Ion channels are fundamental molecules in the nervous system that catalyze the flux of ions across the cell membrane. There are mounting evidences suggesting that the kinetic properties of ion channels undergo activity-dependent changes in various pathophysiological conditions. Here such activity-dependent changes were studied in case of two different ion channels; the rat brain derived voltage-gated Na+ channel, rNav1.2 and the human background leak K+ channel, hTREK1 using the single channel patch-clamp technique. Our results on the voltage-gated Na+ channel (Chapter III) illustrated that sustained membrane depolarization, as seen in pathophysiological conditions like epilepsy, induced a defined non-linear variation in the unitary conductance, activation, inactivation and recovery kinetic properties of the channel. Signal processing tools attributed a pseudo-oscillatory nature to the non-linearity observed in the channel properties. Prolonged membrane depolarization also induced a “molecular memory” phenomenon, characterized by clustering of dwell time events and strong autocorrelation in the dwell time series. The persistence of such molecular memory was found to be dependent on the duration of depolarization. Similar plastic changes were observed in case of the hTREK1 channel in presence of saturating concentrations of agonist, trichloroethanol (TCE) (Chapter IV). TREK1 channel behaves similar to single enzyme molecules with a single binding site for the substrate K+ ion whereas TCE acts as an allosteric activator of the channel. We observed that with increasing concentration of TCE (10 M to 10 mM) the catalytic turnover rate exhibited progressive departure from monoexponential to multi-exponential distribution suggesting the presence of ‘dynamic disorder’ analogous to single enzyme molecules. In addition, we observed the induction of strong correlation in successive waiting times and flux intensities, exemplified by distinct mode switching between high and low flux activity, which implied the induction of memory in single ion channel. Our observation of such molecular memory in two different ion channels in different experimental conditions highlights the importance and generality of the phenomenon which is normally hidden under the ensemble behaviour of ion channels. In the final part of the work (chapter V) we observed strong negative cooperativity and half-of-sites saturation kinetics in the interaction of local anesthetic, lidocaine with hTREK1 channel. We also mapped the specific anesthetic binding site in the c-terminal domain of the channel. Further, single channel analysis and the heterodimer studies enabled us to propose a model for this interaction and provide a plausible paradigm for the inhibitory action of lidocaine on hTREK1.

Nicotinic acetylcholine receptors (nAChRs) are a major class of ligand-gated ion channels in the brain, with the α7 subtype of nAChRs playing an important role in attention, working memory and synaptic plasticity. Alterations in expression of α7 nAChRs are observed in neurological disorders including schizophrenia and Alzheimer’s disease. Therefore, understanding the fundamentals of how α7 nAChRs are regulated will increase our comprehension of how α7 nAChRs influence neuronal excitability, cognition and the pathophysiology of various neurological disorders. The purpose of this thesis was to investigate how protein kinases modulate the function and trafficking of α7 nAChRs in CNS neurons. In chapter 2, I describe a novel fast agonist applicator that I developed to reliably elicit α7 nAChR currents in both brain slices and cultured cells. In chapter 3, I examined whether an immune protein in the brain, the T-cell receptor (TCR), can modulate α7 nAChR activity. Activation of TCRs decreased α7 nAChR whole-cell recorded currents from layer 1 prefrontal cortical (PFC) neurons. TCR attenuated α7 nAChR currents through the activation of Fyn and Lck tyrosine kinases, which targeted tyrosine 442 in the M3-M4 cytoplasmic loop of α7. The mechanisms of the attenuated α7 current were contributed by a TCR mediated decrease in surface receptor expression and an attenuation of the α7 single-channel conductance. TCR stimulation also resulted in a decrease in neuronal excitability by negatively modulating α7 activity. In chapter 4, I tested whether PKA can modulate α7 nAChR function in CNS neurons. The pharmacological agents PKA agonist 8-Br-cAMP and PKA inhibitor KT-5720, as well as over-expressing dominant negative PKA and the catalytic subunit of PKA, demonstrated that activation of PKA leads to a reduction of α7 nAChR currents in HEK 293T cells and layer 1 cortical interneurons. Serine 365 of the M3-M4 cytoplasmic domain of α7 was necessary for the PKA modulation of α7. The mechanism of down-regulation in α7 receptor function was due to decreased surface receptor expression but not alterations in single-channel conductance nor gating kinetics. The results of this thesis demonstrate that α7 nAChRs constitute a major substrate for modulation via TCR activated tyrosine kinases and the cyclic AMP/PKA pathway. / Graduate / kpragya2000504@gmail.com

