High-conductance Channel Research Articles

Clofilium inhibits Slick and Slack potassium channels

Slick and Slack high-conductance potassium channels have been recently discovered, and are found in the central nervous system and in the heart. Both channels are activated by Na+ and Cl−, and Slick channels are also inhibited by adenosine triphospate (ATP). An important role of setting the resting membrane potential and controlling the basal excitability of neurons has been suggested for these channels. In addition, no specific blockers for these channels are known up to the present. With the purpose of studying the pharmacological characteristics of Slick and Slack channels, the effects of exposure to the antiarrhythmic compound clofilium were evaluated. Clofilium was able to modulate the activity of Slick and Slack channels effectively, with a stronger effect on Slack than Slick channels. In order to evaluate the pharmacological behavior of Slick and Slack channels further, 38 commonly used potassium channel blockers were tested. Screening of these compounds did not reveal any modulators of Slick and Slack channels, except for clofilium. The present study provides a first approach towards elucidating the pharmacological characteristics of Slick and Slack channels and could be the basis for future studies aimed at developing potent and specific blockers and activators for these channels.

Mineralocorticoids participate in the reduced vascular reactivity of pregnant rats

The renin-angiotensin-aldosterone (RAA) system is markedly activated in pregnancy. We evaluated if mineralocorticoid receptors (MR), a major component of the RAA system, are involved in the reduced vascular reactivity associated with pregnancy. Canrenoate (MR antagonist; 20 mg·kg(-1)·day(-1)) was administered to nonpregnant (NP) rats for 7 days and to pregnant rats from day 15 to 22 of gestation. These were killed on day 17, 19, or 22 of gestation and, for NP rats, after 7 days treatment. Constrictor responses to phenylephrine (PhE) and KCl were measured in endothelium-denuded thoracic aortic rings under the influence of modulators of potassium (activators) and calcium (blocker) channels. Responses to the constrictors were blunted from days 17 to 22 of gestation. Although canrenoate increased responses to PhE and KCl, it did not reverse their blunted responses in gestation. NS-1619 and cromakalim (respectively, high-conductance calcium-activated potassium channels and ATP-sensitive potassium channel activators) diminished responses to both PhE and KCl. Inhibition by NS-1619 on responses to both agonists was decreased under canrenoate treatment in NP, but the reduced influence of NS-1619 during gestation was reversed by the mineralocorticoid antagonist. Cromakalim reduced the response to PhE significantly in the pregnant groups; this effect was enhanced by canrenoate. Finally, nifedipine (calcium channel blocker) markedly reduced KCl responses but to a lesser extent at the end of pregnancy, an inhibiting effect that was increased with canrenoate treatment. These data demonstrate that treating rats with a MR antagonist increased vascular reactivity but that it differentially affected potassium and calcium channel activity in aortas of NP and pregnant animals. This suggests that aldosterone is one of the components involved in vascular adaptations to pregnancy.

Maxi-channels recorded in situ from ICC and pericytes associated with the mouse myenteric plexus

Ion channels are fundamental to gastrointestinal pacemaking by interstitial cells of Cajal (ICC). Previously, we have recorded a high-conductance chloride channel (HCCC) from ICC, both in culture and in situ, associated with the myenteric plexus. The biophysical properties of the HCCC (conductance, subconductances, voltage- and time-dependent inactivation) suggest it is a member of a class called the maxi-anion channels. In this study we further investigated the properties of the HCCC in situ. Our main finding was that the HCCC is not strictly a chloride channel but has a relative sodium-chloride permeability (P(Na/Cl)) of 0.76 to 1.64 (depending on the method of measurement). Therefore, we have renamed the HCCC the "maxi-channel." A maxi-channel was also expressed by pericytes associated with the vasculature near the myenteric plexus. This had a lower P(Na/Cl) (0.33 to 0.49, depending on the method of measurement) but similar conductance (326 ± 7 vs. 316 ± 24 pS for ICC). This is the first report of cation permeability equaling anion permeability in a maxi-anion channel. As such, the properties of the maxi-channels described in this article may have implications for the maxi-anion channel field, as well as for studies of their role in ICC and pericytes.

