Study of Na+ and Water Transport in the Pigeon and Chicken Kidney by Lithium Clearance Method under Conditions of Water and Salt Load: Regimes of Renal Net Reabsorption and Net Secretion of Li+

The water (intestinally) and salt (intravenously) loads of a sufficient intensity (about 120 ml water or 9 mmol NaCl per kg body mass) caused a reversible conversion (of duration of 30–40 min) in the renal Li transport, i.e., transition from net reabsorption of this ion (FE_Li = C_Li/GFR < 1) to its net secretion (FE_Li > 1), where C_Li—lithium clearance, GFR—glomerular filtration rate, ⁶⁵ZnDTPA clearance. Maximal values of the fractional lithium excretion (FE_Li) amounted to about 1.5 and 2.0 after the water and salt loads, respectively. A repeated salt load (4–5 NaCl injections by 9 mmol/kg at 20–40 min intervals) induced a long (2–3 h) net secretion of lithium in the chicken kidney. This regime of renal functioning was characterized by abundant urination (20–30 ml/kg/h) and a substantial increase of the Na⁺ concentration in blood plasma (from 138 ± 9 to 172 ± 10 mM, the mean ( standard deviation) and in urine (to 157 ± 19 mM). The data obtained were considered in terms of a hypothesis suggesting that the renal lithium secretion indicates the appearance of net water and Na⁺ secretion in the proximal tubule of the avian kidney in response to water and salt load. The fractional reabsorption of Na⁺ and water in the chicken kidney were calculated by means of lithium clearance during both the net reabsorption and the secretion of lithium in the kidney. In the former regime of renal functioning (FE_Li < 1), regardless of changes in lithium reabsorption (up to its complete cessation at FE_Li = 1), the kidney as a whole reabsorbs about 99% of filtered Na⁺, while distal reabsorption of this ion accounts for about 98%. The corresponding values for water reabsorption are about 96 and 92%, respectively. At FE_Li > 1, the fractional reabsorption of Na⁺ and water decrease significantly: the minimal values amount to about 60%, while the mean values, about 80%.     

Electrogenic properties of the sodium-alanine cotransporter in pancreatic acinar cells: II. Comparison with transport models

Summary In this paper, the results of the preceding electrophysiological study of sodium-alanine cotransport in pancreatic acinar cells are compared with kinetic models. Two different types of transport mechanisms are considered. In the simultaneous mechanism the cotransporterC forms a ternary complexNCS with Na⁺ and the substrateS; coupled transport of Na⁺ andS involves a conformational transition between statesNCS andNCS with inward- and outward-facing binding sites. In the consecutive (or ping-pong) mechanism, formation of a ternary complex is not required; coupled transport occurs by an alternating sequence of association-dissociation steps and conformational transitions. It is shown that the experimentally observed alanine- and sodium-concentration dependence of transport rates is consistent with the predictions of the simultaneous model, but incompatible with the consecutive mechanism. Assuming that the association-dissociation reactions are not rate-limiting, a number of kinetic parameters of the simultaneous model can be estimated from the experimental results. The equilibrium dissociation constants of Na⁺ and alanine at the extracellular side are determined to beK _N <-64mm andK _S <-18mm. Furthermore, the ratioK _N /K _N ^S of the dissociation constants of Na⁺ from the binary (NC) and the ternary complex (NCS) at the extracellular side is estimated to be <-6. This indicates that the binding sequence of Na⁺ andS to the transporter is not ordered. The current-voltage behavior of the transporter is analyzed in terms of charge translocations associated with the single-reaction steps. The observed voltage-dependence of the half-saturation concentration of sodium is consistent with the assumption that a Na⁺ ion that migrates from the extracellular medium to the binding site has to traverse part of the transmembrane voltage.     

