Fed-batch cultivation of Arthrospira (Spirulina) platensis: Potassium nitrate and ammonium chloride as simultaneous nitrogen sources

Arthrospira platensis was cultivated in minitanks at 13 klux, using a mixture of KNO(3) and NH(4)Cl as nitrogen source. Fed-batch daily supply of NH(4)Cl at exponentially-increasing feeding rate allowed preventing ammonia toxicity and nitrogen deficiency, providing high maximum cell concentration (X(m)) and high-quality biomass (21.85 mg chlorophyll g cells(-1); 20.5% lipids; 49.8% proteins). A central composite design combined to response surface methodology was utilized to determine the relationships between responses (X(m), cell productivity and nitrogen-to-cell conversion factor) and independent variables (KNO(3) and NH(4)Cl concentrations). Under optimum conditions (15.5 mM KNO3; 14.1 mM NH(4)Cl), X(m) was 4327 mg L(-1), a value almost coincident with that obtained with only 25.4 mM KNO(3), but more than twice that obtained with 21.5 mM NH(4)Cl. A 30%-reduction of culture medium cost can be estimated when compared to KNO(3)-batch runs, thus behaving as a cheap alternative for the commercial production of this cyanobacterium. (C) 2010 Elsevier Ltd. All rights reserved.

Manufacture of low-sodium Minas fresh cheese: Effect of the partial replacement of sodium chloride with potassium chloride

We investigated the effect of sodium reduction by partial substitution of sodium chloride (NaCl) with potassium chloride (KCl) on the manufacture of Minas fresh cheese during 21 d of refrigerated storage. Four treatments of low-sodium Minas fresh cheese were manufactured, with partial replacement of NaCl by KCl at 0, 25, 50, and 75% (wt/wt), respectively. The cheeses showed differences in the content of moisture, ash, protein, salt, and lipid contents, as well as on the extent of proteolysis and hardness throughout the storage period. However, no difference was observed among treatments within each storage day tested. The partial substitution of NaCl by KCl decreased up to 51.8% the sodium concentration of the cheeses produced. The consumer test indicated that it is possible to manufacture a low-sodium Minas fresh cheese that is acceptable to consumers by partial substitution of NaCl by KCl at 25% (wt/wt) in the salting step.

Synthesis of potassium and tetra n-butylammonium 2-substituted-1,3-dithianotrifluoroborate salts and addition to chiral cyclic N-acyliminium ions

The synthesis of potassium 2-substituted-1,3-dithianotrifluoroborate salts and tetra-n-butyl ammonium derivatives is described. The reaction proceeds under mild reaction conditions and the corresponding products were obtained in moderate to good yields. The reactivity of these compounds in rections with chiral cyclic N-acyliminium ions was evaluated.

Synthesis of 2-Aryl- and 2,5-Diarylfurans and Thiophenes by Suzuki-Miyaura Reactions Using Potassium Trifluoroborate Salts and Heteroaryltellurides

The Suzuki-Miyaura cross-coupling reaction of 2-(butyltellanyl) or 2,5-bis-(butyltellanyl)furans and thiophenes with potassium aryltrifluoroborate salts catalyzed by palladium afforded 2-aryl- or 2,5-diaryl-furans and thiophenes in moderate to good yields.

Acidosis induces relaxation mediated by nitric oxide and potassium channels in rat thoracic aorta

We investigated the mechanism by which extracellular acidification promotes relaxation in rat thoracic aorta. The relaxation response to HCl-induced extracellular acidification (7.4 to 6.5) was measured in aortic rings pre-contracted with phenylephrine (Phe, 10(-6) M) or KCl (45 mM). The vascular reactivity experiments were performed in endothelium-intact and denuded rings, in the presence or absence of indomethacin (10(-5) M), L-NAME (10(-4) M), apamin (10(-6) M), and glibenclamide (10(-5) M). The effect of extracellular acidosis (pH 7.0 and 6.5) on nitric oxide (NO) production was evaluated in isolated endothelial cells loaded with diaminofluorescein-FM diacetate (DAF-FM DA, 5 mu M). The extracellular acidosis failed to induce any changes in the vascular tone of aortic rings pre-contracted with KCl, however, it caused endothelium-dependent and independent relaxation in rings pre-contracted with Phe. This acidosis induced-relaxation was inhibited by L-NAME, apamin, and glibenclamide, but not by indomethacin. The acidosis (pH 7.0 and 6.5) also promoted a time-dependent increase in the NO production by the isolated endothelial cells. These results suggest that extracellular acidosis promotes vasodilation mediated by NO, K(ATP) and SK(Ca), and maybe other K(+) channels in isolated rat thoracic aorta. (C) 2011 Elsevier B.V. All rights reserved.