As a central component of the hypothalamic-pituitary-adrenal (HPA) axis, the anterior pituitary corticotrophs play an important role in the regulation of HPA axis function and the neuroendocrine response to stress. Pituitary corticotrophs integrate stress-induced stimulatory signals (CRH and AVP) from the brain together with the negative feedback control from circulating glucocorticoid hormones to coordinate adrenocorticotrophin hormone (ACTH) secretion. Previous studies have classified pituitary corticotrophs as both endocrine and electrically excitable cells with a number of ion channels and signaling pathways implicated in the control of their electrical properties and ACTH secretion. However, the mechanisms involved in native corticotrophs are poorly understood partly due to the current limitations of identifying physiological intact corticotrophs. To address the electrophysiological properties of native murine corticotrophs, a lentiviral transduction system was developed, using a minimal pro-opiomelanocortin (POMC) promoter to drive the expression of enhanced yellow fluorescent protein (eYFP), to allow highly efficient and specific labeling and identification of corticotrophs in vitro. This approach, with patch clamp electrophysiological investigations, revealed metabolically intact native murine corticotrophs displayed spontaneous action potentials with highly heterogeneous firing patterns including single spikes and variable “pseudo plateau bursting” action potentials. The resting membrane potential of native murine corticotrophs was maintained by a TTXresistant background sodium conductance. Physiological concentrations of CRH/AVP rapidly depolarized native murine corticotrophs resulting in a sustained increase in the frequency of action potentials. Native murine corticotrophs express multiple outward potassium conductances with two major components mediated by intermediate-conductance calcium-activated (SK4) potassium channels and A-type potassium channels. Inhibition of SK4 channels with TRAM-34 lead to an increase in corticotroph excitability with firing pattern transition from single spikes to “pseudo plateau bursting”. When A-type potassium channels were blocked, the afterhyperpolarization amplitude of single spikes was decreased in some corticotrophs. In native murine corticotrophs, outward potassium current carried by large conductance calcium- and voltage- activated potassium (BK) channels was very low, which is in contrast with that in the mouse pituitary adenoma cell line (AtT20 cell line). Corticotroph cells from wild type (WT) mice and mice with a genetic deletion of the BK channel (BK-/-) were compared. The only potassium current that showed significant difference between WT and BK-/- corticotrophs was carried via the barium-sensitive inwardly rectifying (Kir) potassium channel. However, the blockage of Kir channels displayed no clear effect on corticotroph cell electrical excitability. Similar heterogeneous spontaneous firing patterns were found in WT and BK-/- corticotrophs. Taken together, the lentiviral-mediated expression of eYFP, driven by a minimal POMC promoter, provides an efficient method to identify physiological intact native murine anterior pituitary corticotrophs. These findings demonstrate that native murine anterior pituitary corticotrophs are spontaneous excitable cells that display significant heterogeneity of firing patterns. Results also reveal an important role of a background TTX-insensitive sodium conductance in controlling spontaneous and CRH/AVP evoked action potentials. Furthermore, an unexpected role for SK4 calcium-activated potassium channels in corticotroph excitability was revealed. In all, these studies give new insight into the physiology of corticotroph excitability and ACTH secretion, and provide the basis for understanding the roles of these ion channels in HPA axis function.