Ionic permeation of lipid bilayer membranes mediated by a neutral,noncyclic Li+-selective carrier having imide and ether ligands. I. Selectivity among monovalent cations

Summary We have found that Simon's neutral, noncyclic, Li⁺-selective complexone, which has imide and ether ligands, renders lipid bilayer membranes selectively permeable to certain cations and anions. The present paper characterizes the ability of this molecule to carry monovalent cations; and we show it to be most selective for Li⁺ among the alkali cations, the first reconstitution of Li⁺-selective permeation in lipid bilayer membranes. This complexone acts as an equilibrium-domain carrier for Ag⁺> Li⁺>Tl⁺>Na⁺>NH ₄ ⁺ >Rb⁺>Cs⁺ over a wide range of experimental conditions. The major type of membrane-permeating species formed is a 21 carrier/cation complex dominant except at the lowest salt and carrier concentrations where a 11 carrier/cation, with a similar selectivity sequence, can be detected. Among the groupIa cations the selectivity sequence in bilayers, Li⁺>Na⁺>K⁺>Rb⁺>Cs⁺, is similar to that previously found for this molecule in thick solvent-polymer membrane electrodes. We find this carrier to be more selective to Ag⁺ than to any other monovalent cation yet studied. This high Ag⁺ selectivity is used, together with the dependence of the selectivity on the nature of the N-amide substitutents, to argue that the imide oxygens play a major role as ligands.     

K+ influx components in ascites cells: The effects of agents interacting with the (Na++K+)-pump

Summary Several agents known to interact with the (Na⁺+K⁺)-pump were tested for their effects on the components of steady-state K⁺ flux in ascites cells.⁸⁶Rb⁺ was used as a tracer for K⁺, and influx was differentiated into a ouabain-inhibitable pump component, a Cl^–-dependent and furosemide-sensitive exchange component, and a residual leak flux. All agents tested (ouabain, quercetin, oligomycin, phosphate) affected both the pump flux and the Cl^–-linked flux. These findings suggest a linkage between the activity of the Na/K ATPase and the Cl^–-dependent K⁺ exchange flux. In the discussion we point out that the mechanism of this linkage could be direct; e.g., Cl^–-dependent exchange may represent a mode of operation of the Na/K ATPase. However, data from this and other systems tend to suggest an indirect linkage between the Na⁺ pump and a KCl symporter, perhaps via a change in the level of intracellular ATP.     

The energy transmission in ATP synthase: From the γ-c rotor to the α3β3 oligomer fixed by OSCP-b stator via the βDELSEED sequence

ATP synthase (F₀F₁) is driven by an electrochemical potential of H⁺ (H⁺). F₀F₁ is composed of an ion-conducting portion (F₀) and a catalytic portion (F₁). The subunit composition of F₁ is ₃₃. The active ₃₃ oligomer, characterized by X-ray crystallography, has been obtained only from thermnophilic F₁ (TF₁). We proposed in 1984 that ATP is released from the catalytic site (C site) by a conformational change induced by the DELSEED sequence via -F₀. In fact, cross-linking of DELSEED to stopped the ATP-driven rotation of in the center of ₃₃. The torque of the rotation is estimated to be 420 pN·å from the H⁺ and H⁺-current through F₀F₁. The angular velocity () of is the rate-limiting step, because H⁺ increased theV _max of H⁺ current through F₀, but not theK _m (ATP). The rotational unit of F₀ (=ab₂c₁₀) is /5, while that in ₃₃ is 2/3. This difference is overcome by an analog-digital conversion via elasticity around DELSEED with a threshold to release ATP. The distance at the C site is about 9.6 å (2,8-diN₃-ATP), and tight Mg-ATP binding in ₃₃ was shown by ESR. The rotational relaxation of TF₁ is too rapid (=100 nsec), but the rate of AT(D)P-induced conformational change of ₃₃ measured with a synchrotron is close to . The ATP bound between the P-loop and E188 is released by the shift of DELSEED from RGL. Considering the viscosity resistance and inertia of the free rotor (-c), there may be a stator containing OSCP (= of TF₁) and F₀-d to hold free rotation of ₃₃.     

Cell pH and luminal acidification inNecturus proximal tubule

Summary Cellular potential and pH measurements (pH _i ) were carried out in the perfused kidney ofNecturus on proximal tubules with standard and recessed-tip glass microelectrodes under control conditions and after stimulation of tubular bicarbonate reabsorption. Luminal pH and net bicarbonate reabsorption were measured in parallel experiments with recessed-tip glass or antimony electrodes, both during stationary microperfusions as well as under conditions of isosmotic fluid transport. A mean cell pH of 7.15 was obtained in control conditions. When the luminal bicarbonate concentration was raised to 25 and 50mm, pH _i rose to 7.44 and 7.56, respectively. These changes in pH _i were fully reversible. Under all conditions intracellular H⁺ was below electrochemical equilibrium. Thus the maintenance of intracellular pH requires active H⁺ extrusion across one or both of the cell membranes. The observed rise in pH _i and the peritubular depolarization after stimulation of bicarbonate reabsorption are consistent with enhanced luminal hydrogen ion secretion and augmentation of peritubular bicarbonate exit via an anion-conductive transport pathway.     