Single Cysteines in the Extracellular and Transmembrane Regions Modulate Pannexin 1 Channel Function

Pannexins form high-conductance ion channels in the membranes of many vertebrate cells. Functionally, they have been associated with multiple functional pathways like the propagation of calcium waves, ATP release, responses to ischemic conditions and apoptosis. In contrast to accumulating details which uncovered their functions, the molecular mechanisms for pannexin channel regulation and activation are hardly understood. To further elucidate regulatory mechanisms, we substituted cysteine residues, expected key elements for channel function, in extracellular and transmembrane regions of Pannexin 1 (Panx1). Most apparently, substitution of the transmembrane cysteine C40 resulted in constitutively open channels with profoundly increased activity. Hence, Xenopus laevis oocytes injected with corresponding cRNA showed strongly impaired viability, anomalous dye uptake and greatly increased whole-cell conductivity. All changes induced by C40 substitution were significantly reduced by the Panx1 channel blocker carbenoxolone, indicating that channel activity of the mutated Panx1 had been affected. In contrast, no changes occurred after substitution of the two other transmembrane cysteines, C215 and C227, in terms of channel conductivity. Finally, substitution of any of the four extracellular cysteines resulted in complete loss of channel function in both X. laevis oocytes and transfected N2A cells. From this, we conclude that cysteine residues of Panx1 reveal differential functional profiles for channel activation and drug sensitivity.

A type of voltage-dependent Ca2+ channel on Vicia faba guard cell plasma membrane outwardly permeates K+

The fine regulation of stomatal aperture is important for both plant photosynthesis and transpiration, while stomatal closing is an essential plant response to biotic and abiotic stresses such as drought, salinity, wounding, and pathogens. Quick stomatal closing is primarily due to rapid solute loss. Cytosolic free calcium ([Ca(2+)](cyt)) is a ubiquitous second messenger, and its elevation or oscillation plays important roles in stomatal movements, which can be triggered by the opening of Ca(2+)-permeable channels on the plasma membrane. For Ca(2+)-permeable channel recordings, Ba(2+) is preferred as a charge-carrying ion because it has higher permeability to Ca(2+) channels and blocks K(+) channel activities to facilitate current recordings; however, it prevents visualization of Ca(2+) channels' K(+) permeability. Here, we employed Ca(2+) instead of Ba(2+) in recording Ca(2+)-permeable channels on Vicia faba guard cell plasma membrane to mimic physiological solute conditions inside guard cells more accurately. Inward Ca(2+) currents could be recorded at the single-channel level, and these currents could be inhibited by micromolar Gd(3+), but their reversal potential is far away from the theoretical equilibrium potential for Ca(2+). Further experiments showed that the discrepancy of the reversal potential of the recorded Ca(2+) currents is influenced by cytosolic K(+). This suggests that voltage-dependent Ca(2+) channels also mediate K(+) efflux at depolarization voltages. In addition, a new kind of high-conductance channels with fivefold to normal Ca(2+) channel and 18-fold to normal outward K(+) conductance was found. Our data presented here suggest that plants have their own saving strategies in their rapid response to stress stimuli, and multiple kinds of hyperpolarization-activated Ca(2+)-permeable channels coexist on plasma membranes.

Effect of subauroral polarization streams on the thermosphere: A statistical study

Using 2 years of coordinated CHAMP and DMSP observations we have investigated for the first time the relationship between subauroral polarization streams (SAPS), ionospheric Hall current (electrojet), upper thermospheric zonal wind, and mass density at subauroral regions in the dusk and premidnight sectors, separately for both hemispheres. For comparison, we have also analyzed the same parameters as a function of magnetic latitude (30 degrees-80 degrees magnetic latitude) during non-SAPS periods. During periods of non-SAPS, the neutral wind exhibits similar features as during SAPS events in the dusk to premidnight sector, streaming westward in the same direction as the plasma drift. Both neutral and plasma velocities peak at the same latitude regardless of SAPS occurrence. For higher geomagnetic activity both velocities are faster and the peaks shift equatorward. During non-SAPS periods, the ratio between plasma and neutral wind velocity is on average 2.75 +/- 0.4 in both hemispheres irrespective of geomagnetic activity. The neutral wind during SAPS events gets enhanced by a factor of 1.5/1.2 for Kp = 4 in the Northern/Southern Hemisphere, respectively, as compared to non-SAPS time. The velocity difference between SAPS and neutral wind is also larger during SAPS period than during non-SAPS period, and the difference tends to increase with increasing geomagnetic activity. The peak latitude of the eastward auroral electrojet appears 1.5 degrees poleward of the plasma drift during SAPS events, confirming the formation of SAPS equatorward of the high-conductivity channel. These SAPS-induced large winds can heat the upper thermosphere. As a result we observe a 10% enhanced mass density at 400 km altitude with respect to periods without SAPS. In addition a density anomaly peak occurs collocated with the SAPS, displaced from the electrojet peak. We regard this as an indication for efficient thermospheric heating by ion neutral friction.

