scholarly journals K+ Transport by the OsHKT2;4 Transporter from Rice with Atypical Na+ Transport Properties and Competition in Permeation of K+ over Mg2+ and Ca2+ Ions

2011 ◽  
Vol 156 (3) ◽  
pp. 1493-1507 ◽  
Author(s):  
Tomoaki Horie ◽  
Dennis E. Brodsky ◽  
Alex Costa ◽  
Toshiyuki Kaneko ◽  
Fiorella Lo Schiavo ◽  
...  
Keyword(s):  
Transport Properties ◽  
Na Transport ◽  
K Transport

scholarly journals The transition from HK to LK phenotype in the red cells of newborn genetically LK lambs.

1982 ◽  
Vol 79 (5) ◽  
pp. 893-915 ◽  
Author(s):  
E M Tucker ◽  
C E Smalley ◽  
J C Ellory ◽  
P B Dunham
Keyword(s):  
Transport Properties ◽  
Developmental Process ◽  
Fetal Hemoglobin ◽  
Kinetic Studies ◽  
Red Cells ◽  
Small Cells ◽  
Adult Hemoglobin ◽  
K Concentration ◽  
Cell Volumes ◽  
K Transport

Red cells from newborn lambs were separated into different age populations by centrifugation, and cells with fetal hemoglobin (Hb) were distinguished from those with adult Hb by an acid elution technique. Changes were followed during development in rates of K+ transport (active and passive), numbers of Na+/K+ pump sites per cell, cell volumes, and numbers of Lp and L1 antigen sites per cell. These changes were correlated with the percentage of cells with adult hemoglobin. (The Lp and L1 antigens are associated with K+ transport in that specific alloantibody against Lp, anti-Lp, stimulates active transport, and anti-L1 inhibits passive transport.) Active K+ transport decreased during development because of a decline in number of Na+/K+ pumps (from measurements of ouabain binding) and because of an alteration in the affinity of the pumps for intracellular K+ (from kinetic studies in which the intracellular K+ concentration was varied). Cells with fetal Hb had fewer Lp sites and were larger than cells with adult Hb. As transport properties changed, the number of Lp sites increased and continued to increase after all the cells had adult Hb Cells with fetal Hb had as many L1 sites as lamb cells with adult Hb, but the number of L1 sites was less than those found previously for adult sheep. A population of small cells with intermediate K+ concentration and intermediate numbers of Lp sites appeared soon after birth. The various points of evidence suggested that the developmental process leading to cells with adult transport properties was a gradual one and did not coincide precisely with the switch from fetal to adult Hb.

scholarly journals Na+ and K+ transport at basolateral membranes of epithelial cells. I. Stoichiometry of the Na,K-ATPase.

1986 ◽  
Vol 87 (3) ◽  
pp. 467-483 ◽  
Author(s):  
T C Cox ◽  
S I Helman
Keyword(s):  
Short Circuit ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
Ringer Solution ◽  
Na Transport ◽  
Basolateral Membranes ◽  
Dependent Component ◽  
Epithelial Sheets ◽  
Apical Membranes ◽  
K Transport

The stoichiometry of pump-mediated Na/K exchange was studied in isolated epithelial sheets of frog skin. 42K influx across basolateral membranes was measured with tissues in a steady state and incubated in either beakers or in chambers. The short-circuit current provided estimates of Na+ influx at the apical membranes of the cells. 42K influx of tissues bathed in Cl- or SO4-Ringer solution averaged approximately 8 microA/cm2. Ouabain inhibited 94% of the 42K influx. Furosemide was without effect on pre-ouabain-treated tissues but inhibited a ouabain-induced and Cl--dependent component of 42K influx. After taking into account the contribution of the Na+ load to the pump by way of basolateral membrane recycling of Na+, the stoichiometry was found to increase from approximately 2 to 6 as the pump-mediated Na+ transport rate increased from 10 to 70 microA/cm2. Extrapolation of the data to low rates of Na+ transport (less than 10 microA/cm2) indicated that the stoichiometry would be in the vicinity of 3:2. As pump-mediated K+ influx saturates with increasing rates of Na+ transport, Na+ efflux cannot be obligatorily coupled to K+ influx at all rates of transepithelial Na+ transport. These results are similar to those of Mullins and Brinley (1969. Journal of General Physiology. 53:504-740) in studies of the squid axon.