A K+-selective,three-state channel from fragmented sarcoplasmic reticulum of frog leg muscle

Summary Sarcoplasmic reticulum (SR) vesicles from frog leg muscle were fused with a planar phospholipid bilayer by a method described previously for rabbit SR. As a result of the fusion, K⁺-selective conduction channels are inserted into the bilayer. Unlike the two-state rabbit channel, the frog channel displays three states: a nonconducting (closed) state and two conducting states and . In 0.1m K⁺ the single-channel conductances are 50 and 150 pS for and , respectively. The probabilities of appearearance of the three states are voltage-dependent, and transitions between the closed and states proceed through the state. Both open states follow a quantitatively identical selectivity sequence in channel conductance: K⁺>NH ₄ ⁺ >Rb⁺>Na⁺>Li⁺>Cs⁺. Both open states are blocked by Cs⁺ asymmetrically in a voltage-dependent manner. The zero-voltage dissociation constant for blocking is the same for both open states, but the voltage-dependences of the Cs⁺ block for the two states differ in a way suggesting that the Cs⁺ blocking site is located more deeply inside the membrane in the than in the state.     

Na+-translocating NADH-quinone reductase of marine and halophilic bacteria

The respiratory chain of marine and moderately halophilic bacteria requires Na⁺ for maximum activity, and the site of Na⁺-dependent activation is located in the NADH-quinone reductase segment. The Na⁺-dependent NADH-quinone reductase purified from marine bacteriumVibrio alginolyticus is composed of three subunits, , , and , with apparentM _r of 52, 46, and 32kDa, respectively. The FAD-containing -subunit reacts with NADH and reduces ubiquinone-1 (Q-1) by a one-electron transfer pathway to produce ubisemiquinones. In the presence of the FMN-containing -subunit and the -subunit, Q-1 is converted to ubiquinol-1 without the accumulation of free radicals. The reaction catalyzed by the -subunit is strictly dependent on Na⁺ and is strongly inhibited by 2-n-heptyl-4-hydroxyquinoline N-oxide (HQNO), which is tightly coupled to the electrogenic extrusion of Na⁺. A similar type of Na⁺-translocating NADH-quinone reductase is widely distributed among marine and moderately halophilic bacteria. The respiratory chain ofV. alginolyticus contains another NADH-quinone reductase which is Na⁺ independent and has no energy-transducing capacity. These two types of NADH-quinone reductase are quite different with respect to their mode of quinone reduction and their sensitivity toward NADH preincubation.     

13Cα and 13Cβ chemical shifts as a tool to delineate β-hairpin structures in peptides

Unravelling the factors that contribute to the formation and the stability of -sheet structure in peptides is a subject of great current interest. A -hairpin, the smallest -sheet motif, consists of two antiparallel hydrogen-bonded -strands linked by a loop region. We have performed a statistical analysis on protein -hairpins showing that the most abundant types of -hairpins, 2:2, 3:5 and 4:4, have characteristic patterns of ¹³C and ¹³C conformational shifts, as expected on the basis of their and angles. This fact strongly supports the potential value of ¹³C and ¹³C conformational shifts as a means to identify -hairpin motifs in peptides. Their usefulness was confirmed by analysing the patterns of ¹³C and ¹³C conformational shifts in 13 short peptides, 10–15 residues long, that adopt -hairpin structures in aqueous solution. Furthermore, we have investigated their potential as a method to quantify -hairpin populations in peptides.     

Structural and Functional Rearrangements of Mesophyll as a Probable Basis for the Cytokinin-Dependent Assimilate Translocation in Detached Leaves

The effects of benzyladenine (BA) on the mesophyll functioning, such as osmotic potential (), the effect of the inhibitors of ⁺-ATPase on the influx of ¹⁴C-sucrose, the direction of carbon metabolism, and the rate of dark respiration, were followed in the detached leaves of pumpkin (Cucurbita pepo L.) and broad beans (Vicia faba L.). BA elevated and established a gradient of (_p) between the treated and untreated leaf regions. The inhibitors of H⁺-ATPase did not affect the BA-induced influx of ¹⁴C-sucrose. The changes were accompanied with the elevated synthesis of starch and other polymeric compounds and the diminished synthesis of the substances of relatively low molecular weight. The stimulation of dark respiration was short and inconsiderable. The author concludes that the BA-induced transport was a passive process related to a increase. Leaf expansion accompanied by the synthesis of high-molecular-weight substances essential for cell growth and by starch synthesis apparently increased the sink capacity of the BA-treated detached leaves. The diminished efflux from the leaf blade was probably related to a lowered level of the transportable carbon compounds restricting their entry into the phloem. The influx induction could result from the activation of growth and metabolic processes, the decline in the number of organic molecules per cell volume unit, and the development of _p between the source and sink leaf regions.     