In bacteria, mechanosensitive ion channels are essential for the cellular response to hypoosomitic shock, relieving the build up of membrane pressure. This thesis focuses on the Mechanosensitive Channel of Small Conductance (MscS) for which three conflicting gating models exist. These models were generated from structural studies of the closed and open conformations of MscS using three different experimental techniques. Pulsed Electron Double Resonance (PELDOR) spectroscopy was applied to MscS in the detergent solubilised state and the membrane-like bilayer. The distances between selectively introduced unpaired electrons in MscS were measured. PELDOR data in the detergent solubilised state were only consistent with the crystal structure depicting an open conformation of MscS, indicating that the transmembrane helices were unperturbed during crystallisation in detergent. MscS was reconstituted into membrane bilayer mimics, bicelles and nanodiscs, and PELDOR data in these environments suggested that both closed and open conformations determined by X-ray crystallography are stabilised in the membrane bilayer. The second part of this thesis involved stabilisation of an enzyme complex of the ubiquitin (Ub) pathway for structural analysis. This pathway is a eukaryotic signalling system involving post-translational modification of target protein amino groups with Ub. The variety of modification provided by Ub and its interplay with other Small Ubiquitin-like Modifier (SUMO) signalling proteins controls an array of cellular responses. The pathway functions to activate the Ub C-terminus, forming highly reactive thioester conjugates between Ub and the active site cysteine of a series of enzymes: E1, E2 and in some cases E3. This thesis explores the use of an isopeptide linkage to stabilise an E2~Ub conjugate in complex with an E3 enzyme. Sample conditions were optimised for the future use of PELDOR spectroscopy to structurally analyse the E2~Ub alone and in complex with E3.

5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) was normally recognised as a Cl- channel inhibitor, but its specificity is in question, since an inhibitory effect against K⁺ channels has been reported. To identify the significance of the molecules structural components, NPPB and related compounds, such as 2-(3-phenylpropylamino) benzoic acid (PPAB), 5- nitro-2-heptylamino benzoic acid (HANB) and 2-nitro-5-heptylamino benzoic acid (HANB-2) were synthesised by reductive amination using various aldehydes and amines. Using internodal cells of the giant green Characean algae, Nitella hookeri, the effects of NPPB and related compounds on cytoplasmic streaming and turgor regulation were determined. Previous experiments stated that cytoplasmic streaming was sensitive to NPPB, PPAB and HANB with IC₅₀ values of 24µmol/L, 455µmol/L, and 6.4mmol/L, respectively. In this report, the IC₅₀ values of purchased NPPB and niflumic acid were found to be 88.65µmol/L and 121.82µmol/L, respectively. Although the IC₅₀ value of purchased NPPB showed a slight difference from that of synthesised NPPB, the results of the cytoplasmic streaming experiment indicated the possibility of this analysis to be a simple assay system for analysing the effects of structural modification to ion channel inhibitors on their biological activity. Moreover, NPPB and PPAB seem to stimulate regulation of turgor pressure under hyperosmotic shock, which can be explained by a blockage of K⁺ efflux during osmotic stress leading to faster recovery of turgor regulation. Additionally, the results of cytosolic free Ca²⁺ analysis using aequorin technology also suggested that the possibility of this analysis to be used as a more direct measure of the inhibitory effect, while the cytoplasmic streaming analysis is a more indirect method. The preliminary results from this research suggest the significance of the simple assay systems for analysing the effects of structural modification ion channel inhibitors, which can be used for future study regarding ion channel structures.

