BK Channels – Focus on Polyamines, Ethanol/Acetaldehyde and Hydrogen Sulfide (H2S)

(VLID)386021

S100 Calcium Binding Proteins and Ion Channels

S100 Ca2+-binding proteins have been associated with a multitude of intracellular Ca2+-dependent functions including regulation of the cell cycle, cell differentiation, cell motility and apoptosis, modulation of membrane–cytoskeletal interactions, transduction of intracellular Ca2+ signals, and in mediating learning and memory. S100 proteins are fine tuned to read the intracellular free Ca2+ concentration and affect protein phosphorylation, which makes them candidates to modulate certain ion channels and neuronal electrical behavior. Certain S100s are secreted from cells and are found in extracellular fluids where they exert unique extracellular functions. In addition to their neurotrophic activity, some S100 proteins modulate neuronal electrical discharge activity and appear to act directly on ion channels. The first reports regarding these effects suggested S100-mediated alterations in Ca2+ fluxes, K+ currents, and neuronal discharge activity. Recent reports revealed direct and indirect interactions with Ca2+, K+, Cl−, and ligand activated channels. This review focuses on studies of the physical and functional interactions of S100 proteins and ion channels

Mechanisms of Two Modulatory Actions of the Channel-binding Protein Slob on the Drosophila Slowpoke Calcium-dependent Potassium Channel

Slob57 is an ion channel auxiliary protein that binds to and modulates the Drosophila Slowpoke calcium-dependent potassium channel (dSlo). We reported recently that residues 1–39 of Slob57 comprise the key domain that both causes dSlo inactivation and shifts its voltage dependence of activation to more depolarized voltages. In the present study we show that removal of residues 2–6 from Slob57 abolishes the inactivation, but the ability of Slob57 to rightward shift the voltage dependence of activation of dSlo remains. A synthetic peptide corresponding in sequence to residues 1–6 of Slob57 blocks dSlo in a voltage- and dose-dependent manner. Two Phe residues and at least one Lys residue in this peptide are required for the blocking action. These data indicate that the amino terminus of Slob57 directly blocks dSlo, thereby leading to channel inactivation. Further truncation to residue Arg16 eliminates the modulation of voltage dependence of activation. Thus these two modulatory actions of Slob57 are independent. Mutation within the calcium bowl of dSlo greatly reduces its calcium sensitivity (Bian, S., I. Favre, and E. Moczydlowski. 2001. Proc. Natl. Acad. Sci. USA. 98:4776–4781). We found that Slob57 still causes inactivation of this mutant channel, but does not shift its voltage dependence of activation. This result confirms further the independence of the inactivation and the voltage shift produced by Slob57. It also suggests that the voltage shift requires high affinity Ca2+ binding to an intact calcium bowl. Furthermore, Slob57 inhibits the shift in the voltage dependence of activation of dSlo evoked by Ca2+, and this inhibition by Slob57 is greater at higher free Ca2+ concentrations. These results implicate distinct calcium-dependent and -independent mechanisms in the modulation of dSlo by Slob

Phosphorylation of BK channels modulates the sensitivity to hydrogen sulfide (H2S)

Introduction: Gases, such as nitric oxide (NO), carbon monoxide (CO) or hydrogen sulfide (H2S), termed gasotransmitters, play an increasingly important role in understanding of how electrical signaling of cells is modulated. H2S is well known to act on various ion channels and receptors. In a previous study we reported that H2S increased calcium-activated potassium (BK) channel activity. Aims: The goal of the present study is to investigate the modulatory effect of BK channel phosphorylation on the action of H2S on the channel as well as to recalculate and determine the H2S concentrations in aqueous sodium hydrogen sulfide (NaHS) solutions.Methods: Single channel recordings of GH3, GH4 and GH4 STREX cells were used to analyze channel open probability, amplitude and open dwell times. H2S was measured with ananion selective electrode. Results: The concentration of H2S produced from NaHS was recalculated taking pH, temperature salinity of the perfusate and evaporation of H2S into account. The results indicate that from a concentration of 300 µM NaHS, only11-13%, i.e. 34-41 µM is effective as H2S in solution. GH3, GH4 and GH4 STREX cells respond differently to phosphorylation. BK channel open probability (Po) of all cells lines used was increased by H2S in ATP containing solutions. PKA prevented the action of H2S on channel Po in GH4 and GH4 STREX, but not in GH3 cells. H2S, high significantly increased Po of all PKG pretreated cells. In the presence of PKC, which lowers channel activity, H2S increased channel Po of GH4 and GH4 STREX, but not those of GH3 cells. H2S increased open dwell times of GH3 cells in the absence of ATP significantly. A significant increase of dwell times with H2S was also observed in the presence of okadaic acid.Conclusions: Our results suggest that phosphorylation by PKG primes the channels for H2S activation and indicate that channel phosphorylation plays an important role in the response to H2S