Proton translocation in corn coleoptiles: ATPase or redox chain?

The O₂ dependence of net H⁺ efflux of maize coleoptiles has been investigated. Below 100 M O₂, H⁺ efflux in young (1 cm long) coleoptiles is markedly decreased while old (7 cm long) coleoptiles show a decline only at 10 M O₂. Old coleoptiles show the same decrease in net H⁺ efflux as young ones if treated with fusicoccin. The ratio of alteration of CO₂ production to the change in net proton efflux is about 1:1 at 40–80 M O₂ but not at 10 M O₂. An influx can be observed at 10 M O₂ in young as well as in old coleoptiles if the H⁺ concentration is held at values below pH 6.5. Lower O₂ concentrations lead to an increase of net H⁺ efflux, which might be caused by leaching of organic acids resulting from anaerobic processes, but CO₂ production is not significantly changed at these values. It is proposed that more than one system is responsible for proton translocation across the plasmalemma. One of the systems has a high sensitivity to reduced O₂ concentration which is within the same range as the high K_m of the alternative path.Abbreviation FC fusicoccin     

A kinetic study of the anaerobic digestion of piggery waste using down-flow stationary fixed film reactors

Summary In this paper the behaviour of the down-flow stationary fixed film digesters is studied at laboratory and bench scale. Several organic loading rates are applied to the reactors in order to examine the support surface behaviour. Specific support surfaces of about 50 m²/m³ void volume seems to be optimal. A set of experiments carried out in a continuous stirred reactor is used to fit the kinetic constants of the Chen and Hashimoto's model. The model is then used to assess its applicability to the DSFF digesters. The results show that its application, is possible as a first approximation.Nomenclature B₀ Ultimate methane yield (m³ CH₄/Kg VS) - B Specific methane production (m³ CH₄/Kg VS) - CSTR Continuous stirred tank reactor - DSFF Down-flow Stationary Fixed Film - HRT Hydraulic retention time (days) - K Kinetic constant of the Chen and Hashimoto model (dimensionless) - S Biodegradable substrate concentration (g/l) - SLR Superficial loading rate (Kg VS/m²·d) - SSS Specific support surface (m² support surface/m³ digester void volume) - S₀ Initial substrate concentration (g/l) - VS Volatile solids (g/l) - VFA Volatile Fatty Acids (mg/dm³) - Microorganisms specific growth (day^-1) - _m Kinetic constant of Chen and Hashimoto's model (day^-1) - Retention time (days) - _m Minimum retention time to avoid microorganisms washout (days)     

Monovalent Cations Contribute to T-type Calcium Channel (Ca<Subscript>V</Subscript>3.1 and Ca<Subscript>V</Subscript>3.2) Selectivity

