pS Channel Research Articles

Dynamics of electron capture in positron‐hydrogen scattering under dense semi‐classical plasmas

AbstractThe scattering dynamics of electron capture in ‐H(1 s) scattering under dense semi‐classical plasma (DSCP) environments has been investigated theoretically. Coupled multi‐channel two‐body Lippmann‐Schwinger equations have been solved by retaining +H(1 s) and p + Ps(1 s) channels to calculate the cross sections (CS) of the electron capture process at intermediate and high incident energies. The effective interaction of the plasma charged particles is modelled by a pseudopotential which is a function of two parameters, namely the plasma screening strength and the de Broglie wavelength. A detailed study is made to explore the changes in the CSs of the above‐mentioned process with respect to the variation in the plasma screening strength and de Broglie wavelength. Significant changes are found to take place, when the screening strength and the de Broglie wavelength are varied. Specifically, the sharp minimum in the differential CS moves toward the forward direction with increasing de Broglie wavelength at a given screening strength.

Low-energy scattering properties of ground-state and excited-state positronium collisions

SynopsisLow-energy elastic and inelastic scattering in the Ps(1s)-Ps(2s) channel is treated in a four-body hyperspherical coordinate calculation. Adiabatic potentials are calculated for triplet-triplet, singlet-singlet, and singlet-triplet spin symmetries of coupled electrons and coupled positrons, with total angular momentum L = 0 and positive parity. Preliminary estimates of the s-wave scattering length in the elastic Ps(1s)-Ps(2s) channel were obtained. Spin recoupling is implemented to obtain calculations of experimentally relevant scattering properties for different Ps spin states.

Low-energy scattering properties of ground-state and excited-state positronium collisions

Low-energy elastic and inelastic scattering in the Ps(1$s$)-Ps(2$s$) channel is treated in a four-body hyperspherical coordinate calculation. Adiabatic potentials are calculated for triplet-triplet, singlet-singlet, and singlet-triplet spin symmetries in the spin representation of coupled electrons and coupled positrons, with total angular momentum $L=0$ and parity equal to $+1$. The s-wave scattering lengths for the asymptotic Ps(1$s$)-Ps(2$s$) channel are calculated for each spin configuration. Results obtained for the s-wave scattering lengths are $a_{\mathrm{TT}}=$~$7.3(2)a_0-i0.02(1)a_0$, $a_{\mathrm{SS}}=$~$13.2(2)a_0-i0.9(2)a_0$, and $a_{\mathrm{ST}}=$~$9.7(2)a_0$ for each spin configuration. Spin recoupling is implemented to extract the scattering lengths for collisions of Ps in different spin configurations through properly symmetrized unitary transformations. Calculations of experimentally relevant scattering lengths and cross-sections are carried-out for Ps atoms initially prepared in different uncoupled spin states.

The 70 pS Inward Rectifying K Channel Is Identified as Renal Outer Medullary K Channels (ROMK) on Rough, but not Smooth, Thick Ascending Limb Cells (TAL)

Previous studies revealed that ROMK was represented by two inward rectifying K‐selective channels (Kir) in the TAL, with single channel conductances of approximately 30 pS and 70 pS (inward currents). However, the mouse TAL contains two types of cells; rough TAL (R‐TAL), with abundant apical microvilli and smooth TAL (S‐TAL), which are absent of microvilli. We performed patch clamping, immunohistochemistry, and electron microscopy with immunogold in attempt to determine whether the 30 pS and/or 70 pS channels were associated with R‐TAL or S‐TAL. Cell‐attached patches with 140 mM KCl in the pipette, applied to the split‐open TAL from WT or ROMK knock‐out mice (KO) (one tubule/mouse and 4 to 9 patches per tubule), revealed the 30 pS Kir (31.1 ± 1.2 pS) with an open probability of 0.60 ± 0.09 (at −Vp = −40 mV) and a density of 20 channels out of 73 patches. The 70 pS Kir (74.0 ± 3.4 pS) was observed with Po of 0.35 ± 0.13, and with a density of 12 channels out of 73 patches. We found no patches that contained both channels despite a mathematical probability that 5 patches would contain both the 30 pS and 70 pS channels. We found no 70 pS channels in 42 patches of TAL from ROMK−/−. However, 17 channels were identified as the 30 pS Kir (34.2 ± 1.0) with a Po of 0.56 ± 0.06 (−Vp = −40 mV). Co‐immunohistochemical staining with anti‐ROMK (from Dr. Paul Welling) and anti‐Tamm‐Horsfall protein (TAL marker) revealed ROMK on the luminal membrane of only 40 to 60% of the TAL cells. Using immunogold‐labeled anti‐ROMK and transmission electron microscopy, we found that ROMK was associated with the R‐TAL but not S‐TAL. We conclude that the 70 pS, but not the 30 pS Kir, represents ROMK and the 70 pS Kir is predominantly localized on R‐TALSupport or Funding InformationThis project is supported by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) grants R01‐DK‐092474 and R01‐DK‐071014

