The Na/K pump,resting potential and selective permeability in canine Purkinje fibres at physiologic and room temperatures

All mammalian cells maintain a resting potential generated by ions moving down concentration gradients. In excitable cells, the inside potential is negative relative to outside. In order to maintain this electrochemical gradient, the sodium potassium (Na/K) pump actively transports out three sodium ions for every two potassium ions it brings in. This process generates a net outward current and thus hyperpolaizes the resting potential. I employed dihydroouabain (DHO) to inhibit the Na/K pump and thus measure its contribution to the resting potential. It contributed 9.0 mV at 34°C and 3.8 mV at 25°C. The P_K/P_Na ratios were calculated at both temperatures before and after subtracting the Na/K pump contribution. These ratios also suggested a decreased contribution of the Na/K pump under hypothermia. Taken together, these results suggest that the pump contribution to the resting potential is more significant at physiologic temperatures (34°C) than at room temperature (25°C), and that estimates of selective permeability can only be accurately obtained after assessing and eliminating the Na/K pump contribution to the resting potential.     

Die Wirkung der Sulfationen auf das Membranpotential der isoliert durchströmten Säugetiermuskulatur

Summary Electrical potential measurements of membrane resting and action potentials were made by means of electrolyte-filled glass micro-electrodes on single fibres of the musculus gracilis of the cat using a perfused hind-limb preparationin situ. The release of potassium from muscle and the tension developed by the gastrocnemius muscle were simultaneously recorded. The normal resting potential in our series was 91.7 mV (s.d. ± 6.7 mV). Partial replacement of the chloride by sulfate in the perfusion fluid led to (a) potassium release from the perfused hind-limb, (b) reversible contracture of the gastrocnemius muscle, (c) depression of the membrane resting potential which was proportional to the degree of replacement of chloride by sulfate in the perfusion fluid and (d) to the occurrence of volleys of spontaneous fibrillation potentials some of which had the shape of damped oscillations. These findings are similar to those observed after treatment with veratrine and are interpreted to be due to (1) increase in sodium permeability and (2) disturbance of the Donnan equilibrium for chloride ions.     

Cardiac cellular electrophysiology: past and present

Summary The time-course of the cardiac action potential can be accounted for in terms of ionic currents crossing the cell membranes. Depolarizing current is carried by Na⁺ or Ca²⁺ entering the cells, repolarizing current by K⁺ leaving the cells. Membrane permeability for the passive movement of these ions is thought to be voltage-dependent as well as time-dependent. Net transfer of charge may also result from active transport, 2 Na⁺ out against 1 K⁺ in; or coupled exchange, 3 or 4 Na⁺ in against 1 Ca²⁺ out. This review follows the path by which present-day knowledge has been reached. It also gives a few examples to illustrate that electrophysiology has provided concepts useful to clinical cardiology.     

Ionic mechanisms in pancreatic β cell signaling

The function and survival of pancreatic β cells critically rely on complex electrical signaling systems composed of a series of ionic events, namely fluxes of K⁺, Na⁺, Ca²⁺ and Cl^? across the β cell membranes. These electrical signaling systems not only sense events occurring in the extracellular space and intracellular milieu of pancreatic islet cells, but also control different β cell activities, most notably glucose-stimulated insulin secretion. Three major ion fluxes including K⁺ efflux through ATP-sensitive K⁺ (K_ATP) channels, the voltage-gated Ca²⁺ (Ca_V) channel-mediated Ca²⁺ influx and K⁺ efflux through voltage-gated K⁺ (K_V) channels operate in the β cell. These ion fluxes set the resting membrane potential and the shape, rate and pattern of firing of action potentials under different metabolic conditions. The K_ATP channel-mediated K⁺ efflux determines the resting membrane potential and keeps the excitability of the β cell at low levels. Ca²⁺ influx through Ca_V1 channels, a major type of β cell Ca_V channels, causes the upstroke or depolarization phase of the action potential and regulates a wide range of β cell functions including the most elementary β cell function, insulin secretion. K⁺ efflux mediated by K_V2.1 delayed rectifier K⁺ channels, a predominant form of β cell K_V channels, brings about the downstroke or repolarization phase of the action potential, which acts as a brake for insulin secretion owing to shutting down the Ca_V channel-mediated Ca²⁺ entry. These three ion channel-mediated ion fluxes are the most important ionic events in β cell signaling. This review concisely discusses various ionic mechanisms in β cell signaling and highlights K_ATP channel-, Ca_V1 channel- and K_V2.1 channel-mediated ion fluxes.     