The Effects of Idebenone on Mitochondrial and Cellular Bioenergetics

Idebenone [2,3-dimethoxy-5-methyl-6(10-hydroxydecyl)-1,4-benzoquinone] is a synthetic short-chain analogue of coenzyme Q10 (CoQ10). A variety of quinones (including idebenone) have also been shown to affect the mitochondrial permeability transition pore (PTP), a high-conductance inner membrane channel modulated by the proton electrochemical gradient and by many signaling molecules. The PTP links oxidative stress to cell death, and may be involved in the pathogenesis of Leber's hereditary optic neuropathy (LHON) and possibly to other conditions with complex I deficiency. Given these complex effects of idebenone, we have investigated its effects on bioenergetics and PTP modulation in intact cells. Our results indicate that: (i) idebenone promotes CsA-sensitive opening of the PTP and subsequent loss of pyridine nucleotides; (ii) dithiothreitol prevents PTP opening and its detrimental consequences; (iii) idebenol does not cause PTP opening, and stimulates electron transfer at complex III of the respiratory chain; and (iv) idebenol-stimulated respiration is coupled to ATP synthesis both in rotenone-treated normal cells and in RJ206 cells (harboring the 3460/ND1 LHON mutation) and XTC.UC1 thyroid oncocytoma cells (bearing a disruptive frameshift mutation in the MT-ND1 gene, which impairs complex I assembly). Thus, under proper experimental conditions idebenol, can be a useful tool to bypass complex I defiencies.

C. Elegans Slo-2b uses its RCK1 Domain as a Ca 2+ Sensor and does not Exhibit Cl - Dependence

Slo-2 channels play an important role in the adaption of neuronal firing rates and have been implicated in protection against ischemia. Slo-2 channels belong to the family of high-conductance potassium channels but their gating mechanism is unique and has been reported to exhibit species differences. The rat Slo2 (Slack) channel is activated by Na+ and Cl-, whereas the C.elegans Slo-2a has been reported to be sensitive to Ca2+ and Cl-. Here, we report isolation of a novel isoform of the C. elegans channel Slo-2b (F08b12.3c) that was cloned from ESTs (YK1522e1, YK1193) of C.elegans, which has a distinct N-terminal region (by 18 amino acids) compared to the previously reported Slo-2a (F08b12.3b) (Yuan et al, 2000).

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.

Analyses of gating thermodynamics and effects of deletions in the mechanosensitive channel TREK-1

TREK-1, a mechanosensitive K channel from the two-pore family (K2P), is involved in protective regulation of the resting potential in CNS neurons and other tissues. The structure of TREK-1 and the basis of its sensitivity to stretch and variety of lipid-soluble factors remain unknown. Using existing K channel structures as modeling templates, TREK-1 was envisioned as a two-fold symmetrical complex with the gate formed primarily by the centrally positioned TM2b helices of the second homologous repeat. Opening was modeled as a conical expansion of the barrel separating TM2b’s accompanied by extension of TM2a helices with the cytoplasmic TM2a-TM1b connector. Seeking first experimental support to the models we have accomplished thermodynamic analysis of mouse TREK-1 gating and functional testing of several deletion mutants. The predicted increase of the channel in-plane area (ΔA) of ~5 nm2 in models was supported by the experimental ΔA of ~4 nm2 derived from the slope of open probability versus membrane tension in HEK-293T cells and their cytoskeleton-depleted blebs. In response to steps of suction, wild-type channel produced transient currents in cell-attached patches and mostly sustained currents upon patch excision. TREK-1 motifs not present in canonical K channels include divergent cytoplasmic N- and C-termini, and a characteristic 50-residue extracellular loop in the first homologous repeat. Deletion of the extracellular loop (Δ76–124) reduced the average current density in patches, increased spontaneous activity and generated a larger sub-population of high-conductance channels, while activation by tension augmented by arachidonic acid was fully retained. Further deletion of the C-terminal end (Δ76–124/Δ334–411) removed voltage dependency but otherwise produced no additional effect. In an attempt to generate a cysteine-free version of the channel, we mutated two remaining cysteines 159 and 219 in the transmembrane region. C219A did not compromise channel activity, whereas the C159A/S mutants were essentially inactive. Treatment with β-mercaptoethanol suggested that none of these cysteines form functionally-important disulfides.