Upregulation of basolateral small conductance potassium channels (KCNQ1/KCNE3) in ulcerative colitis

BackgroundBasolateral K+ channels hyperpolarize colonocytes to ensure Na+ (and thus water) absorption. Small conductance basolateral (KCNQ1/KCNE3) K+ channels have never been evaluated in human colon. We therefore evaluated KCNQ1/KCNE3 channels in distal colonic crypts obtained from normal and active ulcerative colitis (UC) patients. MethodsKCNQ1 and KCNE3 mRNA levels were determined by qPCR, and KCNQ1/KCNE3 channel activity in normal and UC crypts, and the effects of forskolin (activator of adenylate cyclase) and UC-related proinflammatory cytokines on normal crypts, studied by patch clamp recording. ResultsWhereas KCNQ1 and KCNE3 mRNA expression was similar in normal and UC crypts, single 6.8 pS channels were seen in 36% of basolateral patches in normal crypts, and to an even greater extent (74% of patches, P < 0.001) in UC crypts, with two or more channels per patch. Channel activity was 10-fold higher (P < 0.001) in UC crypts, with a greater contribution to basolateral conductance (5.85 ± 0.62 mS cm−2) than in controls (0.28 ± 0.04 mS cm−2, P < 0.001). In control crypts, forskolin and thromboxane A2 stimulated channel activity 30-fold and 10-fold respectively, while PGE2, IL-1β, and LTD4 had no effect. ConclusionsKCNQ1/KCNE3 channels make only a small contribution to basolateral conductance in normal colonic crypts, with increased channel activity in UC appearing insufficient to prevent colonic cell depolarization in this disease. This supports the proposal that defective Na+ absorption rather than enhanced Cl− secretion, is the dominant pathophysiological mechanism of diarrhea in UC.

Abstract 113: Renal Phenotype of Inwardly Rectifying Potassium Channel Kcnj16 (Kir 5.1) Knockout in the Dahl Salt-Sensitive Rats

The inward-rectifying channels play an important role in the control of resting membrane potential and tubular homeostasis in the kidney. Kcnj16 (Kir 5.1) form a heteromeric channel with Kcnj10 (Kir 4.1) at the basolateral membranes of aldosterone-sensitive distal nephron (ASDN); mutations in the human KCNJ10 gene result in SeSAME)/EAST syndrome, a complex disorder that includes salt wasting and hypokalemic alkalosis. To illuminate the importance of Kcnj16 (Kir 5.1) in the context of a disease state in vivo, we generated a Kcnj16 knockout rat model in Dahl salt-sensitive (SS) background by using ZFN technology. ZFN against Kcnj16 caused a 18-bp in-frame deletion that occurred in the second protein transmembrane domain. IHC analysis demonstrated highly specific expression of Kcnj16 on the basolateral membranes of ASDN in the control kidneys of SS rats, which was completely abolished in Kcnj16-/- rats. The electrophysiological recording of K+ channels in the CCD basolateral membrane revealed activity of only homomeric Kcnj10 channels (21 pS channel in Kcnj16-/- rats compared to both 41 and 21 pS channels in SS rats). Thus, these data provide evidence of successful knock out of this protein and consequent degradation of the channel in renal tubules. The Kcnj16-/- knockout in SS rat induces electrolyte imbalance, epileptic seizures and result in changes in development (37% reduction in body and 54% in kidney mass). The mean arterial pressure was significantly lower in Kcnj16-/- compared to SS rats (91.3±1.8 to 104.7±5.5 mmHg) when animals were fed a low salt (0.4%) diet. Knockout of Kcnj16 resulted in hypokalemia (4.25±0.09 vs 2.08±0.12 mmol/L in serum of control vs KO rats), hypermagnesemia (0.49±0.02 vs 0.63±0.01 mmol/L in serum of control vs KO rats), and FSGS. Urea electrolyte balance was also disturbed compared to control animals. Importantly, change of the diet to high salt (4%) caused mortality of KO rats within 1-2 days. These data demonstrate critical role of Kcnj16 channels in renal salt handling and in the development of salt-sensitive hypertension.

