific interactions with lysate components. The calculations indicate that there is still room to increase the Sur capture capacity for Sur while miniaturizing the sensor. The important advantage of the sensor is that it can be reused by a simple regeneration procedure.

On the simple random-walk models of ion-channel gate dynamics reflecting long-term memory.

Several approaches to ion-channel gating modelling have been proposed. Although many models describe the dwell-time distributions correctly, they are incapable of predicting and explaining the long-term correlations between the lengths of adjacent openings and closings of a channel. In this paper we propose two simple random-walk models of the gating dynamics of voltage and Ca2+-activated potassium channels which qualitatively reproduce the dwell-time distributions, and describe the experimentally observed long-term memory quite well. Biological interpretation of both models is presented. In particular, the origin of the correlations is associated with fluctuations of channel mass density. The long-term memory effect, as measured by Hurst R/S analysis of experimental single-channel patch-clamp recordings, is close to the behaviour predicted by our models. The flexibility of the models enables their use as templates for other types of ion channel.

Mitochondria-based biosensors with piezometric and RELS transduction for potassium uptake and release investigations.

Dysfunctional mitochondria appear to be involved in many diseases through their role in respiration, reactive oxygen species generation, and energy production. To aid in the design of new biosensors based on mitochondria (MT), we have investigated the feasibility of detecting ion fluxes through the MT-membrane K+-ion channels using piezosensors with MTs immobilized either by hydrogen bonding or thin polypyrrole (PPy) binding film. We have demonstrated for the first time that the mitochondria-based piezosensors are able to detect ion fluxes and thus be utilized for drug development aimed at ion channel opener- or inhibitor-function. The quartz crystal resonator responding only to mass changes in the lower part of the MT film, penetrated by the acoustic wave, is able to detect a pronounced cationic dynamics in PPy-bonded MT piezosensors despite of the undoped-PPy preference for pure anion dynamics. The control experiments performed by resonance elastic light scattering (RELS) confirmed MT swelling/shrinking, ion dynamics, and osmotic water transfer in MTs, as well as the effects of exposure to a drug valinomycin at sub-nanomolar concentrations.

The H-loop in the Second Nucleotide-binding Domain of the Cystic Fibrosis Transmembrane Conductance Regulator is Required for Efficient Chloride Channel Closing

The cystic fibrosis transmembrane conductance regulator (CFTR) is an ATP-binding cassette (ABC) transporter that functions as a cAMP-activated chloride channel. The recent model of CFTR gating predicts that the ATP binding to both nucleotide-binding domains (NBD1 and NBD2) of CFTR is required for the opening of the channel, while the ATP hydrolysis at NBD2 induces subsequent channel closing. In most ABC proteins, efficient hydrolysis of ATP requires the presence of the invariant histidine residue within the H-loop located in the C-terminal part of the NBD. However, the contribution of the corresponding region (H-loop) of NBD2 to the CFTR channel gating has not been examined so far. Here we report that the alanine substitution of the conserved dipeptide HR motif (HR→AA) in the H-loop of NBD2 leads to prolonged open states of CFTR channel, indicating that the H-loop is required for efficient channel closing. On the other hand, the HR→AA substitution lead to the substantial decrease of CFTR-mediated current density (pA/pF) in transfected HEK 293 cells, as recorded in the whole-cell patch-clamp analysis. These results suggest that the H-loop of NBD2, apart from being required for CFTR channel closing, may be involved in regulating CFTR trafficking to the cell surface.

Potassium currents in human myogenic cells from donors of different ages

Ageing in humans is accompanied by a reduction in the capacity of satellite cells to proliferate and the forming myoblasts to fuse. The processes of myoblast differentiation and fusion are associated with specific changes in the cells electrical properties. We wanted to elucidate the possible effects of ageing on these parameters and performed whole-cell patch-clamp recordings on human myoblasts obtained from biopsies of skeletal muscles from 2-, 48- and 76-year-old donors. First, we found that resting membrane potential on the 4th day of differentiation in vitro is less negative in the older than in the younger cells. Moreover, the oldest cells showed a smaller density of outward and inward potassium currents. More cells from the old and middle-age donors have a low (less than -40 mV) potential of activation for the outward potassium current. We conclude that in human myoblasts biophysical properties of potassium currents change with donor age.

Optical Biosensing System for the Detection of Survivin mRNA in Colorectal Cancer Cells Using a Graphene Oxide Carrier-Bound Oligonucleotide Molecular Beacon

The anti-apoptotic protein survivin is one of the most promising cancer biomarkers owing to its high expression in human cancers and rare occurrence in normal adult tissues. In this work, we have investigated the role of supramolecular interactions between a graphene oxide (GO) nanosheet nanocarrier and a survivin molecular beacon (SurMB), functionalized by attaching fluorophore Joe and quencher Dabcyl (SurMB-Joe). Molecular dynamics simulations revealed hydrogen bonding of Joe moiety and Dabcyl to GO carriers that considerably increase the SurMB-GO bonding strength. This was confirmed in experimental work by the reduced fluorescence background in the OFF state, thereby increasing the useful analytical signal range for mRNA detection. A new mechanism of hairpin–hairpin interaction of GO@SurMB with target oligonucleotides has been proposed. A low limit of detection, LOD = 16 nM (S/N = 3), has been achieved for complementary tDNA using GO@SurMB-Joe nanocarriers. We have demonstrated an efficient internalization of SurMB-Joe-loaded GO nanocarriers in malignant SW480 cells. The proposed tunability of the bonding strength in the attached motifs for MBs immobilized on nanocarriers, via structural modifications, should be useful in gene delivery systems to enhance the efficacy of gene retention, cell transfection and genomic material survivability in the cellular environment.