Identification and Characterization of High-Conductive Layers in Waterfloods

Summary This study expands upon the use of modified-Hall analysis (MHA) to discern the characteristics of a high-permeability channel. Briefly, the modified-Hall plot uses three curves involving improved Hall-integral (H-I) and the two derivatives, analytic and numeric. Ordinarily, the derivative curves overlay on the integral curve during matrix injection, but separate lower when fracturing occurs. This work presents a method to identify and characterize high-conductive layers or channels between injector and producer pairs with the MHA. The distance separating the integral and derivative curves provides the required information to quantify channel properties. A simple analytical solution is presented for transforming the separation distance into channel permeabilitythickness product. The analytic derivative is based on the radial-flow-pattern assumption and the numeric derivative is correlated to the pressure response. Therefore, a comparison of these two curves reveals clues about the maturity of a waterflood at a given time. Several simulated examples verified the channel-property-estimation algorithm and identified the distinctive derivative signatures for channeling and fracturing situations. This method is also useful for identification of wormhole propagation during sand production in unconsolidated formations.

High conductive gate leakage current channels induced by In segregation around screw- and mixed-type threading dislocations in lattice-matched InxAl1−xN/GaN heterostructures

A correlation between microstructures and high gate leakage current density of Schottky contacts on lattice-matched InxAl1−xN/GaN heterostructures has been investigated by means of current-voltage measurements, conductive atom force microscopy (C-AFM), and transmission electron microscopy (TEM) investigations. It is shown that the reverse-bias gate leakage current density of Ni/Au Schottky contacts on InxAl1−xN/GaN heterostructures is more than two orders of magnitude larger than that on AlxGa1−xN/GaN ones. C-AFM and TEM observations indicate that screw- and mixed-type threading dislocations (S/M-TDs) are efficient leakage current channels in InxAl1−xN barrier and In segregation is formed around S/M-TDs. It is believed that In segregation around S/M-TDs reduces local Schottky barrier height to form conductive channels and leads to high leakage current density of Schottky contacts on InxAl1−xN/GaN heterostructures.

Optical studies of degradation of AlGaN quantum well based deep ultraviolet light emitting diodes

Aging under high current stress of AlGaN quantum well based light emitting diodes with high and low Al content in the wells emitting at 270 nm and 335 nm, respectively, has been studied by scanning near field optical spectroscopy and far field electroluminescence, photoluminescence and time-resolved photoluminescence. In the high Al content devices emission band related to optical transitions in the cladding involving nitrogen vacancies has been found. Evolution of this band during aging suggests that the role of N vacancies is crucial in the aging process by aiding defect generation and formation of high conductivity channels.

The role of STIM1 in the receptor- and store-operated calcium influx in HEK293 cells

The possible role of STIM1 protein in the regulation of activity of receptor- and store-operated Ca2+ channels in non-excitable cells has been studied. Receptor- and store-operated Ca2+ influxes have been measured using the fluorescent method of detection of cytosolic Ca2+ concentration and the electrophysiological methods of whole-cell and single-channel current recordings in the control HEK293 cells and in HEK293 cells with suppressed expression of STIM1. The experiments have shown that STIM1 suppression results in a reduction of the amplitudes of both receptor- and store-operated inward calcium currents. The decrease of total Ca2+ influx of in response to an agonist or to passive depletion of calcium stores upon STIM1 suppression was due to the decrease or total absence of the activity of high-conductance channels Imax and non-selective channels Ins in HEK293 cells. A decrease in the STIM1 amount also altered the activity regulation of low-conductance Imin channels that changed from exclusively agonist-operated into store-dependent channels in HEK293 cells.