Solution structure and proposed binding mechanism of a novel potassium channel toxin kappa-conotoxin PVIIA

Background: kappa-PVIIA is a 27-residue polypeptide isolated from the venom of Conus purpurascens and is the first member of a new class of conotoxins that block potassium channels. By comparison to other ion channels of eukaryotic cell membranes, voltage-sensitive potassium channels are relatively simple and methodology has been developed for mapping their interactions with small-peptide toxins, PVIIA, therefore, is a valuable new probe of potassium channel structure. This study of the solution structure and mode of channel binding of PVIIA forms the basis for mapping the interacting residues at the conotoxin-ion channel interface. Results: The three-dimensional structure of PVIIA resembles the triple-stranded beta sheet/cystine-knot motif formed by a number of toxic and inhibitory peptides. Subtle structural differences, predominantly in loops 2 and 4, are observed between PVIIA and other conotoxins with similar structural frameworks, however. Electrophysiological binding data suggest that PVIIA blocks channel currents by binding in a voltage-sensitive manner to the external vestibule and occluding the pore, Comparison of the electrostatic surface of PVIIA with that of the well-characterised potassium channel blocker charybdotoxin suggests a likely binding orientation for PVIIA, Conclusions: Although the structure of PVIIA is considerably different to that of the alpha K scorpion toxins, it has a similar mechanism of channel blockade. On the basis of a comparison of the structures of PVIIA and charybdotoxin, we suggest that Lys19 of PVIIA is the residue which is responsible for physically occluding the pore of the potassium channel.

Photolytic manipulation of [Ca2+](i) reveals slow kinetics of potassium channels underlying the afterhyperpolarization in hipppocampal pyramidal neurons

The identity of the potassium channel underlying the slow, apamin-insensitive component of the afterhyperpolarization current (sl(AHP)) remains unknown. We studied sl(AHP) in CA1 pyramidal neurons using simultaneous whole-cell recording, calcium fluorescence imaging, and flash photolysis of caged compounds. Intracellular calcium concentration ([Ca2+](i)) peaked earlier and decayed more rapidly than sl(AHP). Loading cells with low concentrations of the calcium chelator EGTA slowed the activation and decay of sl(AHP). In the presence of EGTA, intracellular calcium decayed with two time constants. When [Ca2+](i) was increased rapidly after photolysis of DM-Nitrophen, both apamin-sensitive and apamin-insensitive outward currents were activated. The apamin-sensitive current activated rapidly (<20 msec), whereas the apamin-insensitive current activated more slowly (180 msec). The apamin-insensitive current was reduced by application of serotonin and carbachol, confirming that it was caused by sl(AHP) channels. When [Ca2+](i) was decreased rapidly via photolysis of diazo-2, the decay of sl(AHP) was similar to control (1.7 sec). All results could be reproduced by a model potassium channel gated by calcium, suggesting that the channels underlying sl(AHP) have intrinsically slow kinetics because of their high affinity for calcium.

Spider toxins: A new group of potassium channel modulators

Spider toxins that target potassium channels constitute a new class of pharmacological tools that can be used to probe the structure and function of these channels at the molecular level. The limited studies performed to date indicate that these peptide toxins may facilitate the analysis of K+ channels that have proved insensitive to peptide inhibitors isolated from other animal sources. Thus far, two classes of K+ channel-selective spider toxins have been isolated, sequenced, and pharmacologically characterised - the hanatoxins (HaTx) from Grammastola spatulata and heteropodatoxins (HpTx) from Heteropoda venatoria. The hanatoxins block Kv2.1 and Kv4.2 voltage-gated K+ channels. In Kv2.1 K+ channels this occurs as a consequence of a depolarising shift in the voltage dependence of activation and not by occlusion of the channel pore. These toxins show minimal sequence homology with other peptide inhibitors of K+ channels, but they do share some homology with other ion channel toxins from spiders, particularly with regard to the spacing between cysteine residues. We have recently isolated three K+ channel antagonists from the venom of the Australian funnel-web spider Hadronyche versuta; at least two of these toxins are likely to constitute a new class of spider toxins active on K+ channels as they are approximately twice as large as HaTx and HpTx.