Experimentelle Feststellung dualer Potentiale an intra-nicht-permutierenden Membranen

Summary It has been shown experimentally that two different potentials appear across an intra-nonpermutating membrane³ when two different solutions (e.g., solution I: 0.1n NaCl+0.0001n KCl; and, solution II: 0.1n KCl + 0.0001n NaCl) are separated by such a membrane, and when the pores of the intra-nonpermutating membrane are supplied with ions from either solution I or solution II (in this case: essentially with Na⁺ ions from solution I, or essentially with K⁺ ions from solution II). The theoretical background, and other considerations, for these experiments will be found in reference.     

Réversibilité de la réponse du potentiel de membrane chezNitella flexilis L. à des variations de pH

Summary The better the recovering of the membrane potential ofNitella on restoring the initial value of the external pH after a change, the more acid is the pH of the medium (Table I). On the other hand, a better repeatability was observed in alkaline solutions (Table II) for a change in the external K⁺ concentration. These results are interpreted as a manifestation of the binding of K⁺ ions to ionizable fixed charges (pK about 5–6) at the membrane surface and of the control of molecular structure of the membrane by the pH.     

The effects of triaminopyrimidine on the short circuit current and transmembrane potentials of the isolated rat visceral yolk sac in vitro

Summary Intracellular potentials in the cells from 17.5-day old rat visceral yolk sacs were measured by a glass microelectrode. When penetrated from the maternal side, the cells have potentials of about 50.2±1.9 mV (inside negative) which were reduced by increasing the external K⁺ concentration and increased by removing Na⁺ ions from the bathing fluid. Triaminopyrimidine (TAP) which inhibited Na⁺ transport caused a dose-dependent depolarization of the cell membrane. The depolarization was dependent on the presence of extracellular Ca²⁺ ions. It is proposed that TAP may inhibit Na⁺ transport by increasing the intracellular concentration of calcium ions.This work was supported by the University of Hong Kong (grant number 335. 034.5105).Acknowledgment. Triaminopyrimidine was synthesized by Dr. Barbara Roth of the Wellcome Research Laboratories.     

Direct inhibition of phospholipid scrambling activity in erythrocytes by potassium ions

The exposure of phosphatidylserine (PS) at the cell surface plays a critical role in blood coagulation and serves as a macrophage recognition moiety for the engulfment of apoptotic cells. Previous observations have shown that a high extracellular [K⁺] and selective K⁺ channel blockers inhibit PS exposure in platelets and erythrocytes. Here we show that the rate of PS exposure in erythrocytes decreases by ~50% when the intracellular [K⁺] increases from 0 to physiological concentrations. Using resealed erythrocyte membranes, we further show that lipid scrambling is inducible by raising the intracellular [Ca²⁺] and that K⁺ ions have a direct inhibitory effect on this process. Lipid scrambling in resealed ghosts occurs in the absence of cell shrinkage and microvesicle formation, processes that are generally attributed to Ca²⁺-induced lipid scrambling in intact erythrocytes. Thus, opening of Ca²⁺-sensitive K⁺ channels causes loss of intracellular K⁺ that results in reduced intrinsic inhibitory effect of these ions on scramblase activity. Received 11 September 2008; received after revision 17 October 2008; accepted 27 October 2008     

The mesenchymoangioblast,mesodermal precursor for mesenchymal and endothelial cells

Mesenchymoangioblast (MB) is the earliest precursor for endothelial and mesenchymal cells originating from APLNR⁺PDGFRα⁺KDR⁺ mesoderm in human pluripotent stem cell cultures. MBs are identified based on their capacity to form FGF2-dependent compact spheroid colonies in a serum-free semisolid medium. MBs colonies are composed of PDGFRβ⁺CD271⁺EMCN⁺DLK1⁺CD73^? primitive mesenchymal cells which are generated through endothelial/angioblastic intermediates (cores) formed during first 3–4 days of clonogenic cultures. MB-derived primitive mesenchymal cells have potential to differentiate into mesenchymal stromal/stem cells (MSCs), pericytes, and smooth muscle cells. In this review, we summarize the specification and developmental potential of MBs, emphasize features that distinguish MBs from other mesenchymal progenitors described in the literature and discuss the value of these findings for identifying molecular pathways leading to MSC and vasculogenic cell specification, and developing cellular therapies using MB-derived progeny.     

