Potassium transport

Pitman, M.G. Saddler, H.D. W. (1967). Active sodium and potassium transport in cells of barley roots. Proceedings of the National Academy of Sciences, USA, 57, 44-9. 

Potassium tetraperoxochromate(V), 6 536 Potassium tetrathiotungstate, 25 385 Potassium thiobismuthateCIII), 4 24 Potassium thiocyanate, 10 640 23 680 Potassium titanates, 25 43—44 Potassium toluenesulfonate, cosmetic surfactant, 7 834t Potassium transport, 20 641... 

O. A. Candia and P. S. Reinach. Thermodynamic analysis of active sodium and potassium transport in the frog corneal epithelium. Am J Physiol 242 F690-F698 (1982)... 

Evans, L. S., and I. P. Ting. Effect of ozone on "Rb-labeled potassium transport in leaves of Phaseolus vulgaris L. Atmos. Environ. 8 855-861, 1974. 

This class of enzymes [EC 3.6.1.36] (also known as the hydrogen/potassium-exchanging ATPase, the potassium-transporting ATPase, proton pump, and the gastric H+/K+ ATPase) catalyzes the hydrolysis of ATP to ADP and orthophosphate, coupled with the exchange of and ions. The gastric mucosal enzyme has been the best characterized. 

Mulet JM, Leube MP, Kron SJ, Rios G, Fink GR, Serrano R (1999) A novel mechanism of ion homeostasis and salt tolerance in yeast the Hal4 and Hal5 protein kinases modulate the Trkl-Trk2 potassium transporter. Mol Cell Biol 19 3328-3337... 

Digitalis acts by interfering with the sodium and potassium transport across the cell membrane and by increasing the amount of coupling calcium i.e. making more calcium available for excitation-contraction coupling. 

In contrast to the hydrolysis and synthesis of ATP connected with proton translocation in mitochondria, chloroplasts and bacterial membranes, the energy linked movement of calcium ions gives rise to the appearance of an acid-stable phosphorylated intermediate in the membranes. A cation specific phosphorylation also occurs in the membranes of the sodium potassium transport system183. However, due to the inability to correlate phosphorylation and ion movement in the latter membranes, membrane phosphorylation has been questioned as being a step in the reaction sequence of ion translocation184,18s. Solely the sarcoplasmic calcium transport system allows to correlate directly and quantitatively ion translocation with the phosphoryl transfer reactions. 

Uncomplexed valinomycin has a more extended conformation than it does in the potassium complex.385,386 The conformational change results in the breaking of a pair of hydrogen bonds and formation of new hydrogen bonds as the molecule folds around the potassium ion. Valinomycin facilitates potassium transport in a passive manner. However, there are cyclic changes between two conformations as the carrier complexes with ions, diffuses across the membrane, and releases ions on the other side. Tire rate of transport is rapid, with each valinomycin molecule being able to carry 104 potassium ions per second across a membrane. Tlius, a very small amount of this ionophore is sufficient to alter the permeability and the conductance of a membrane. 

The uptake of potassium by microorganisms has been well studied. In the case of E. coli, kinetic investigations on different strains have demonstrated the presence of three or four transport systems. The presence of inducible pathways with widely different Km values for binding K+ allows the cell to accumulate K+ to a constant level under different environments. These transport pathways include those linked to the proton circuit and an example linked to a pump and ATP hydrolysis. Thus the Kdp system is a high affinity pathway with Km = 1 mol dm-3, and involves three proteins in the inner membrane of E. coli, including a K+-stimulated membrane ATPase. The KHA (i.e. K+-H+ antiport) path is driven by proton motive force, while the low affinity system TrKA depends on both ATP and the proton motive force.80,81,82 S. cerevisiae accumulates K+ by K+/H+ exchange.83 Potassium transport may thus be used to control intracellular pH. 

As a final example, it should be noted that in the presence of valinomycin, K+ is taken up by mitochondria to compensate for the H+ lost in forming the proton gradient. This work confirms the ratio of four K+ taken up per pair of electrons passing the energy-conserving site and so is equivalent to the H+/site ratio.85 The protein responsible for K+/H+ antiport has been identified.86 Other potassium transport processes have been described.87... 

FIGURE 22.6 Permeability and permselectivity of vaginal and buccal epithelia in the rabbit, (a) Flux of 6-carboxyfluoroscein, a hydrophilic molecule, by in vitro perfusion studies steady-state flux ( xg/cm2/h x 106), (b) resistance (fl cm2 x 10 2), (c) thickness (p,m x 10-2), and (d) ratio of potassium transport number to chloride transport number, which is calculated from electrical measurements, used as indicative of the epithelium selectivity for positively charged molecules. (Modified from Sayani, A.P. and Chien, Y.W., Crit. Rev. Ther. Drug Carrier Syst. 13, 85, 1996.)... 

Mathematical derivations of potassium transport and transformation processes may be formulated as follows. The following new terms can be defined C, concentration of potassium in solution phase Si, amount of potassium in exchangeable phase S2, amount of potassium in nonexchangeable phase S5, amount of potassium in primary mineral phase wPW, pore water velocity Dc, dispersion coefficient and d, depth or distance below soil surface. 

One in vitro study on rat renal tissue homogenate showed barium weakly inhibited the sodium-potassium-adenosine triphosphatase enzyme system (Kramer et al. 1986). A second study on mouse kidney tubules showed barium chloride could depolarize the membrane and inhibit potassium transport (Volkl et al. 1987). A similar defect in cell membrane transport in humans could be responsible for the renal involvement observed in some cases of acute barium poisoning. 

Barbiturates are thought to interfere with sodium and potassium transport across cell membranes. This leads to inhibition of the mesencephalic reticular activating system. Polysynaptic transmission is inhibited in all areas of the CNS. Barbiturates also potentiate GABA action on chloride entry into the neuron, although they do not bind at the benzodiazepine receptor. 

Ritchie, R. J., andLarkum, A. W. D. (1985a). Potassium transport in Enteromorpha intestinalis (L.) Link. 

The hydrated thallous ion is similar in size to the hydrated potassium ion, and early literature reported that the uptake of T1 cations in muscle cells made use of the specific uptake mechanism developed for potassium. However, later studies, taking account of the complexity of potassium transport, and the different types of potassium channels, have found some differences between the cellular T1 uptake and the potassium uptake. Thus, digoxin that inhibits the Na/K ATP-ase enzyme system as well as the potassium ion-transport, did not affect the ° T1 transport. 

Sen, A. K., Post, R. L. Stoichiometry and locahzation of adenosine triphosphate-dependent sodium and potassium transport in the erythrocyte. J. Biol. Chem. 1964,239, 345-352. 

Hyperkalemia is more common in patients with Stage 5 CKD therefore the discussion of treatment options focuses on interventions in this population. The majority of patients can be managed with a dietary potassium restriction of 50 to 80 mEq/day and alterations in dialysate potassium concentrations for patients receiving hemodialysis or peritoneal dialysis. Hyperkalemia is less common, however, in the peritoneal dialysis population due to differences in potassium transport. Constipation in patients with CKD can interfere with colonic potassium excretion therefore a good bowel regimen is important. For severe hyperkalemia hemodialysis is often required using a low-potassium dialysate bath (see Chap. 50). 

Inflamrnation NeiJtroplifl activation 8- Trsnsport.Potassium transport... 

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