Calcium (Ca2+) influx through N-methyl-D-asparate receptors (NMDARs) is widely held to be the requisite step initiating delayed neuronal death following ischemic stroke. However, blocking NMDARs fails to prevent the accumulation of intracellular Ca2+ ([Ca2+]i) and subsequent neurotoxicity. This suggests that alternate, as yet uncharacterized Ca2+-influx pathways exist in neurons. Transient receptor melastatin 2 (TRPM2) is a Ca2+-permeable member of the transient receptor potential melastatin family of cation channels whose activation by reactive oxygen/nitrogen species (ROS/RNS) and ADP-ribose (ADPR) is linked to cell death. While these channels are broadly expressed in the central nervous system (CNS), the presence of TRPM2 in neurons remains controversial and more specifically, whether they are expressed in neurons of the hippocampus is an open question. Here, I employ a combination of molecular, biochemical and electrophysiological approaches to demonstrate that functional TRPM2 channels are expressed in pyramidal neurons of the hippocampus. Unlike in heterologous expression systems, the ADPR-dependent activation of TRPM2 in neurons required a concomitant rise in [Ca2+]i via either voltage-dependent Ca2+ channels or NMDARs. While short, repeated NMDA applications activated a TRPM2-like current in the absence of exogenous ADPR, sustained NMDA application to hippocampal neurons resulted in the activation of a pannexin1 (Px1) hemichannel. Px1 hemichannels are large conductance, nonjunctional gap junction channels that can be activated following periods of oxygen-glucose deprivation (OGD) in neurons. Activation of Px1 required the influx of Ca2+ through NMDARs. Supplementing the intracellular milieu with adenosine triphosphate (ATP) prevented Px1 activation, suggesting that hemichannels may be activated during periods of mitochondrial dysfunction and metabolic failure. Our findings have potential implications for the treatment of diseases such as cerebral ischemia and Alzheimer’s disease (AD) as they implicate two novel ion channels in the excitotoxic signaling cascade activated downstream of NMDARs.

The bacterial mechanosensitive channels MscS and MscL have been shown to protect cells from hypo-osmotic shock-induced lysis. Bacterial strains deficient for MscS and MscL are severely compromised and fail to survive a hypo-osmotic shock. Both channels exhibit redundant function such that re-introduction of either of these proteins is sufficient to restore cell survival. Several proteins paralogous to MscS have been identified in E. coli, but their function remains unknown. Mechanosensitive channel homologues are also being discovered in a variety of organisms including Archaea, plants and fungi and their function is starting to emerge.

Recent evidence has indicated that NSAIDs might have direct effects on CNS tissue in addition to their classical inhibitory action on COX enzymes. This thesis addresses this hypothesis using electrophysiological and behavioural techniques. The effects of fenamate and other NSAIDs on native neuronal GABA(_A), 5-HT(_3), nicotinic ACh, P2x and strychinine-sensitive glycine receptors, expressed on isolated vagus or optic nerves, was investigated using an extra-cellular recording technique. The fenamate NSAID, mefenamic acid (MFA) potentiated GABA (10µM)- evoked responses in the vagus nerve. Application of MFA also resulted in non-competitive inhibition of 5-HT-and a,βMeATP- evoked responses. Non-competitive like inhibition was also observed with flufenamic acid on DMPP- and a,βMeATP- evoked responses and with meclofenamic acid on GABA- evoked responses. Non-fenamate NSAIDs, including aspirin, did not significantly modulate the GABA(_A), 5-HT(_3), nicotinic ACh, P2x or glycine receptors. The cognitive and behavioural effects of fenamates and other NASIDs were then investigated. MFA (5-20mg/kg) caused a significant dose- and time-dependent enhancement in the non-spatial object discrimination working memory task when compared to saline controls. The enhancement observed with MFA was greater than that of the cognitive enhancer piracetam. This enhancement was not due to a change in non-mnemonic processes such as arousal, anxiety or locomotion. MFA also enhanced rats' performance in the spatial object location working memory task. The fenamate NSAID, meclofenamic acid (20mg/kg) mimicked the effect of MFA, but the non-fenamate NSAIDs aspirin and ibuprofen, did not enhance object discrimination indicating that these cognitive effects are not via inhibition of COX. The GABA(_A) receptor modulators diazepam, bicuculline and loreclezole, did not replicate the effect of MFA on object discrimination, suggesting that its effects do not depend entirely on the GABAa receptor. Scopolamine (0.25-lmg/kg) significantly impaired object discrimination in a dose-dependent manner. This action could be fully reversed by co-treatment with MFA (20mg/kg).In the T-maze task, MFA (20mg/kg) decreased the number of arm entry errors and days taken to reach criterion. The number of arm entry errors made when a 5-minute intra-trial interval was introduced was also significantly reduced by MFA compared with saline treated animals. In the radial maze, MFA (20mg/kg) did not decrease the number of never baited arm entries to reach criterion. However MFA did significantly reduce the number of re-entry errors to baited arms, compared to controls, when an intra-trial delay (10-30 sees) was introduced. These results support the hypothesis that MFA enhances spatial working memory and that these effects are not task-specific. Overall, the data in this thesis show that fenamate NSAIDs can directly modulate native neuronal ligand-gated ion channels and that MFA can enhance working memory in normal and scopolamine-impaired rats. These results suggest additional pharmacological potential for certain fenamate NSAIDs.