Microstructural and magnetic characterizations of CoFeCu electrodeposited in self-assembled mesoporous silicon

Abstract Self-assembled mesoporous silicon with quasi-regular pore arrangements has been fabricated by the electrochemical anodization process in hydrofluoric acid solution. CoFeCu was electrodeposited in this structure from a bath containing sodium acetate as a complexing agent with a pH value of 5. The effect of current density on the morphology, the structure and the magnetic properties of CoFeCu deposit was studied by SEM, EDS, DRX and VSM. It has been shown that the morphology and structure of samples were strongly influenced by the current density and etching duration. The micrographs show the vertical and branched nanowires and also a discontinuous growth of wires. Further, the growth of a thick layer from the grain boundaries of released CoFeCu wires is produced. The magnetic hysteresis loops demonstrate that the CoFeCu nanowires exhibit easy magnetic axis perpendicular to the PS channels axis when the current density varied from 3 to 10 mA/cm 2 . Nevertheless, they reveal a no magnetic anisotropy of CoFeCu nanostructures deposited only in the outside of porous silicon, probably due to the vanishing the shape anisotropy.

Highly efficient energy transfer from a carbonyl carotenoid to chlorophyll a in the main light harvesting complex of Chromera velia

We report on energy transfer pathways in the main light-harvesting complex of photosynthetic relative of apicomplexan parasites, Chromera velia. This complex, denoted CLH, belongs to the family of FCP proteins and contains chlorophyll (Chl) a, violaxanthin, and the so far unidentified carbonyl carotenoid related to isofucoxanthin. The overall carotenoid-to-Chl-a energy transfer exhibits efficiency over 90% which is the largest among the FCP-like proteins studied so far. Three spectroscopically different isofucoxanthin-like molecules were identified in CLH, each having slightly different energy transfer efficiency that increases from isofucoxanthin-like molecules absorbing in the blue part of the spectrum to those absorbing in the reddest part of spectrum. Part of the energy transfer from carotenoids proceeds via the ultrafast S2 channel of both the violaxanthin and isofucoxanthin-like carotenoid, but major energy transfer pathway proceeds via the S1/ICT state of the isofucoxanthin-like carotenoid. Two S1/ICT-mediated channels characterized by time constants of ~0.5 and ~4ps were found. For the isofucoxanthin-like carotenoid excited at 480nm the slower channel dominates, while those excited at 540nm employs predominantly the fast 0.5ps channel. Comparing these data with the excited-state properties of the isofucoxanthin-like carotenoid in solution we conclude that, contrary to other members of the FCP family employing carbonyl carotenoids, CLH complex suppresses the charge transfer character of the S1/ICT state of the isofucoxanthin-like carotenoid to achieve the high carotenoid-to-Chl-a energy transfer efficiency.