Low voltage-activated (LVA) Ca²⁺ channels regulate chemical signaling by their ability to select for Ca²⁺. Whereas Ca²⁺ is the main permeating species through Ca²⁺ channels, Ca²⁺ permeation may be modified by abundant intra- and extracellular monovalent cations. Therefore, we explored monovalent cation regulation of LVA Ca²⁺ permeation in the cloned T-type Ca²⁺ channels 1G (Ca_V3.1) and 1H (Ca_V3.2). In physiological [Ca²⁺], the reversal potential in symmetrical Li⁺ was 19 mV in 1G and 18 mV in 1H, in symmetrical Cs⁺ the reversal potential was 36 mV in 1G and 37 mV in 1H, and in the bi-ionic condition with Li⁺ in the bath and Cs⁺ in the pipette, the reversal potential was 46 mV in both 1G and 1H. When Cs⁺ was used in the pipette, replacement of external Cs⁺ with Li⁺ (or Na⁺) shifted the reversal potential positive by 5–6 mV and increased the net inward current in 1G. Taken together the data indicate that in physiological [Ca²⁺], external Li⁺ (or Na⁺) permeates more readily than external Cs⁺, resulting in a positive shift of the reversal potential. We conclude that external monovalent cations dictate T-type Ca²⁺ channel selectivity by permeating through the channel. Similar to Li⁺, we previously reported that external [H⁺] can regulate T-type Ca²⁺ channel selectivity. 1Hs selectivity was more sensitive to external pH changes compared to 1G. When Cs⁺ was used in the pipette and Li⁺ was used in the bath external acidification from pH_o 7.4 to 6.0 caused a negative shift of the reversal by 8 mV in 1H. Replacement of internal Cs⁺ with Li⁺ reduced the pH-induced shift of the reversal potential to 2 mV. We conclude that, similar to other external monovalent cations, H⁺ can modify T-type Ca²⁺ channel selectivity. However, in contrast to external monovalent ions that readily permeate, H⁺ regulate T-type Ca²⁺ channel selectivity by increasing the relative permeability of the internal monovalent cation. Present address: B.P. Delisle, Department of Medicine, The University of Wisconsin, Madison, WI 53706, USA     

Function and regulation of the avian caecal bulb: influence of dietary NaCl and aldosterone on water and electrolyte fluxes in the hen (Gallus domesticus) perfused in vivo

Summary The function of the caecal bulb, and its adaptation to chronic high- or low-Na⁺ intake, was investigated by in vivo perfusion of anaesthetised birds. Effects of acute aldosterone injection (125 g·kg^–1 body mass) were also measured.Evidence was found for primary active net absorption of Na⁺, inducing parallel Na-linked absorption of water and Cl^– and secretion of K⁺. Around 20–35% of total Cl^– absorption and K⁺ secretion were independent of Na⁺ fluxes, and these components appear to be driven by passive processes with apparent conductances of 6.3×10^–3 (G _Cl) and 1.1×10^–3 (G _K) S·cm^–2.Acetate (40mM) stimulated Na⁺ fluxes (8.5–9.9 Eq·cm^–2·h^–1) and Na-linked water fluxes (27–44 l·cm^–2·h^–1). Increased coupling ratios (2.9–4.6 l·Eq^–1) and other data indicate that these effects may be due to increased osmotic permeabilities of barriers involved in the Na-linked water transfer pathway.Low-Na⁺ maintenance enhanced EPD (49–69 mV, serosa positive) and all net fluxes:J _Na (6.8–11.6);J _K (–3.2––4.3);J _Cl (4.3–5.6 Eq·cm serosal area^–2·h^–1);J _v (28–43 l·cm^–2·h^–1) (mucosal-serosal fluxes positive).Acute aldosterone enhancedJ _Na (10.8–14.0 Eq·cm^–2·h^–1) and EPD (54–66 mV) by 3 h after injection, but had no effect on the Na-linked components ofJ _K orJ _Cl.Abbreviations ECPD, EPD Electrochemical or electrical potential difference - G _Cl ,G _K ionic conductances (Cl^–, K⁺) - J _v ,J _ion net volume or ion flux rate, mucosa-serosa positive;P _d (Cl) diffusive permeability coefficient (of Cl^–) - SEDM standard error of difference between means     

Pump-leak sodium fluxes in low salt corn roots

Summary The influx and efflux of sodium from 4-hr washed, low salt corn roots (Zea mays L.) has been studied for characterization of passive and active components. Initial Na⁺ content of the roots is very low, 2.25±0.4 mol/g fresh weight. Na⁺ influx in the presence of 0.2mm Ca²⁺ and 0.002 to 20mm K⁺ is passive (a leak) based upon Goldman-type models, being determined by Na⁺ and cell potential (). Na⁺ was not transported by the K⁺ carrier and influx was unaffected by 50 m dicyclohexylcarbodiimide (DCCD). Permeability of the cells to Na⁺ was of the same order asP _k.Efflux of Na⁺ was by an efficient and rapid active transport system (a pump), thus accounting for the failure of these roots to accumulate high levels of Na⁺. In short-term loading and efflux experiments, internal Na⁺ turnover had a half-time of about 5 min. Sodium efflux was unaffected by DCCD. Net H⁺ flux was zero in the presence of DCCD regardless of sodium efflux, indicating absence of Na⁺/H⁺ antiport. Efflux of Na⁺ was equally rapid into medium containing no Na⁺ and only 0.002mm K⁺. K⁺ influx accounted for less than 4% of Na⁺ efflux, prompting the hypothesis that the Na⁺ (or cation?) efflux pump is the second electrogenic system previously defined based upon electrophysiological measurements.     