Enhancement of barium- and cesium-induced adrenal catecholamine release by lidocaine

Summary Catecholamine release evoked from isolated perfused bovine adrenals by Ba⁺² or Cs⁺ is enhanced by lidocaine or by a calcium-free medium. The action of Cs⁺ therefore differs from that of K⁺ or Rb⁺ in adrenal medulla. Divalent and monovalent metallic cations of relatively large atomic weight like Ba⁺² and Cs⁺, probably penetrate the cell more easily than small highly charged ions and act intracellularly to cause adrenal catecholamine release. Local anesthetics and calcium-free media may allow greater influx of Ba⁺² and Cs⁺ into adrenomedullary cells.Acknowledgment. This work was supported by NIH, grant No. AM16153.     

Na+,K+-ATPase as a docking station: protein–protein complexes of the Na+,K+-ATPase

The Na⁺,K⁺-ATPase, or sodium pump, is well known for its role in ion transport across the plasma membrane of animal cells. It carries out the transport of Na⁺ ions out of the cell and of K⁺ ions into the cell and thus maintains electrolyte and fluid balance. In addition to the fundamental ion-pumping function of the Na⁺,K⁺-ATPase, recent work has suggested additional roles for Na⁺,K⁺-ATPase in signal transduction and biomembrane structure. Several signaling pathways have been found to involve Na⁺,K⁺-ATPase, which serves as a docking station for a fast-growing number of protein interaction partners. In this review, we focus on Na⁺,K⁺-ATPase as a signal transducer, but also briefly discuss other Na⁺,K⁺-ATPase protein–protein interactions, providing a comprehensive overview of the diverse signaling functions ascribed to this well-known enzyme.     

Vanadate: Non-selective inhibition of transepithelial transport of Na+, H+ and water

Summary In the isolated urinary bladder of the toad, 10^–5–10^–4M orthovanadate produces inhibition of the active transport of Na⁺ and H⁺ ions as well as of antidiuretic hormone-mediated osmotic flow of water. Since transport of H⁺ ions and osmotic water flow are not inhibited when (Na⁺+K⁺)-ATPase is inhibited by ouabain, biological actions of vanadate are not necessarily related to inhibition of (Na⁺+K⁺)-ATPase.This research was supported by grant AM-14915 from the National Institutes of Helath.     

Biological effects of lithium: Experimental analysis in plant cytokinesis

Summary The biological effects of lithium ions have been studied, using plant cytokinesis in onion root meristems as the experimental model. Lithium induces binucleate cells by inhibiting cell plate formation. Moreover, lithium and caffeine have additive effects on the induction of binucleate cells. Na⁺, K⁺, Ca⁺⁺ and Mg⁺⁺ antagonize lithium-induced inhibition of cytokinesis.     

Über den Einfluss von Desoxycorticosteron auf Kontraktur und Kaliumfreisetzung durch Acetylcholin an der innervierten und denervierten Skelettmuskulatur

Summary The release of potassium ions from striated muscle, and the changes in mechanical tension developed by the gastrocnemius muscle on intraarterial injection of ACh, were investigated by isolated perfusion of the hind limbs in cats. The reaction of the normal innervated and chronically denervated muscle in the same animal were compared before and during perfusion with 2·10^–4 M/l desoxycorticosterone glucoside (DCG). The following results were obtained: after perfusion with DCG no change in the spontaneous release of potassium ions occurred neither on the innervated nor on the denervated muscle. The potassium release following intra-arterial injections of various doses of ACh was significantly reduced on innervated and denervated muscle. On the denervated muscle there was also a considerable reduction of the height of contractures caused by ACh administration. The results make it probable that DCG acts by an inhibition of depolarisation in the same way asd-tubocurarine.     

Red blood cell glycolysis and potassium type in sheep

Summary Based on the observations made on human and dog red blood cells, it was recently proposed that the response of red cell glycolysis to variations in the levels of specific cations is an evolutionary adaptation in response to a specific cellular environment. We have now examined the effect of K⁺ and Na⁺ on the activity of pyruvate kinase (PK) in the red blood cells from 2 genetically different types of sheep high potassium (HK) and low potassium (LK). The results indicate that K⁺ stimulate glucose consumption and the activity of PK in both types of sheep. It thus appears that red cell PK from LK sheep does not fit into the concept of cellular environment and PK activity.This work was supported by grants from the National Health and Medical Research Council of Australia, the Clive and Vera Ramaciotti New South Wales Foundation and the Helena Rubenstein Foundation, Inc.     

May K+ ions stimulate the formation of cyclic AMP in the brain independently on their depolarizing action?