Catalytic conversion to N2O to N2 over potassium catalyst supported on activated carbon

Catalytic conversion of N2O to N-2 With potassium catalysts supported on activated carbon (K/AC) was investigated. Potassium proves to be much more active and stable than either copper or cobalt because potassium possesses strong abilities both for N2O chemisorption and oxygen transfer. Potassium redispersion is found to play a critical role in influencing the catalyst stability. A detailed study of the reaction mechanism was conducted based upon three different catalyst loadings. It was found that during temperature-programmed reaction (TPR), the negative oxygen balance at low temperatures (< 50 degrees C) is due to the oxidation of the external surface of potassium oxide particles, while the bulk oxidation accounts for the oxygen accumulation at higher temperatures (below ca. 270 degrees C). N2O is beneficial for the removal of carbon-oxygen complexes because of the formation of CO2 instead of CO and because of its role in making the chemisorption of produced CO2 on potassium oxide particles less stable. A conceptual three-zone model was proposed to clarify the reaction mechanism over K/AC catalysts. CO2 chemisorption at 250 degrees C proves to be an effective measurement of potassium dispersion. (C) 1999 Academic Press.

Assessment of intracellular water by whole body bioelectrical impedance and total body potassium in HIV-positive patients

.:Abstract-Objective: Bioelectrical impedance analysis (BIA) is widely used as bedside assessment of body composition. Body cell mass (BCM) and intracellular water (ICW) are clinically important body compartments. Estimates of ICW obtained from BIA by different calculation approaches were compared to a reference method in male HIV-infected patients. Patients: Representative subsample of clinically stable HIV-infected outpatients, consisting of 42 men with a body mass index of 22.4 +/- 3.8 kg/m(2) (range, 13-31 kg/m(2)). Methods: Total body potassium was assessed in a whole body counter, and compared to 50 kHz mono-frequency BIA and multifrequency bioelectrical impedance spectroscopy. Six different prediction equations for ICW from BIA data were applied. Methods were compared by the Bland-Altman method. Results: BIA-derived ICW estimates explained 58% to 73% of the observed variance in ICW (TBK), but limits of confidence were wide (-16.6 to +18.2% for the best method). BIA overestimated low ICW (TBK) and underestimated high ICW (TBK) when normalized for weight or height. Mono- and multifrequency BIA were not different in precision but population-specific equations tended to narrower confidence limits. Conclusion: BIA is an unreliable method to estimate ICW in this population, in contrast to the better established estimation of total body water and extracellular water. Potassium depletion in severe malnutrition may contribute to this finding but a major part of the residual between methods remains unexplained. (C) 2000 Harcourt Publishers Ltd.

Calcium-activated potassium currents in mammalian neurons

1. Influx of calcium via voltage-dependent calcium channels during the action potential lends to increases in cytosolic calcium that can initiate a number of physiological processes. One of these is the activation of potassium currents on the plasmalemma. These calcium-activated potassium currents contribute to action potential repolarization and are largely responsible for the phenomenon of spike frequency adaptation. This refers to the progressive slowing of the frequency of discharge of action potentials during sustained injection of depolarizing current. In some cell types, this adaptation is so marked that despite the presence of depolarizing current, only a single spike (or a few spikes) is initiated, Following cessation of current injection, slow deactivation of calcium-activated potassium currents is also responsible for the prolonged hyperpolarization that often follows, 2. A number of macroscopic calcium-activated potassium currents that can be separated on the basis of kinetic and pharmacological criteria have been described in mammalian neurons. At the single channel level, several types of calcium-activated potassium channels also have been characterized. While for some macroscopic currents the underlying:single channels have been unambiguously defined, for other currents the identity of the underlying channels is not clear. 3. In the present review we describe the properties of the known types of calcium-activated potassium currents in mammalian neurons and indicate the relationship between macroscopic currents and particular single channels.

