Potassium fluxes

Talaromycin B is a spiro-acetal produced by the fungus Talaromyces stipitatus, the toxicity of which may be due to its ability to block outward potassium fluxes. In an elegant synthesis, the requisite open-chain polyol with hydroxy groups in the y-and y -positions was assembled from nitrile oxide and olefin building blocks 50 and 51, both of which carry a f>w(hydroxyethyl) moiety protected as a cyclohexanone acetal (284). Hydrogenolysis of the N O bond of isoxazoline 52 using Raney nickel, followed by treatment with aqueous acid, gave the spiroketal 53, which was further transformed into racemic talaromycin B (54) (Scheme 6.54) (284). 

This instrument has allowed several studies that provide information not obtainable by other means to be conducted. Four examples are presented as follows The first example concerns the question of the mechanism of emission of potassium ions from potassium zeolite [7]. Earlier studies had made the assumption that this was an S-L type of ion formation mechanism [8], implying that there was a neutral potassium atom flux accompanying the flux of atomic potassium cations. Experiments performed on this instrument clearly showed that this is not the case there was no detectable neutral atomic potassium flux accompanying the cation flux. Thus this instrument was used to answer a long-standing question with an experiment conducted in one afternoon and allowed the conclusion to be reached that the mechanism is potassium ions in the solid state subliming into the gas phase. 

Z7. Zierler, K. L., Potassium flux and further observations on aldolase flux in dystrophic mouse muscle. Bull. Johns Hopkins Hosp. 108, 208 (1961). 

The cause of the pain is unknown, although there are many hypotheses such as damage to muscle (43,44) resulting from asynchronous contractions of adjacent muscle fibers (45), irreversible damage to muscle spindles (46), potassium flux (47), lactic acid (48), serotonin (49), calcium influx-associated damage to muscle spindles (50), and prostaglandins (51,52). The pain appears not to be related to the extent or intensity of the observed fasciculations. 

The major effect is on the distal tubules of nephrons, where aldosterone promotes sodium retention and potassium excretion. Under the influence of aldosterone, sodium ions are actively transported out of the distal tubular cell into blood, and this transport is coupled to passive potassium flux in the opposite direction. Consequently, intracellular [Na" ] is diminished and intracellular [K+] is elevated. This intracellular diminution of [Na+] promotes the diffusion of sodium from the filtrate into the cell, and potassium diffuses into the filtrate. Aldosterone also stimulates sodium reabsorption from salivary fluid in the salivary gland and from luminal fluid in the intestines, but these sodium-conserving actions are of minor importance. 

Bogdanova A, Nikinmaa M. 2001. Reactive oxygen species regulate oxygen-sensitive potassium flux in rainbow trout erythrocytes. J Gen Physiol 117 181-190. 

Fig. 2. Schematic of the physiological process and potassium fluxes that underlie the ERG. In the dark (left panel), the rod photoreceptor sustains a cunent circulating from tire outer to inner segment via a gated cationic channel. Stacked membrane discs hold the light labile photopigment. After light activates tire photopigment (right panel), a series of cascade events take place to close the cationic channels see text). This reduces the daik cun ent and results in the fast PHI component of the ERG that produces the leading edge of the a-wave.

Kline RP. Ripps H, Dowling JE. Light induced potassium fluxes in the skate retina. J Neurosci 1985 464 225-235. 

Carmeliet, E. E., Lieberman, M. Pflueger s Arch. 358 (3), 243 (1975). Increase of potassium flux by valinomycin in embryonic chick heart... 

These drugs mediate an increase in potassium flux, due to an increase in the number of opening potassium channels. A decrease in calcium flux is also seen, due to the closing of membrane calcium channels. 

In low therapeutic doses, the drug produces a decrease in conduction rate through receptor blockade and an increase in outward potassium flux. In high doses, the drug depresses sodium permeability, causing a local, anesthetic-like effect. 

Phase 2 of the cardiac action potential is prolonged, due to the blockade of potassium flux decreasing the excitability of tissue and thus inhibiting the spontaneous formation of ectopic foci. 

To the extent that sodium flux is increased, potassium flux may also be decreased. However, the drug has a substantially decreased effect on the blockade of outward potassium current, as compared to that of sodium. 

I. Mechanism of toxicity. The mechanism of thallium toxicity is not known. It appears to affect a variety of enzyme systems, resulting in generalized cellular poisoning. Thallium metabolism has some similarities to that of potassium, and it may inhibit potassium flux across biological membranes by binding to Na-K ATP transport enzymes. 

Low concentrations of polyenes, other than filipin, produced more subtle effects on the erythrocyte membrane. Amphotericin B treatment elicited potassium fluxes from erythrocytes [119]. The influence of amphotericin B upon the permeability of mammalian erythrocytes has been studied by measuring move-... 

It is well known that the resting and dynamic electrical activity of the brain is a consequence of electrochemical potentials across membranes. Many other aspects of electrochemistry are also familiar in the neurosciences. Hence it may seem paradoxical to have suggested that the electro-analytical techniques are far afield of the mainstream of neurobiology. However, neuronal membrane potentials depend on ionic charge distributions and fluxes insofar as is known, electron current plays no role. Just the opposite is true for electroanalytical techniques—ionic conductance is of minimal importance but electron flow (current) is the essence of the measurement. The electrodes employed do not sense membrane potentials or respond to sodium or potassium fluxes rather, they pass small but finite currents because molecules close to their surface undergo oxidation or reduction. Such electrochemical measurements are called faradaic (because the amount of material converted at the electrode surface can be calculated from Faraday s law). 

When he measured potassium fluxes, Villegas considered the mucosa to be a single semipermeable membrane. With the concentration of potassium the same on each side, the flux equation reduces to... 

Electrophysiology of Secretion Warren S. Rehm, 56 Electrolyte Composition of the Gastric Mucosa, 59 Chloride Transport by Isolated Oxyntic Cells, 62 Asymmetry of the Gastric Mucosa, 64 Identification of Potassium Fluxes, 67 Thiocyanate Again, 67... 

Davies, D.D. Organic acid metabolism in plants. Biol. Rev. 34,407-444 (1959) Dayanandan,P., Kaufman, P.B. Stomatal movements associated with potassium fluxes. Am. . Bot. 62,221-231 (1975)... 

Toxicants that affect sodium or potassium flux (e.g., DDT, pyrethrins) often cause sud> den and dramatic dinlcal signs characterized by changes in nerve electrical activity. 

The effect could be significant only if the CEC of the montmorillonite is saturated with potassium during the maximum temperature pulse (temperatures >110°C are necessary) but this is excluded due to the low potassium flux at the proposed site (see comments above). In addition, the heat pulse will, in any case, coincide with the... 

In terms of potential perturbations to the EBS, the greatest effects are those which have an impact on the bentonite. Careful siting of the repository will remove most, such as illitization due to a high potassium flux, and most others identified to date are unlikely to have a significant impact on repository performance. Some open questions remain on other potential perturbations, the answers to which would increase confidence in the performance of the repository. These include ... 

---