Is Consciousness Dissectible? Acute Slice Electrophysiology and a Bayesian Interpretation of Neural Correlates of Consciousness

The acute brain slicing method has become one of the foundations of modern neuroscience research. It is a laboratory technique in electrophysiology, which allows the study of electrical properties directly on a freshly prepared slice of animal brain tissue. During recording and/or stimulation, the acutely isolated brain slice is artificially kept “alive†up to many hours after the animals’ death. During an acute brain slice preparation, cortical and subcortical areas, which are suggested to correlate with conscious experience in humans, such as the claustrum and the thalamus, are dissected. In this paper, we investigate whether scientific statements can be made regarding the likelihood that some neural activities on the brain slice still support consciousness or degrees thereof.We exemplarily demonstrate how acute slices are produced and provide own electrophysiological data combined with a short literature review. Subsequently, we introduce the concept of Neural Correlates of Consciousness (NCC) and apply conditional probabilities inferred from Bayes´ theorem, in order to draw from it an informed hypothesis on the likelihood that specific neural activities that sustain on the slice still correlate with some form of conscious experience. We propose that the probability that there is something that is it like to be, even on the acutely isolated brain slice, is similar to the likelihood that certain mental states correlate with certain brain activities in a healthy human subject, depending on the robustness of the underlying NCC

Diffusion of peroxides through dentine in vitro with and without prior use of a desensitizing varnish

Different bleaching regimens are used in dentistry possibly penetrating the dentine and affecting the pulp. The aim of the present study was to investigate peroxide diffusion through dentine pre-treated with a desensitizing varnish (Vivasens®) in a standardized in vitro setup during application of different bleaching materials. The penetration was tested using 1.3-mm-thick bovine dentine slabs. The following bleaching materials were tested with and without prior application of the desensitizing varnish on the external side of the dentine slabs: Vivastyle, Whitestrips, Simply White, Opalescence (external bleaching), and sodium perborate (internal bleaching, only tested without varnish; n = 8 samples per subgroup). The penetration of peroxides was measured photometrically using 4-aminoantipyrin as a substrate, the penetration of peroxides was monitored over 240 min. All bleaching agents yielded a diffusion of peroxides through the dentine, the kinetics of penetration were approximately linear for all materials tested. The significantly highest diffusion of peroxides was observed with Opalescence, the lowest with sodium perborate. The adoption of the desensitizing varnish reduced the diffusion of peroxides significantly for all external bleaching materials. Peroxides penetrated the dentine during application of bleaching materials; the penetration of peroxides can be reduced by application of a desensitizing agent

BK Channels: Integrators of Cellular Signals in Health and Disease

Maxi calcium-activated potassium channels (BK) are an amazing category of ion channels which are found in cellular plasma membranes as well as in membranes of intracellular organelles. The function of these channels is to repolarize any excited membrane by passing a potassium outward current, in response to depolarization and/or increase in local calcium levels. Thus, voltage and calcium ions are involved in gating the channel under physiological conditions. This dual activation makes them perfect sensors for many cellular events that require integration between intracellular calcium levels and electrical signals. A plethora of physiological and pathophysiological functions, such as membrane hyperpolarization, modulation of synaptic transmission, hormone secretion or mental deficiencies, vaso-regulation, epilepsies, heart diseases, myotonic dystrophies, hypertension etc, in almost all cells and tissues were reported for these channels. BK channels are main targets for important ligands like alcohol and gaseous neurotransmitters, such as NO, CO or H2S, to name a few. In the last years, the molecular entities and mechanisms involved in modulation of BK channels have gained tremendous attention, as the key role of these channels in cellular processes became increasingly recognized. Indeed, accessory proteins such as slob, beta and gamma subunits, all serve to modulate the channel gating characteristics. Moreover, channel subunit expression and function is further tuned by phosphorylation/ dephosphorylation processes, redox mechanisms and the lipid microenvironment of the BK channel protein complex. This e-book contains structural and functional aspects of BK channels, channel modulation by a variety of agents and cellular components, as well as the channel’s relevance in health and disease

Oxidative Stress and Maxi Calcium-Activated Potassium (BK) Channels

All cells contain ion channels in their outer (plasma) and inner (organelle) membranes. Ion channels, similar to other proteins, are targets of oxidative impact, which modulates ion fluxes across membranes. Subsequently, these ion currents affect electrical excitability, such as action potential discharge (in neurons, muscle, and receptor cells), alteration of the membrane resting potential, synaptic transmission, hormone secretion, muscle contraction or coordination of the cell cycle. In this chapter we summarize effects of oxidative stress and redox mechanisms on some ion channels, in particular on maxi calcium-activated potassium (BK) channels which play an outstanding role in a plethora of physiological and pathophysiological functions in almost all cells and tissues. We first elaborate on some general features of ion channel structure and function and then summarize effects of oxidative alterations of ion channels and their functional consequences