Physiological role of calcium-activated potassium currents in the rat lateral amygdala

Principal neurons in the lateral nucleus of the amygdala (LA) exhibit a continuum of firing properties in response to prolonged current injections ranging from those that accommodate fully to those that fire repetitively. In most cells, trains of action potentials are followed by a slow after hyperpolarization (AHP) lasting several seconds. Reducing calcium influx either by lowering concentrations of extracellular calcium or by applying nickel abolished the AHP, confirming it is mediated by calcium influx. Blockade of large conductance calcium-activated potassium channel (BK) channels with paxilline, iberiotoxin, or TEA revealed that BK channels are involved in action potential repolarization but only make a small contribution to the fast AHP that follows action potentials. The fast AHP was, however, markedly reduced by low concentrations of 4-aminopyridine and alpha-dendrotoxin, indicating the involvement of voltage-gated potassium channels in the fast AHP. The medium AHP was blocked by apamin and UCL1848, indicating it was mediated by small conductance calcium-activated potassium channel (SK) channels. Blockade of these channels had no effect on instantaneous firing. However, enhancement of the SK-mediated current by 1-ethyl-2-benzimidazolinone or paxilline increased the early interspike interval, showing that under physiological conditions activation of SK channels is insufficient to control firing frequency. The slow AHP, mediated by non-SK BK channels, was apamin-insensitive but was modulated by carbachol and noradrenaline. Tetanic stimulation of cholinergic afferents to the LA depressed the slow AHP and led to an increase in firing. These results show that BK, SK, and non-BK SK-mediated calcium-activated potassium currents are present in principal LA neurons and play distinct physiological roles.

Channels underlying neuronal calcium-activated potassium currents

In many cell types rises in cytosolic calcium, either due to influx from the extracellular space, or by release from an intracellular store activates calcium dependent potassium currents on the plasmalemma. In neurons, these currents are largely activated following calcium influx via voltage gated calcium channels active during the action potentials. Three types of these currents are known: I-c. I-AHP and I-sAHP. These currents can be distinguished by clear differences in their pharmacology and kinetics. Activation of these potassium currents modulates action potential time course and the repetitive firing properties of neurons. Single channel studies have identified two types of calcium-activated potassium channel which can also be separated on biophysical and pharmacological grounds and have been named BK and SK channels. It is now clear that BK channels underlie Ic whereas SK channels underlie I-AHP. The identity of the channels underlying I-sAHP are not known. In this review, we discuss the properties of the different types of calcium-activated potassium channels and the relationship between these channels and the macroscopic currents present in neurons. (C) 2002 Elsevier Science Ltd. All rights reserved.

Calcium-activated potassium channels: Multiple contributions to neuronal function

Calcium-activated potassium channels are a large family of potassium channels that are found throughout the central nervous system and in many other cell types. These channels are activated by rises in cytosolic calcium largely in response to calcium influx via voltage-gated calcium channels that open during action potentials. Activation of these potassium channels is involved in the control of a number of physiological processes from the firing properties of neurons to the control of transmitter release. These channels form the target for modulation for a range of neurotransmitters and have been implicated in the pathogenesis of neurological and psychiatric disorders. Here the authors summarize the varieties of calcium-activated potassium channels present in central neurons and their defining molecular and biophysical properties.

The crustacean gill (Na(+),K(+))-ATPase: Allosteric modulation of high- and low-affinity ATP-binding sites by sodium and potassium

The blue crab, Callinectes danae, tolerates exposure to a wide salinity range employing mechanisms of compensatory ion uptake when in dilute media. Although the gill (Na(+), K(+))-ATPase is vital to hyperosmoregulatory ability, the interactions occurring at the sites of ATP binding on the molecule itself are unknown. Here, we investigate the modulation by Na(+) and K(+) of homotropic interactions between the ATP-binding sites, and of phosphoenzyme formation of the (Na(+),K(+))-ATPase from the posterior gills of this euryhaline crab. The contribution of the high- and low-affinity ATP-binding sites to maximum velocity was similar for both Na(+) and K(+). However, in contrast to Na(+), a threshold K(+) concentration triggers the appearance of the high-affinity binding sites, displacing the saturation curve to lower ATP concentrations. Further, a low-affinity site for phosphorylation is present on the enzyme. These findings reveal notable differences in the catalytic mechanism of the crustacean (Na(+),K(+))-ATPase compared to the vertebrate enzyme. (C) 2008 Elsevier Inc. All rights reserved.