Summary The effect of potassium ions on the formation of adenosine 3,5-monophosphate (cAMP) in the rat cerebral cortex in vivo was studied under conditions where development of spreading depression had been blocked by pretreatment of the cerebral cortex by topically applied magnesium ions. A linear relationship between potassium concentrations applied to the cortical surface and levels of cAMP has been found. Moreover, potentiation of the K⁺-effect by magnesium ions has been observed.     

Involvement of Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>-ATPase and its inhibitors in HuR-mediated cytokine mRNA stabilization in lung epithelial cells

Increasing evidence demonstrates that Na⁺, K⁺-ATPase plays an important role in pulmonary inflammation, but the mechanism remains largely unknown. In this study, we used cardiotonic steroids as Na⁺, K⁺-ATPase inhibitors to explore the possible involvement of Na⁺, K⁺-ATPase in pulmonary epithelial inflammation. The results demonstrated that mice after ouabain inhalation developed cyclooxygenase-2-dependent acute lung inflammation. The in vitro experiments further confirmed that Na⁺, K⁺-ATPase inhibitors significantly stimulated cyclooxygenase-2 expression in lung epithelial cells of human or murine origin, the process of which was participated by multiple cis-elements and trans-acting factors. Most importantly, we first described here that Na⁺, K⁺-ATPase inhibitors could evoke a significant Hu antigen R nuclear export in lung epithelial cells, which stabilized cyclooxygenase-2 mRNA by binding with a proximal AU-rich element within its 3′-untranslated region. In conclusion, HuR-mediated mRNA stabilization opens new avenues in understanding the importance of Na⁺, K⁺-ATPase, as well as its inhibitors in inflammation.     

Adrenaline and the electrogenic sodium pump inRana catesbeiana sympathetic ganglion cells

Summary The effect of adrenaline on the Na⁺-pump in bullfrog (Rana catesbeiana) sympathetic ganglion cells was studied by use of electrophysiological methods. The rate of removal of excess Na⁺ injected into a ganglion cell was increased by adrenaline. The K⁺-activated hyperpolarization of cell membrane, which might be produced by an electrogenic Na⁺-pump, was also increased by adrenaline. These results suggested that adrenaline was able to accelerate the Na⁺-pump, possibly the electrogenic Na⁺-pump.     

Identification of Treg-like cells in <Emphasis Type="Italic">Tetraodon</Emphasis>: insight into the origin of regulatory T subsets during early vertebrate evolution

CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Treg cells) are critical for the maintenance of peripheral tolerance, and the suppression of autoimmune diseases and even tumors. Although Treg cells are well characterized in humans, little is known regarding their existence or occurrence in ancient vertebrates. In the present study, we report on the molecular and functional characterization of a Treg-like subset with the phenotype CD4-2⁺CD25-like⁺Foxp3-like⁺ from a pufferfish (Tetraodon nigroviridis) model. Functional studies showed that depletion of this subset produced an enhanced mixed lymphocyte reaction (MLR) and nonspecific cytotoxic cell (NCC) activity in vitro, as well as inflammation of the intestine in vivo. The data presented here will not only enrich the knowledge of fish immunology but will also be beneficial for a better cross-species understanding of the evolutionary history of the Treg family and Treg-mediated regulatory networks in cellular immunity.     

Identification of cancer stem cell-like cells from human epithelial ovarian carcinoma cell line

Cancer stem cells (CSCs) play an important role in the development, invasion, and drug resistance of carcinoma, but the exact phenotype and characteristics of ovarian CSCs are still disputable. In this study, we identified cancer stem cell-like cells (CSC-LCs) and investigated their characteristics from the ovarian adenocarcinoma cell line 3AO. Our results showed that CSC-LCs were enriched in sphere-forming test and highly expressed CD44⁺CD24⁻. The spheres and CD24⁻ cells possessed strong tumorigenic ability by transplantation into nonobese diabetic/severe combined immunodeficient mice. CD44⁺CD24⁻ cells expressed stem cell markers and differentiated to CD44⁺CD24⁺ cells by immunofluorescence assay and fluorescence-activated cell-sorting analysis. In vitro experiments verified that CD44⁺CD24⁻ cells were markedly resistant to carboplatin and paclitaxol. In conclusion, our study identifies the CD44⁺CD24⁻ phenotype, self-renewal, high tumorigenicity, differentiation potential, and drug resistance of ovarian CSC-LCs. Our findings may provide the evidence needed to explore a new strategy in the treatment of ovarian cancer.