Charles University in Prague Faculty of Pharmacy in Hradec Králové Department of Pharmaceutical Chemistry and Drug Control Student: Šárka Tomanová Supervisors: Prof. PharmDr. Martin Doležal, Ph.D., Prof. Dr. Christa Elisabeth Müller Title of diploma thesis: Development of a reliable test system for purinergic P2X3 receptors Purinergic P2X3 receptor is a ligand-gated ionotropic channel that occurs in all mammalian tissues. The highest occurrence has been observed in central and peripheral nervous system and smooth muscles, where P2X3 receptors participate in pathological disorders such as visceral and neurophatic pain, inflammatory reactions and psychiatric disorders. Compounds capable of blocking P2X3 receptor activity could be therefore used as potential drugs for treatment of these states. P2X3 receptor belongs to fast- desensitizing ionotropic channels, which makes the measurement of its activity very difficult. It was described that one point S15V mutation, in which the amino acid serine in a position 15 is replaced by amino acid valine, slows down the desensitization rate and the signal becomes easily measurable. This simple mutation may be used as an effective tool for characterization of insufficiently explored P2X3 receptor. The P2X3 S15V receptor DNA was inserted into retrovirus and,...

Chan Ling Nga. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 143-153). / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgements --- p.vi / Table of Contents --- p.vii / List of Figures --- p.xi / List of Tables --- p.xiv / Abbreviations --- p.xv / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- The Human Endometrium --- p.1 / Chapter 1.1.1 --- The Structure of the Endometrium --- p.1 / Chapter 1.1.2 --- Cyclic Changes in the Endometrium --- p.1 / Chapter 1.1.3 --- Physiological Roles of the Endometrium --- p.5 / Chapter 1.1.4 --- Roles of Luminal Epithelium in Implantation --- p.5 / Chapter 1.1.5 --- Exocrine Functions of the Endometrial Epithelium --- p.6 / Chapter 1.2 --- Review of Epithelial Ion Channels --- p.8 / Chapter 1.2.1 --- Epithelial Na+ Channels (ENaC) in Absorbing Epithelia --- p.9 / Chapter 1.2.2 --- Epithelial C1- Channels in Secretory Epithelia --- p.13 / Chapter 1.2.3 --- Na+ and C1- Channels in Endometrial Epithelia --- p.15 / Chapter 1.3 --- Review of the Intracellular Signal Transduction Pathways --- p.15 / Chapter 1.3.1 --- The cAMP-Mediated Signal Transduction Pathway --- p.17 / Chapter 1.3.2 --- The cAMP-Mediated Chloride Channels in Epithelial Cells --- p.17 / Chapter 1.3.3 --- Ca2+-Dependent Signal Transduction Pathway --- p.21 / Chapter 1.4 --- Physiological Roles of some Neurohormonal Agents in Uterine Functions: Selected Examples --- p.23 / Chapter 1.4.1 --- Roles of Adrenaline on the Endometrial Ion Transport --- p.23 / Chapter 1.4.2 --- Prostaglandin (PG) E2 and PGF2α --- p.24 / Chapter 1.4.3 --- Biological Effect