Increase in cytosolic Ca2+ produced by hypoxia and other depolarizing stimuli activates a non‐selective cation channel in chemoreceptor cells of rat carotid body

The current model of O2 sensing by carotid body chemoreceptor (glomus) cells is that hypoxia inhibits the outward K(+) current and causes cell depolarization, Ca(2+) influx via voltage-dependent Ca(2+) channels and a rise in intracellular [Ca(2+)] ([Ca(2+)]i). Here we show that hypoxia (<5% O2), in addition to inhibiting the two-pore domain K(+) channels TASK-1/3 (TASK), indirectly activates an ∼20pS channel in isolated glomus cells. The 20pS channel was permeable to K(+), Na(+) and Cs(+) but not to Cl(-) or Ca(2+). The 20pS channel was not sensitive to voltage. Inhibition of TASK by external acid, depolarization of glomus cells with high external KCl (20mm) or opening of the Ca(2+) channel with FPL64176 activated the 20pS channel when 1mm Ca(2+) was present in the external solution. Ca(2+) (10μm) applied to the cytosolic side of inside-out patches activated the 20pS channel. The threshold [Ca(2+)]i for activation of the 20pS channel in cell-attached patches was ∼200nm. The reversal potential of the 20pS channel was estimated to be -28mV. Our results reveal a sequential mechanism in which hypoxia (<5% O2) first inhibits the K(+) conductance and then activates a Na(+)-permeable, non-selective cation channel via depolarization-induced rise in [Ca(2+)]i. Our results suggest that inhibition of K(+) efflux and stimulation of Na(+) influx both contribute to the depolarization of glomus cells during moderate to severe hypoxia.

THIK-1 (K2P13.1) is a small-conductance background K+ channel in rat trigeminal ganglion neurons

The goal of this study was to determine the molecular identity of a small-conductance (~5-pS) background K(+) channel expressed in trigeminal ganglion (TG) neurons. We tested the hypothesis that the 5-pS channel is a K2P channel by comparing the pharmacological and single-channel properties of THIK-1 expressed in HEK293 cells. As reported earlier, whole-cell THIK-1 current was inhibited by halothane and activated by arachidonic acid. Among 25 additional modulators tested, bupivacaine (100 μM), quinidine (50 μM) and Ba(2+) (3 mM) and cold (10 °C) were most effective inhibitors of THIK-1 current (>50 % inhibition). In cell-attached patches with high KCl in the pipette and bath solutions, THIK-1 produced a small-conductance (~5 pS) channel with a weak inwardly rectifying current-voltage relationship. Halothane, bupivacaine and cold inhibited the single-channel activities of both THIK-1 and the 5-pS channel in TG neurons, whereas arachidonic acid augmented them. THIK-1 expressed in HEK293 cells and the 5-pS channels in TG neurons were insensitive to hypoxia. Reverse transcriptase-PCR, Western blot and immunocytochemical analyses suggested that THIK-1 mRNA and protein were expressed in TG neurons. These results show that THIK-1 is functionally expressed in TG neurons and contributes to the background K(+) conductance.

Characterization of distinct single-channel properties of Ca2+ inward currents in mitochondria

Previous studies have demonstrated several molecularly distinct players involved in mitochondrial Ca2+ uptake. In the present study, electrophysiological recordings on mitoplasts that were isolated from HeLa cells were performed in order to biophysically and pharmacologically characterize Ca2+ currents across the inner mitochondrial membrane. In mitoplast-attached configuration with 105 mM Ca2+ as a charge carrier, three distinct channel conductances of 11, 23, and 80 pS were observed. All types of mitochondrial currents were voltage-dependent and essentially depended on the presence of Ca2+ in the pipette. The 23 pS channel exhibited burst kinetics. Though all channels were sensitive to ruthenium red, their sensitivity was different. The 11 and 23 pS channels exhibited a lower sensitivity to ruthenium red than the 80 pS channel. The activities of all channels persisted in the presence of cylosporin A, CGP 37187, various K+-channel inhibitors, and Cl− channel blockers disodium 4,4′-diisothiocyanatostilbene-2,2′-disulfonate and niflumic acid. Collectively, our data identified multiple conductances of Ca2+ currents in mitoplasts isolated from HeLa cells, thus challenging the dogma of only one unique mitochondrial Ca2+ uniporter.