Tissue culture ofKarwinskia humboldtiana—a plant producing toxins with antitumoural effects

Isolated embryos ofKarwinskia humboldtiana were cultured in vitro. The growth of embryos and development to plantlets on woody plant medium supplemented with indole-3-acetic acid 6.10^-2 mol l^–1, gibberellic acid (GA₃) 3.10^-2 mol l^–1, and 6-benzylaminopurine (BA) 2 mol l^–1 was obtained. Multiplication of shoots and rooting of excised shoots has been achieved. Callus formation on modified Murashige-Skoog medium supplemented with 1-naphthaleneacetic acid 10 mol l^–1, GA₃ 14 mol l^–1, and kinetin 5 mol l^–1 on hypocotyls, or on root cultures on medium supplemented with 2.4-dichlorophenoxyacetic acid 10 mol l^–1 and BA 10 mol l^–1 was induced.Abbreviations BA 6-benzylaminopurine - 2,4-d 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - IAA indole-3-acetic acid - NAA 1-naphthaleneacetic acid - TEM transmission electron microscopy     

Influence of an extracellular volume expansion (ECVE) on renal amino acid- and sodium handling in patients with autosomal dominant polycystic kidney disease (ADPKD)

Summary Although ADPKD is one of the first kidney diseases to be understood from the gene to the pathogenesis of clinical abnormalities, there were no data concerning the renal handling of amino acids and possible disorders of amino acid (AA) pattern in these patients. Therefore, in 9 patients suffering from ADPKD and in 8 healthy normal persons (NP) renal amino acid excretion was measured before and after extracellular volume expansion (ECVE) (21 of physiological electrolyte solution). Renal function was stable in both groups (serum creatinine: ADPKD: 85.1 ± 18.4 vs. NP 84.4 ± 13.5 mol/l; GFR: 93.8 ± 16.4 vs. 104.4 ± 9.4 ml/min/1.73 m²). Mean blood pressure was higher in ADPKD patients than in NP (99.4 ± 2.6 vs. 85.5 ± 2.4 mmHg), but did not change after ECVE. After ECVE in both groups, urine volume increased distinctly, whereas GFR was only slightly enhanced. The plasma concentrations of leucine, glycine, valine, threonine, glutamine, and alanine were significantly higher in controls than in ADPKD patients. The amino acid reabsorption capacity was reduced in ADPKD patients in 12 of 21 amino acids before ECVE. After ECVE, the fractional excretion of amino acids (FE_AA) increased only in NP. In parallel with changes in amino acid handling, the FE_Na (%) after ECVE increased both in ADPKD patients and in NP (before ECVE - ADPKD: 1.22 ± 0.23 vs. NP: 1.53 ± 0.23; after ECVE: 3.17 ± 0.25 (ADPKD) vs. 2.74 ± 0.22/NP; (ADPKD p 0.01, NP p 0.02) whereas FE_Li (%) increased significantly only in ADPKD (p 0.045) range (before ECVE - ADPKD: 25.8 ± 8.9 vs. NP: 20.5 ± 4.0; after ECVE: 41.4 ±15.4 vs. 25.2 ± 3.9). Furthermore, concentrations of cGMP (pmol/ml) in plasma increased after ECVE (before ECVE - ADPKD: 5.31 ± 0.56 vs. NP: 6.65 ±0.79; after ECVE: 11.31 ± 1.66 vs. 11.30 ± 1.91; p 0.05). Na⁺-dependent and, perhaps, NO-mediated processes in the reabsorption of AA in the proximal tubule seem to be different in ADPKD and may be related to different distributions of receptors and ATP-dependent transport systems with pathogenetic impact on abnormal transtubular fluid transport in ADPKD.     