Active Transport of Potassium and Oxygen Consumption in the Isolated Midgut of Hyalophora Cecropia

1967 ◽  
Vol 46 (2) ◽  
pp. 235-248
Author(s):  
W. R. HARVEY ◽  
J. A. HASKELL ◽  
K. ZERAHN
Keyword(s):  
Oxygen Consumption ◽  
Oxygen Uptake ◽  
Active Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Na Transport ◽  
Maximum Value ◽  
Flux Measurements ◽  
Hyalophora Cecropia ◽  
K Transport

1. Flux measurements with 42K reveal that in the isolated midgut of Hyalophora cecropia 90 to 100 % of the short-circuit current is carried by the active transport of potassium from the blood-side to the lumen. 2. When K-transport is strongly depressed, either by withholding potassium from the blood side or by imposing a large positive potential on the lumen, the oxygen uptake of the isolated gut remains virtually unchanged. If the K-transport were to be energized by the negligible increase in oxygen uptake about 40 µ-equiv. of potassium would have to be transported for every µ-equiv. of extra oxygen taken up. This ratio of K-transport to oxygen uptake is thermodynamically impossible. 3. The ratio of potassium transported to total oxygen consumed when the midgut is bathed with 32 mM potassium on both sides is about 1.3 at temperatures of 25° and 15° C. The ratio must be smaller at lower potassium concentrations and is 2.0 at 73.5 mM-K, which may be approaching the maximum value. 4. Although the oxygen uptake is independent of the K-transport, the reverse is not true. There is a close dependency of K-transport on oxygen consumption. 5. K-transport by the midgut contrasts with Na-transport by the frog skin because Na-transport stimulates oxidative metabolism whereas K-transport does not. Evidently the coupling of transport to energy supply is different in the two systems.

K+ transport and its relation to Na+ transport in distal tubule of the hydrated dog

1971 ◽  
Vol 221 (5) ◽  
pp. 1456-1463 ◽  
Author(s):  
T Kahn ◽  
MH Goldstein ◽  
E Alfago ◽  
MF Levitt
Keyword(s):  
Distal Tubule ◽  
Na Transport ◽  
K Transport

Thermodynamic analysis of active sodium and potassium transport in the frog corneal epithelium

1982 ◽  
Vol 242 (6) ◽  
pp. F690-F698
Author(s):  
O. A. Candia ◽  
P. S. Reinach
Keyword(s):  
Transport System ◽  
Corneal Epithelium ◽  
Consumption Rate ◽  
Ussing Chamber ◽  
Electrical Conductance ◽  
Potassium Transport ◽  
Metabolic Reaction ◽  
O2 Consumption ◽  
Na Transport ◽  
K Transport

The formalism of linear nonequilibrium thermodynamics for a three-flow system was applied to the isolated frog corneal epithelium to study the coupling between metabolism and the Na-K transport system across this layer. There is little or no net ion transport across the isolated frog corneal epithelium bathed in Na2SO4 Ringer. Addition of amphotericin B to the tear side solution increases apical membrane permeability, which results in a net Na transport (from tear to stroma) and a net K transport in the opposite direction. Corneas were mounted in a modified Ussing chamber that permitted the simultaneous measurements of electrical parameters and O2 consumption by means of Clark-type oxygen electrodes. The overall degree of coupling, q, of the Na-K transport system to metabolism was calculated from measuring the suprabasal O2 consumption rate at "static head" and "level flow" conditions and by a second independent technique. Measurements of electrical conductance used in conjunction with other previously measured parameters allowed the calculation of the affinity, A, of the metabolic reaction driving transport, all phenomenological coefficients, and the electromotive forces of sodium (ENa) and potassium transport (EK). Values of q determined by the two techniques agreed (q = 0.80 and 0.84, respectively). This indicates incomplete coupling and a variable stoichiometric relationship among O2 consumption rate, net Na transport, and net K transport. The value calculated for A was 70.5 kcal.mol-1, for ENa 142.5 mV, and for EK -34.9 mV.

scholarly journals Passive potassium transport in LK sheep red cells. Effects of anti-L antibody and intracellular potassium.