ATP signaling is deficient in cultured pannexin1‐null mouse astrocytes

Pannexins (Panx1, 2, and 3) comprise a group of proteins expressed in vertebrates that share weak yet significant sequence homology with the invertebrate gap junction proteins, the innexins. In contrast to the other vertebrate gap junction protein family (connexin), pannexins do not form intercellular channels, but at least Panx1 forms nonjunctional plasma membrane channels. Panx1 is ubiquitously expressed and has been shown to form large conductance (500 pS) channels that are voltage dependent, mechanosensitive, and permeable to relatively large molecules such as ATP. Pharmacological and knockdown approaches have indicated that Panx1 is the molecular substrate for the so-called "hemichannel" originally attributed to connexin43 and that Panx1 is the pore-forming unit of the P2X(7) receptor. Here, we describe, for the first time, conductance and permeability properties of Panx1-null astrocytes. The electrophysiological and fluorescence imaging analyses performed on these cells fully support our previous pharmacological and Panx1 knockdown studies that showed profoundly lower dye uptake and ATP release than wild-type untreated astrocytes. As a consequence of decreased ATP paracrine signaling, intercellular calcium wave spread is altered in Panx1-null astrocytes. Moreover, we found that in astrocytes as in Panx1-expressing oocytes, elevated extracellular K(+) activates Panx1 channels independently of membrane potential. Thus, on the basis of our present findings and our previous report, we propose that Panx1 channels serve as K(+) sensors for changes in the extracellular milieu such as those occurring under pathological conditions.

Single Channel Characterization of the Mitochondrial Ryanodine Receptor in Heart Mitoplasts

Heart mitochondria utilize multiple Ca(2+) transport mechanisms. Among them, the mitochondrial ryanodine receptor provides a fast Ca(2+) uptake pathway across the inner membrane to control "excitation and metabolism coupling." In the present study, we identified a novel ryanodine-sensitive channel in the native inner membrane of heart mitochondria and characterized its pharmacological and biophysical properties by directly patch clamping mitoplasts. Four distinct channel conductances of ∼100, ∼225, ∼700, and ∼1,000 picosiemens (pS) in symmetrical 150 mm CsCl were observed. The 225 pS cation-selective channel exhibited multiple subconductance states and was blocked by high concentrations of ryanodine and ruthenium red, known inhibitors of ryanodine receptors. Ryanodine exhibited a concentration-dependent modulation of this channel, with low concentrations stabilizing a subconductance state and high concentrations abolishing activity. The 100, 700, and 1,000 pS conductances exhibited different channel characteristics and were not inhibited by ryanodine. Taken together, these findings identified a novel 225 pS channel as the native mitochondrial ryanodine receptor channel activity in heart mitoplasts with biophysical and pharmacological properties that distinguish it from previously identified mitochondrial ion channels.

S-wave resonances in the positron–helium scattering

We have performed a three-body calculation for investigation of S-wave resonances in the positron–helium scattering in the hyperspherical coordinates. B-splines are used to obtain accurate hyperspherical potential curves and channel functions. An adiabatical hyperspherical approach is used to predict semi-quantitatively the position of the resonances. A multichannel calculation with the stabilization method is also used to extract accurately the positions and widths of resonances. We find four resonances associated with the He+–Ps(n = 2) channel. The resonance parameters for the lowest two resonances are in reasonable agreement with the calculations of Kar and Ho (2004 J. Phys. B: At. Mol. Opt. Phys. 37 3177), and two more new resonances below the Ps(n = 2) threshold are identified.

Outward Currents Through “low” Conductance Non-Mechanosensitive Channels in Escherichia Coli Membranes