Evidence for a K+ channel in bovine chromaffin granule membranes: single-channel properties and possible bioenergetic significance

A K⁺ channel was incorporated into voltage-clamped planar lipid bilayers from bovine chromaffin granules and resealed granule membranes (ghosts). It was not incorporated from plasma membrane-rich fractions from the adrenal medulla. The channel had a conductance of 400 pS in symmetric 450 mM KCI, with the permeability sequence K⁺ > Rb⁺ > Cs⁺ > Na⁺ > Li⁺, and was insensitive to both Ca²⁺ and charybdotoxin. It exhibited complex gating kinetics, consistent with the presence of multiple open and closed states, and its gating was voltage-dependent. The channels appeared to incorporate into bilayers with the same orientation, and were blocked from one side (the side of vesicle addition) by 0.2-1 mM TEA'. The block was slightly voltage-dependent. Acidification of resealed granule membranes in response to external ATP (which activated the vacuolartype ATPase) was significantly reduced in the presence of 1 mM intralumenal TEACI (with 9 mM KCl), and parallel measurements with the potential-sensitive dye Oxonol V showed that such vesicles tended to develop higher internal-positive membrane potentials than control vesicles containing only 10 mM KCI. 1 mM TEA⁺ had no effect on proton-pumping activity when applied externally, and did not directly affect either the proton-pumping or ATP hydrolytic activity of the partially-purified ATPase. These results suggest that chromaffin granule membranes contain a TEA⁺-sensitive K⁺ channel which may have a role in regulating the vesicle membrane potential. Correspondence to: R. H. Ashley     

CCCP activation of the reconstituted NaK-pump

Summary In the NaK-ATPase proteoliposomes (PLs), the NaK-pump activity, Na⁺ uptake, and ATP hydrolysis were apparently enhanced by carbonyl cyanidem-chlorophenylhydrazone (CCCP) and other ionophores without ion gradients. These ionophore effects were not cation specific. Without ionophores, the PL's ATPase activity fell to its steady-state value within 3 sec at 15°C. This decrease in activity disappeared in the presence of CCCP. Since CCCP is believed to enhance proton mobility across the lipid bilayer and dissipate membrane potential (V _m ), we postulated that aV _m build-up partially inhibits the PLs by changing the conformation of the NaK-pump, and that CCCP eliminated this partial inhibition. Since this activation required extracellular K⁺ and high ATP concentration in the PLs, CCCP must affect the conversion between the phosphorylated forms of NaK-ATPase (EP); this step has been suggested by Goldschlegger et al. (1987) to be the voltage-sensitive step (J. Physiol. (London) 387:331–355). Although cytoplasmic K⁺ accelerated the change of ADP-and K⁺-sensitive EP (E^*P) to K⁺-sensitive ADP-insensitive EP (E₂P), CCCP did not compete with cytoplasmic K⁺ when cytoplasmic Na⁺ was saturated. When the PLs were phosphorylated with 20 m ATP and 20 m palmitoyl CoA instead of with high concentration of ATP, CCCP increased the E^*P content and decreased the ADP-sensitive K⁺-insensitive EP (E₁P). The results described above suggest that CCCP affects the E₁P to E^*P change in the E₁PE^*PE₂P conversion and that this reaction step is inhibited byV _m .     

Lectin like properties and differential sugar binding characteristics of C-reactive proteins purified from sera of normal and pollutant induced Labeo rohita

Different forms of C-reactive proteins (CRPs) have been purified to electrophoretic homogeneity from the sera of Labeo rohita confined in freshwater (CRP_N) and water polluted with nonlethal doses of cadmium (CRP_Cd) or mercury (CRP_Hg). CRP_N[emsp4 ], CRP_Cd[emsp4 ], and CRP_Hg show remarkable differences in their electrophoretic mobility but exhibit strong immunological cross reactivity. All these CRPs exhibit variable agglutination properties with erythrocytes from diverse sources in presence of Ca⁺², which could be inhibited by a variety of sugars showing specificity for galactose. Inhibition results show that the potency of galactose as an inhibitor increases about 4 fold in the process of transformation of CRP_N to CRP_Cd and CRP_Hg[emsp4 ]. In case of CRP_N[emsp4 ], Gal (11) Gal and oNO₂ phenyl -Gal show highest inhibitory potency while oNO₂-phenyl -Gal is the most potent inhibitor for CRP_Cd and CRP_Hg but the potency of Gal (11) Gal reduced drastically. 6-phosphate D-Gal and stachyose are 20 times weaker inhibitors than D-Gal for induced CRP mediated agglutination, in contrast, these sugars are only 6 times weaker for CRP_N[emsp4 ]. Dissociation constants of the binding of CRP_N with phosphoryl choline (PC) and galactose are about 9[emsp4 ]mM and PC binding causes a change in the and conformations of these CRPs.