1976 ◽  
Vol 68 (6) ◽  
pp. 567-581 ◽  
Author(s):  
P B Dunham
Keyword(s):  
Maximum Velocity ◽  
Red Cells ◽  
Na Transport ◽  
Sheep Red Cells ◽  
The Common ◽  
K Concentration ◽  
Mode Of Transport ◽  
Low K ◽  
K Transport ◽  
External K

The passive K influx in low K(LK) red blood cells of sheep saturates with increasing external K concentration, indicating that this mode of transport is mediated by membrane-associated sites. The passive K influx, iMLK, is inhibited by external Na. Isoimmune anti-L serum, known to stimulate active K transport in LK sheep red cells, inhibits iMLK about twofold. iMLK is affected by changes in intracellular K concentration, [K]i, in a complex fashion: increasing [K]i from near zero stimulates iMLK, while further increases in [K]i, above 3 mmol/liter cells, inhibit iMLK. The passive K influx is not mediated by K-K exchange diffusion. The effects of anti-L antibody and [K]i on passive cation transport are specific for K: neither factor affects passive Na transport. The common characteristics of passive and active K influx suggest that iMLK is mediated by inactive Na-K pump sites, and that the inability to translocate Na characterizes the inactive pumps. Anti-L antibody stimulates the K pump in reticulocytes of LK sheep. However, anti-L has no effect on iMLK in these cells, apparently because reticulocytes do not have the inactive pump sites which, in mature LK cells, are a consequence of the process of maturation of circulating LK cells. The results also indicate that anti-L alters the maximum velocity of both active and passive K fluxes by converting pumps sites from a form mediating passive K influx to an actively transporting form.

scholarly journals K+ transport properties of K+ channels in the plasma membrane of Vicia faba guard cells.

1988 ◽  
Vol 92 (5) ◽  
pp. 667-683 ◽  
Author(s):  
J I Schroeder
Keyword(s):  
Plasma Membrane ◽  
Transport Properties ◽  
Vicia Faba ◽  
Guard Cell ◽  
Guard Cells ◽  
Stomatal Opening ◽  
Whole Cell ◽  
K Channels ◽  
K Transport ◽  
K Currents

Electrical properties of the plasma membrane of guard cell protoplasts isolated from stomates of Vicia faba leaves were studied by application of the whole-cell configuration of the patch-clamp technique. The two types of K+ currents that have recently been identified in guard cells may allow efflux of K+ during stomatal closing, and uptake of K+ during stomatal opening (Schroeder et al., 1987). A detailed characterization of ion transport properties of the inward-rectifying (IK+,in) and the outward-rectifying (IK+,out) K+ conductance is presented here. The permeability ratios of IK+,in and IK+,out currents for K+ over monovalent alkali metal ions were determined. The resulting permeability sequences (PK+ greater than PRb+ greater than PNa+ greater than PLi+ much greater than PCs+) corresponded closely to the ion specificity of guard cell movements in V. faba. Neither K+ currents exhibited significant inactivation when K+ channels were activated for prolonged periods (greater than 10 min). The absence of inactivation may permit long durations of K+ fluxes, which occur during guard cell movements. Activation potentials of inward K+ currents were not shifted when external K+ concentrations were changed. This differs strongly from the behavior of inward-rectifying K+ channels in animal tissue. Blue light and fusicoccin induce hyperpolarization by stimulation of an electrogenic pump. From slow-whole-cell recordings it was concluded that electrogenic pumps require cytoplasmic substrates for full activation and that the magnitude of the pump current is sufficient to drive K+ uptake through IK+,in channels. First, direct evidence was gained for the hypothesis that IK+,in channels are a molecular pathway for K+ accumulation by the finding that IK+,in was blocked by Al3+ ions, which are known to inhibit stomatal opening but not closing. The results presented in this study strongly support a prominent role for IK+,in and IK+,out channels in K+ transport across the plasma membrane of guard cells.

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