Mechanosensitive high conductance channels in bacteria have received considerable attention (e.g.1,2) and have a presumed role against osmotic stress. In contrast non-mechanosensitive channels are less well described. In patch-clamp on-spheroplast recordings from E. coli (BW25113) with high K+ (200 mM) in both the pipette and bath solution MscL, MscK, MscS and MscM channels are reproducibly seen, and appear to be the only channels present. In on-spheroplast recordings with high Ca2+ or Mg2+ (100 mM) in the pipette and bath solution both MscL and MscM channels are observed. In addition, lower conductance channels of < 30 pS (n = 12) and 80 - 100 pS (n = 12) respectively are observed at depolarised potentials (pipette potential - 55 mV and above) in the absence of applied pressure in these solutions. These openings are long duration, non-flickery (in the case of the < 30 pS channel) and shorter duration, flickery (in the case of the 80-100 pS channel). The I-V relationships appear linear over a limited voltage range (pipette potentials −55 to −90 mV). The “low” conductance channels are seen in the absence of Cl- ions (sulphate as replacement) in the pipette and bath solutions. These channels are not seen in excised inside-out patches (n = 6). The identity, ionic selectivity and role of these channels remain to be characterised. An anion preferring 100 pS conductance channel in the absence of applied pressure has been reported previously in excised patches at both depolarised and hyperpolarised potentials in high K+ (150) solutions (3).1. Martinac, B. et al. PNAS, 84, 2297-2301 (1987)2. Booth, I.R. et al. Nature Rev. Microbiol., 5, 431-440 (2007).3. Kubalski, A. Biochim. et Biophys. Acta, 1238, 177-182 (1995)1CDC is supported by a Cardiff University Endowment Scholarship.

Convergent close-coupling calculations of positron scattering on metastable helium

The convergent close-coupling method has been applied to positron scattering on a helium atom in the 2 {sup 3}S metastable state. For this system the positronium (Ps) formation channel is open even at zero scattering energy making the inclusion of the Ps channels especially important. Spin algebra is presented for the general case of arbitrary spins. A proof is given of the often-used assumption about the relationship between the amplitudes for ortho-positronium and para-positronium formation. The cross sections for scattering from 2 {sup 3}S are shown to be significantly larger than those obtained for the ground state.

Clustering of protein kinase A-dependent CFTR chloride channels in the sarcolemma of guinea-pig ventricular myocytes

Cardiac myocytes express protein kinase A-dependent Cl− (ClPKA) channels that are thought to represent cardiac expression of CFTR. In the present study, the ‘Smart’ patch clamp technique was used to investigate the distribution of ClPKA channels at the cell surface of isolated guinea-pig ventricular myocytes. Imaging the cell surface using scanning ion conductance microscopy allowed the identification of the mouths to t-tubules and lateral z-grooves with a spacing of 1.86μm. Cell-attached patch clamp recordings were made from specified locations within the imaged area. Perfusion of the cells with an activating cocktail of isoprenaline (5μM), forskolin (10μM) and isobutylmethylxanthine (50μM) activated large, noisy anion-selective currents in which unitary channel currents could not be identified. Currents were recorded both from within z-grooves and in the inter-groove region but not at the mouths of t-tubules. Power spectral and noise analyses indicated the involvement of 13.5pS channels occurring in clusters of >50 channels. Channel activity was lost on excision of the patch from the cell but could be recovered in inside-out excised patches by application of the catalytic subunit of PKA. These results suggest that CFTR ClPKA channels occur in clusters in the sarcolemma of guinea-pig ventricular myocytes; there was no evidence of a heterogeneous distribution of clusters between the z-grooves and the inter-groove region.

CYP-omega-hydroxylation-dependent metabolites of arachidonic acid inhibit the basolateral 10 pS chloride channel in the rat thick ascending limb

Metabolites of arachidonic acid influence sodium chloride (NaCl) transport in the thick ascending limb. Because a 10 pS Cl channel is the major type of chloride channel in the basolateral membrane of this nephron segment, we explored the effect of arachidonic acid on this channel in cell-attached patches. Addition of 5 micromol arachidonic acid significantly decreased channel activity (a product of channel number and open probability) while linoleic acid had no effect. To determine if this was mediated by acachidonic acid per se or by its metabolites, we measured channel activity in the presence of the cyclooxygenase inhibitor indomethacin, the selective lipoxygenase inhibitor nordihydroguaiaretic acid, and the cytochrome P-450 (CYP)-omega-hydroxylation inhibitor 17-octadecynoic acid. Neither cyclooxygenase nor lipoxygenase inhibition had an effect on basal chloride channel activity; further they failed to abolish the inhibitory effect of arachidonate on the 10 pS channel. However, inhibition of CYP-omega-hydroxylation completely abolished the effect of arachidonic acid. The similarity of the effects of 20-hydroxyeicosatetraenoic acid (20-HETE) and arachidonic acid suggests that the effect of arachidonic acid was mediated by CYP-omega-hydroxylation-dependent metabolites. We conclude that arachidonic acid inhibits the 10 pS chloride channel in the basolateral membrane of the medullary thick ascending limb, an effect mediated by the CYP-omega-hydroxylation-dependent metabolite 20-HETE.