Hairpin–Hairpin Molecular Beacon Interactions for Detection of Survivin mRNA in Malignant SW480 Cells

Cancer biomarkers offer unique prospects for the development of cancer diagnostics and therapy. One of such biomarkers, protein survivin (Sur), exhibits strong antiapoptotic and proliferation-enhancing properties and is heavily expressed in multiple cancers. Thus, it can be utilized to provide new modalities for modulating the cell-growth rate, essential for effective cancer treatment. Herein, we have focused on the development of a new survivin-based cancer detection platform for colorectal cancer cells SW480 using a turn-on fluorescence oligonucleotide molecular beacon (MB) probe, encoded to recognize Sur messenger RNA (mRNA). Contrary to the expectations, we have found that both the complementary target oligonucleotide strands as well as the single- and double-mismatch targets, instead of exhibiting the anticipated simple random conformations, preferentially formed secondary structure motifs by folding into small-loop hairpin structures. Such a conformation may interfere with, or even undermine, the biorecognition process. To gain better understanding of the interactions involved, we have replaced the classical Tyagi-Kramer model of interactions between a straight target oligonucleotide strand and a hairpin MB with a new model to account for the hairpin-hairpin interactions as the biorecognition principle. A detailed mechanism of these interactions has been proposed. Furthermore, in experimental work, we have demonstrated an efficient transfection of malignant SW480 cells with SurMB probes containing a fluorophore Joe (SurMB-Joe) using liposomal nanocarriers. The green emission from SurMB-Joe in transfected cancer cells, due to the hybridization of the SurMB-Joe loop with Sur mRNA hairpin target, corroborates Sur overexpression. On the other hand, healthy human-colon epithelial cells CCD 841 CoN show only negligible expression of survivin mRNA. These experiments provide the proof-of-concept for distinguishing between the cancer and normal cells by the proposed hairpin-hairpin interaction method. The single nucleotide polymorphism sensitivity and a low detection limit of 26 nM (S/N = 3σ) for complementary targets have been achieved.

Restoration of the response of the middle cerebral artery of the rat to acidosis in hyposmotic hyponatremia by the opener of large-conductance calcium sensitive potassium channels (BKCa)

Hyposmotic hyponatremia (the decrease of extracellular concentration of sodium ions from 145 to 121 mM and the decrease of hyposmolality from 300 to 250 mOsm/kg H2O) impairs response of the middle cerebral artery (MCA) to acetylcholine and NO donor (S-nitroso-N-acetyl-DL-penicillamine). Since acidosis activates a similar intracellular signaling pathway, the present study was designed to verify the hypothesis that the response of the MCA to acidosis is impaired during acute hyposmotic hyponatremia due to abnormal NO-related signal transduction in vascular smooth muscle cells. Studies performed on isolated, cannulated, and pressurized rat MCA revealed that hyposmotic hyponatremia impaired the response of the MCA to acidosis and this was associated with hyposmolality rather than with decreased sodium ion concentration. Response to acidosis was restored by the BKCa but not by the KATP channel activator. Patch-clamp electrophysiology performed on myocytes freshly isolated from MCAs, demonstrated that hyposmotic hyponatremia does not affect BKCa currents but decreases the voltage-dependency of the activation of the BKCa channels in the presence of a specific opener of these channels. Our study suggests that reduced sensitivity of BKCa channels in the MCA to agonists results in the lack of response of this artery to acidosis during acute hyposmotic hyponatremia.

POTASSIUM CURRENTS IN HUMAN MYOGENIC CELLS FROM HEALTHY AND CONGENITAL MYOTONIC DYSTROPHY FOETUSES

The whole-cell patch clamp technique was used to record potassium currents in in vitro differentiating myoblasts isolated from healthy and myotonic dystrophy type 1 (DM1) foetuses carrying 2000 CTG repeats. The fusion of the DM1 myoblasts was reduced in comparison to that of the control cells. The dystrophic muscle cells expressed less voltage-activated K+ (delayed rectifier and non-inactivating delayed rectifier) and inward rectifier channels than the age-matched control cells. However, the resting membrane potential was not significantly different between the control and the DM1 cells. After four days in a differentiation medium, the dystrophic cells expressed the fast-inactivating transient outward K+ channels, which were not observed in healthy cells. We suggest that the low level of potassium currents measured in differentiated DM1 cells could be related to their impaired fusion.