A high-conductance cation channel from the inner membrane of the free-living soil bacteria Rhizobium etli

In this communication we reported the study of a cation channel present in the cytoplasmic membrane of the nitrogen fixing bacterium Rhizobium etli. Inner-membrane (IM) vesicles were purified and fused into planar lipid bilayers (PLBs), under voltage clamp conditions. We have found that fusion of IM-enriched vesicle fractions with these model membranes leads, mainly (>30% of 46 experiments), to the reconstitution of high-conductance channels. Following this strategy, the activity of a channel with main open conductance of 198 pS, in symmetrical 100 mM KCl, was recorded. The single-channel conductance increase to 653 pS in the presence of a 5:1 (cis to trans) gradient of KCl. The channel exhibits voltage dependency and a weak selectivity for cations showing a permeability ratios of P (Rb)/P (K) = 0.96, P (Na)/P (K) = 0.07, and a conductance ratio of gamma(Rb)/gamma(K) = 1.1. The channel here characterized represents a previously undescribed Rhizobium channel although its precise role in rhizobial physiology remains yet to be determined.

Crustal deformation of the eastern Tibetan plateau revealed by magnetotelluric imaging

The ongoing collision of the Indian and Asian continents has created the Himalaya and Tibetan plateau through a range of deformation processes. These include crustal thickening, detachment of the lower lithosphere from the plate (delamination) and flow in a weakened lower crust 1‐6 . Debate continues as to which of these processes are most significant 7 . In eastern Tibet, large-scale motion of the surface occurs, but the nature of deformation at depth remains unresolved. A large-scale crustal flow channel has been proposed as an explanation for regional uplift in eastern Tibet 6,8,9 , but existing geophysical data 10,11 do not constrain the pattern of flow. Magnetotellurics uses naturally occurring electromagnetic waves to image the Earth’s subsurface. Here we present magnetotelluric data that image two major zones or channels of high electrical conductivity at a depth of 20-40 km. The channels extend horizontally more than 800 km from the Tibetan plateau into southwest China. The electrical properties of the channels imply an elevated fluid content consistent with a weak crust 12,13 that permits flow on a geological timescale. These findings support the hypothesis that crustal flow can occur in orogenic belts and contribute to uplift of plateaux. Our results reveal the previously unknown complexities of these patterns of crustal flow. Many previous studies of the IndiaAsia

Characterization of a stretch‐activated potassium channel in chondrocytes

Chondrocytes possess the capacity to transduce load-induced mechanical stimuli into electrochemical signals. The aim of this study was to functionally characterize an ion channel activated in response to membrane stretch in isolated primary equine chondrocytes. We used patch-clamp electrophysiology to functionally characterize this channel and immunohistochemistry to examine its distribution in articular cartilage. In cell-attached patch experiments, the application of negative pressures to the patch pipette (in the range of 20–200 mmHg) activated ion channel currents in six of seven patches. The mean activated current was 45.9 ± 1.1 pA (n = 4) at a membrane potential of 33 mV (cell surface area approximately 240 µm2). The mean slope conductance of the principal single channels resolved within the total stretch-activated current was 118 ± 19 pS (n = 6), and reversed near the theoretical potassium equilibrium potential, EK+, suggesting it was a high-conductance potassium channel. Activation of these high-conductance potassium channels was inhibited by extracellular TEA (Kd approx. 900 µM) and iberiotoxin (Kd approx. 40 nM). This suggests that the current was largely carried by BK-like potassium (MaxiK) channels. To further characterize these BK-like channels, we used inside-out patches of chondrocyte membrane: we found these channels to be activated by elevation in bath calcium concentration. Immunohistochemical staining of equine cartilage samples with polyclonal antibodies to the α1- and β1-subunits of the BK channel revealed positive immunoreactivity for both subunits in superficial zone chondrocytes. These experiments support the hypothesis that functional BK channels are present in chondrocytes and may be involved in mechanotransduction and chemotransduction.