Heteromeric TASK‐1/TASK‐3 is the major oxygen‐sensitive background K+ channel in rat carotid body glomus cells

Carotid body (CB) glomus cells from rat express a TASK-like background K+ channel that is believed to play a critical role in the regulation of excitability and hypoxia-induced increase in respiration. Here we studied the kinetic behaviour of single channel openings from rat CB cells to determine the molecular identity of the 'TASK-like' K+ channels. In outside-out patches, the TASK-like background K+ channel in CB cells was inhibited >90% by a reduction of pH(o) from 7.3 to 5.8. In cell-attached patches with 140 mM KCl and 1 mM Mg2+ in the bath and pipette solutions, two main open levels with conductance levels of approximately 14 pS and approximately 32 pS were recorded at a membrane potential of -60 mV. The K+ channels showed kinetic properties similar to TASK-1 (approximately 14 pS), TASK-3 (approximately 32 pS) and TASK-1/3 heteromer (approximately 32 pS). The presence of three TASK isoforms was tested by reducing [Mg2+](o) to approximately 0 mM, which had no effect on the conductance of TASK-1, but increased those of TASK-1/3 and TASK-3 to 42 pS and 74 pS, respectively. In CB cells, the reduction of [Mg2+](o) to approximately 0 mM also caused the appearance of approximately 42 pS (TASK-1/3-like) and approximately 74 pS (TASK-3-like) channels, in addition to the approximately 14 pS (TASK-1-like) channel. The 42 pS channel was the most abundant, contributing approximately 75% of the current produced by TASK-like channels. Ruthenium red (5 microM) had no effect on TASK-1 and TASK-1/3, but inhibited TASK-3 by 87%. In CB cells, ruthenium red caused approximately 12% inhibition of TASK-like activity. Methanandamide reduced the activity of all three TASKs by 80-90%, and that of TASK-like channels in CB cell also by approximately 80%. In CB cells, hypoxia caused inhibition of TASK-like channels, including TASK-1/3-like channels. These results show that TASK-1, TASK-1/3 and TASK-3 are all functionally expressed in isolated CB cells, and that the TASK-1/3 heteromer provides the major part of the oxygen-sensitive TASK-like background K+ conductance.

Novel channels of the inner mitochondrial membrane

Along with a large number of carriers, exchangers and “pumps”, the inner mitochondrial membrane contains ion-conducting channels which endow it with controlled permeability to small ions. Some have been shown to be the mitochondrial counterpart of channels present also in other cellular membranes. The manuscript summarizes the current state of knowledge on the major inner mitochondrial membrane channels, properties, identity and proposed functions. Considerable attention is currently being devoted to two K+-selective channels, mtKATP and mtBKCa. Their activation in “preconditioning” is considered by many to underlie the protection of myocytes and other cells against subsequent ischemic damage. We have recently shown that in apoptotic lymphocytes inner membrane mtKV1.3 interacts with the pro-apoptotic protein Bax after the latter has inserted into the outer mitochondrial membrane. Whether the just-discovered mtIKCa has similar cellular role(s) remains to be seen. The Ca2+ “uniporter” has been characterized electrophysiologically, but still awaits a molecular identity. Chloride-selective channels are represented by the 107 pS channel, the first mitochondrial channel to be observed by patch-clamp, and by a ∼400 pS pore we have recently been able to fully characterize in the inner membrane of mitochondria isolated from a colon tumour cell line. This we propose to represent a component of the Permeability Transition Pore. The available data exclude the previous tentative identification with porin, and indicate that it coincides instead with the still molecularly unidentified “maxi” chloride channel.