of Extracellular Nucleotides --- p.26 / Chapter 1.5 --- Objective of this Study --- p.28 / Chapter 2 --- Materials and Methods --- p.31 / Chapter 2.1 --- Materials --- p.31 / Chapter 2.1.1 --- Culture Media and Enzymes --- p.31 / Chapter 2.1.2 --- Drugs --- p.31 / Chapter 2.1.3 --- Chemicals --- p.32 / Chapter 2.1.4 --- Experimental Tissues and Animals --- p.32 / Chapter 2.2 --- Preparations --- p.32 / Chapter 2.2.1 --- Previous Support for Cell Growth --- p.32 / Chapter 2.2.2 --- Growth Medium --- p.33 / Chapter 2.2.3 --- Culture of Mouse Endometrial Epithelial Cells --- p.35 / Chapter 2.2.4 --- Solutions for the Short-Circuit Current Measurements --- p.36 / Chapter 2.2.5 --- Solutions for the Patch-Clamp Experiments --- p.38 / Chapter 2.2.6 --- Running Buffers for RNA and DNA Gel Electrophoresis --- p.39 / Chapter 2.2.7 --- UTP-free UDP --- p.40 / Chapter 2.2.8 --- Electrodes for the Short-Circuit Current Measurement --- p.40 / Chapter 2.3 --- Protocols --- p.41 / Chapter 2.3.1 --- Characterization of Neurohormonal Agents-induced Ion Channels --- p.41 / Chapter 2.3.2 --- Possible Interaction between CFTR and ENaC --- p.41 / Chapter 2.3.3 --- Characterization of Pyrimidinoceptors-mediated Conductances --- p.42 / Chapter 2.4 --- Methods of Measurements --- p.42 / Chapter 2.4.1 --- The Patch-Clamp Technique --- p.42 / Chapter 2.4.1.1 --- The Patch-Clamp Setup --- p.43 / Chapter 2.4.1.2 --- Shielding and Grounding --- p.45 / Chapter 2.4.1.3 --- Pipette Fabrication --- p.45 / Chapter 2.4.1.4 --- Pipette Holder and Electrodes --- p.48 / Chapter 2.4.1.5 --- Experimental Procedures --- p.49 / Chapter 2.4.1.6 --- Signal Recording and Data Acquisition --- p.54 / Chapter 2.4.1.7 --- Data Analysis --- p.54 / Chapter 2.4.2 --- The Short-Circuit Current Technique --- p.55 / Chapter 2.4.2.1 --- The Short-Circuit Current Setup --- p.56 / Chapter 2.4.2.2 --- Experimental Procedures --- p.56 / Chapter 2.4.2.3 --- Data Analysis --- p.61 / Chapter 2.4.3 --- Reverse Transciption - Polymerase Chain Reaction (RT-PCR) --- p.61 / Chapter 2.4.3.1 --- RNA Isolation --- p.61 / Chapter 2.4.3.2 --- RNA Gel Electrophoresis --- p.62 / Chapter 2.4.3.3 --- Reverse Transcription (RT) --- p.63 / Chapter 2.4.3.4 --- Polymerase Chain Reaction (PCR) --- p.64 / Chapter 2.4.3.5 --- DNA Gel Electrophoresis --- p.66 / Chapter 2.4.4 --- Statistical Analysis --- p.66 / Chapter 3 --- Results --- p.67 / Chapter 3.1 --- Activation of Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) in Response to Hormonal Stimuli --- p.67 / Chapter 3.2 --- Inhibition of Na+ Absorption by CFTR --- p.89 / Chapter 3.3 --- Pyrimidinoceptors-activated Ca2+-dependent C1- Conductance --- p.111 / Chapter 4 --- General Discussions --- p.132 / Appendix --- p.140 / Chapter A --- RNA Isolation --- p.140 / Chapter B --- Reverse Transcription --- p.141 / Chapter C --- Polymerase Chain Reaction --- p.142 / References --- p.143