Domain Decomposition Preconditioners for Multiscale Flows in High Contrast Media: Reduced Dimension Coarse Spaces

In this paper, robust preconditioners for multiscale flow problems are investigated. We consider elliptic equations with highly varying coefficients. We design and analyze two-level domain decomposition preconditioners that converge independent of the contrast in the media properties. The coarse spaces are constructed using selected eigenvectors of a local spectral problem. Our new construction enriches any given initial coarse space to make it suitable for high-contrast problems. Using the initial coarse space we construct local mass matrices for the local eigenvalue problems. We show that there is a gap in the spectrum of the eigenvalue problem when high-conductivity regions are disconnected. The eigenvectors corresponding to small, asymptotically vanishing eigenvalues are chosen to construct an enrichment of the initial coarse space. Only via a judicious choice of the initial space do we reduce the dimension of the resulting coarse space. Classical coarse basis functions such as multiscale or energy minimizing basis functions can be taken as the basis for the initial coarse space. In particular, if we start with classical multiscale basis, the selected eigenvectors represent only high-conductivity features that cannot be localized within a coarse-grid block, e.g., high-conductivity channels that connect the boundaries of a coarse-grid block. Numerical experiments are presented. The new construction presented here can handle tensor coefficients. The results of this paper substantially extend those presented in [J. Galvis and Y. Efendiev, Multiscale Model. Simul., 8 (2010), pp. 1461–1483], where only scalar coefficients are considered and the coarse space dimension can be very large because the coarse space includes all isolated high-conductivity features that are within a coarse block.

Mechanism for Strict Regulation of Certain K+ Channels by Small, Fast Changes in Cell Volume

A number of physiological processes, such as salt and water transport, neuronal activity, migration and apoptosis, involve changes in cell volume. The response of the cells to such challenges often is a regulatory volume decrease (RVD), a mechanism which involves activation of K+ channels. However, so far it has not been entirely clear which types of K+ channels should be considered sensitive to cell volume changes and, in particular, the mechanism for regulation has been obscure. To address this issue, we have co-expressed a number of K+ channels with aquaporins in Xenopus laevis oocytes and subsequently induced changes in cell voume by exposure to hypo- or hypertonic media. In all cases, the results are very clear; some K+ channels (e.g. KCNQ1 and 4, Kir4.1/5.1, Ca2+-activated IK and SK) are strictly regulated by small, fast changes in cell volume (approx. 5 %), whereas others are not (e.g. KCNQ2/3, Slo1 (BK) and Slo2.2 (slack)). Most recently, we have shown that the high-conductance slick channel (Slo 2.1) is dramatically stimulated (to 196 % of control) by cell swelling and inhibited (to 44 % of control) by a decrease in cell volume. Our results show that the mechanism responsible for the strict regulation of certain K+ channels by small, fast changes in cell volume, in some cases, involve the cytoskeleton.In contrast, cellular release of ATP is not involved, and the regulation is not mediated by membrane stretch. Our recent finding, that the high conductance slick channel is highly cell volume sensitive, will allow for further investigations at a single channel level.

Aging Results in Downregulation of Putative Components of mPTP in Human Atria

Cardiac vulnerability to injury is increased with aging and is associated with enhanced susceptibility to opening of mitochondrial permeability transition pore (mPTP), a nonspecific high conductance channel in the inner mitochondrial membrane, however the basis for this is not fully understood. The effect of aging on the expression of putative components of mPTP in human myocardium was determined in atrial tissue obtained from elderly (76±6 yrs) and adult (49±5 yrs) patients undergoing coronary artery bypass surgery using microarray, Quantitative RT-PCR and Western blot. Aging was associated with a significant reduction in the expression of genes coding for the voltage-dependent anion channel isoforms, VDAC1, VDAC2 and VDAC3, adenine nucleotide translocase (ANT) and Cyclophilin-D (PPID) in atria from the elderly patients (Fig A, p<0.01). The expression of VDAC1 and ANT proteins was significantly reduced (p<0.05), while VDAC2, VDAC3 and cyclophillin D were not significantly altered at protein level (Fig B). Downregulation of VDAC1 and ANT expression in the aging human heart may underlie the increased predisposition of the atria to injury during stress.