Potassium inactivation

Potassium inactivation and impedance changes during spike electrogenesis in eel electroplaques. J. Gen. Physiol. 55 ... 

Fig. 1. An amplified outline scheme of the making of various wiaes, alternative products, by-products, and associated wastes (23). Ovals = raw materials, sources rectangles = wines hexagon = alternative products (decreasing wine yield) diamond = wastes. To avoid some complexities, eg, all the wine vinegar and all carbonic maceration are indicated as red. This is usual, but not necessarily tme. Similarly, malolactic fermentation is desired in some white wines. FW = finished wine and always involves clarification and stabilization, as in 8, 11, 12, 13, 14, 15, 33, 34, followed by 39, 41, 42. It may or may not include maturation (38) or botde age (40), as indicated for usual styles. Stillage and lees may be treated to recover potassium bitartrate as a by-product. Pomace may also yield red pigment, seed oil, seed tannin, and wine spidts as by-products. Sweet wines are the result of either arresting fermentation at an incomplete stage (by fortification, refrigeration, or other means of yeast inactivation) or addition of juice or concentrate.

Preparation of Balanoglossus luciferin. The residue of the first pH 6 extraction above was re-extracted with 50 mM potassium phosphate buffer, pH 8. After centrifugation, the supernatant was used as the standard luciferin preparation. Luciferin was highly labile and easily inactivated at an extreme pH, by heat, and also by freezing and thawing. The instability resembled that of certain proteins. 

Til tee successive tubule portions contribute to the ASDN the late portion of the distal convoluted tubule, the connecting tubule, and the collecting duct. The recent observation that collecting duct-specific inactivation of aENaC in the mouse kidney does not impair sodium and potassium balance, suggests that the more proximal nephron segments (late distal convoluted tubule, connecting tubule) are mainly important for-achieving sodium and potassium balance. 

Kv 3 -subunits are auxiliary subunits of Shaker-related Kv-channels, which belong to the Kvl subfamily of voltage-gated potassium channels. Kv(3 -subunits may function as chaperones in Kva -subunit assembly and may modulate the gating properties of Kv-channels. In particular, some Kv(3 -subunits may confer a rapid inactivation to otherwise non-inactivating Kv-channels. 

Regarding the use of other metals for this transformation, Shirai and co-workers reported that a system constituted by palladium(II) complex [Pd(p-Cl)(r -aUyl)]2 and thioether-imidazolium chloride 19 achieved the arylation of aldehydes with boronic acids [33] and potassium trifluoroborates in good to excellent yields (Scheme 7.5) [34], More recently, Buffard and Itami showed that a NKcod) / IPr-HCl system could catalyse the reaction of arylboronate esters and inactivated aldehydes and ketones (Scheme 7.5) [35]. 

Xanthine oxidase, a widely used source of superoxide, has been frequently applied for the study of the effects of superoxide on DNA oxidation. Rozenberg-Arska et al. [30] have shown that xanthine oxidase plus excess iron induced chromosomal and plasmid DNA injury, which was supposedly mediated by hydroxyl radicals. Ito et al. [31] compared the inactivation of Bacillus subtilis transforming DNA by potassium superoxide and the xanthine xanthine oxidase system. It was found that xanthine oxidase but not K02 was a source of free radical mediated DNA inactivation apparently due to the conversion of superoxide to hydroxyl radicals in the presence of iron ions. Deno and Fridovich [32] also supposed that the single strand scission formation after exposure of DNA plasmid to xanthine oxidase was mediated by hydroxyl radical formation. Oxygen radicals produced by xanthine oxidase induced DNA strand breakage in promotable and nonpromotable JB6 mouse epidermal cells [33]. 

Characteristic properties of endopectate lyases are the high pH optimum, and a requirement for Ca2+ ions in order to maintain catalytic activity. The pH optimum of various endopectate lyases ranges from 8.0 to 9.5 (Refs. 4, 178, 234, 236, 243). Besides activation by Ca2+ ions, the optimal concentration of which is 1 mM,234,236,244 strontium salts were also considered in the case of Bacillus sp. lyase.234 The enzyme from Pseudomonas sp. was also partly activated by magnesium chloride,178 and for the lyase of Clostridium felsineum, salts of other bivalent cations had an activating effect as well.245 (Ethylenedinitrilo)tetraacetic acid completely inactivated all of the lyases mentioned. The activity of endopectate lyase from Pseudomonas was also lessened in the presence of sodium chloride, potassium chloride, and dipotassium hydrogen phosphate (K2HP04). 

Hoshi, T., Zagotta, W. and Aldrich, R. W. Biophysical and molecular mechanisms of Shaker potassium channel inactivation. Science 250,533-538,1990. 

In contrast to the metabotropic effects described for presynaptic kainate receptors in CA1 (90,94), the effects of kainate in CA3 appear to be mediated by direct depolarization of the presynaptic terminals. The kainate-induced facilitation is not sensitive to antagonists of other receptors (e.g., GABAb), and can be mimicked by elevating the extracellular potassium concentration (77,100). It has been proposed that the facilitation is owing to increased calcium influx that is induced by modest depolarization of the terminals by kainate receptors, whereas a strong depolarization, in response to activation of a larger receptor population, causes the sodium channels to inactivate and thereby depresses transmission (77,84,88,100-102). 

BHT, potassium metabisulfite, PMSF and DTT are added just before homogenization, as these reagents readily inactivate. 

Armstrong, C.M. (1969) Inactivation of the potassium conductance and related phenomena caused by quaternary ammonium ion injection in squid axons. The Journal of General Physiology, 54, 553-575. 

Chen, J., Seebohm, G. and Sanguinetti, M.C. (2002) Position of aromatic residues in the S6 domain, not inactivation, dictates cisapride sensitivity of hERG and eag potassium channels. Proceedings of the National Academy of Sciences of the United States of America, 99, 12461-12466. 

Panyi, G. and Deutsch, C. (2007) Probing the cavity of the slow inactivated conformation of Shaker potassium channels. The Journal of General Physiology, 129, 403-418. 

The potassium sparing diuretic, amiloride (43), also produces a Class III effect in cardiac tissue. In canine Purkinje fibres APD is increased by 35% after prolonged exposure to 5 /zM of the drug [121]. The authors suggest two potential mechanisms for this effect (1) delay of inactivation of Na+ channels, or (2) inhibition of Na+/Ca + exchange. In infarcted dogs which were subjected to a PES protocol to produce re-entrant ventricular arrhyth-... 

Outward repolarizing currents oppose the effect of the inward Ica on the plateau phase. This current is carried predominantly through delayed rectifier potassium channels (Ik).These channels are voltage sensitive, with slow inactivation kinetics. Three distinct subpopulations of Ik with differing activation and inactivation kinetics have been described. A rapidly activating subset (Ikf), a slowly inactivating subset (Iks), and an ul-tra-rapidly activating subset to date are identified only in atrial tissue (Ikui)-... 

In normal atrial and ventricular myocytes, phase 4 is electrically stable, with the resting membrane potential held at approximately -90 mV and maintained by the outward potassium leak current and ion exchangers previously described. It is during phase 4 that the Na+ channels necessary for atrial and ventricular myocyte depolarization recover completely from inactivation. In myocytes capable of automaticity, the membrane potential slowly depolarizes during this period to initiate an action potential (discussed later). 

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