Membrane Cholesterol Depletion and K+Transport in High and Low Potassium Sheep Red Cells

1980 ◽  
Vol 3 (1-2) ◽  
pp. 21-35 ◽  
Author(s):  
J. E. Grey ◽  
P. K. Lauf
Keyword(s):  
Red Cells ◽  
Membrane Cholesterol ◽  
Cholesterol Depletion ◽  
Sheep Red Cells ◽  
Low Potassium ◽  
K Transport

scholarly journals Active Sodium and Potassium Transport in High Potassium and Low Potassium Sheep Red Cells

1971 ◽  
Vol 58 (4) ◽  
pp. 438-466 ◽  
Author(s):  
P. G. Hoffman ◽  
D. C. Tosteson
Keyword(s):  
Cell Types ◽  
Red Cells ◽  
Kinetic Characteristics ◽  
High Potassium ◽  
Cation Composition ◽  
Sheep Red Cells ◽  
Pump Rate ◽  
Low Potassium ◽  
K Transport ◽  
External K

The kinetic characteristics of the ouabain-sensitive (Na + K) transport system (pump) of high potassium (HK) and low potassium (LK) sheep red cells have been investigated. In sodium medium, the curve relating pump rate to external K is sigmoid with half maximal stimulation (K1/2) occurring at 3 mM for both cell types, the maximum pump rate in HK cells being about four times that in LK cells. In sodium-free media, both HK and LK pumps are adequately described by the Michaelis-Menten equation, but the K1/2 for HK cells is 0.6 ± 0.1 mM K, while that for LK is 0.2 ± 0.05 mM K. When the internal Na and K content of the cells was varied by the PCMBS method, it was found that the pump rate of HK cells showed a gradual increase from zero at very low internal Na to a maximum when internal K was reduced to nearly zero (100% Na). In LK cells, on the other hand, no pump activity was detected if Na constituted less than 70% of the total (Na + K) in the cell. Increasing Na from 70 to nearly 100% of the internal cation composition, however, resulted in an exponential increase in pump rate in these cells to about ⅙ the maximum rate observed in HK cells. While changes in internal composition altered the pump rate at saturating concentrations of external K, it had no effect on the apparent affinity of the pumps for external K. These results lead us to conclude that the individual pump sites in the HK and LK sheep red cell membranes must be different. Moreover, we believe that these data contribute significantly to defining the types of mechanism which can account for the kinetic characteristics of (Na + K) transport in sheep red cells and perhaps in other systems.

Swelling, NEM, and A23187 activate Cl(-)-dependent K+ transport in high-K+ sheep red cells

1987 ◽  
Vol 252 (2) ◽  
pp. C197-C204 ◽  
Author(s):  
H. Fujise ◽  
P. K. Lauf
Keyword(s):  
Metal Ion ◽  
Red Cells ◽  
Common Mechanism ◽  
Ionophore A23187 ◽  
Sheep Red Cells ◽  
High K ◽  
Sh Group ◽  
Low K ◽  
K Transport ◽  
Significant Activation

In low K+ (LK) sheep red cells a significant fraction of the total ouabain-resistant (OR) K+ flux is inhibited when Cl- is replaced by other anions of the Hofmeister series except Br- (Cl(-)-dependent K+ flux). In contrast, high K+ (HK) sheep red cells in isosmotic media did not possess any significant OR Cl(-)-dependent K+ flux when Cl- was replaced by NO3- or I-. However, exposure to hyposmotic solutions, treatment with the sulfhydryl (SH) group reagent N-ethylmaleimide (NEM) or with the bivalent metal ion (Me2+) ionophore A23187 in absence of external Me2+ caused a significant activation of Cl(-)-dependent K+ transport as measured with Rb+ as K+ congener. There was no Cl(-)-dependent Rb+ flux in A23187-treated cells when Mn2+, Mg2+, and Ca2+ were present at 1 mM concentrations, suggesting that cellular accumulation of these Me2+ is inhibitory. Similar to LK red cells, HK red cells failed to respond to A23187 when pretreated with NEM supporting the hypothesis proposed recently (Lauf, P. K. J. Membr. Biol. 88: 1-13, 1985) of a common mechanism of Cl(-)-dependent K+ transport activation. The magnitudes of the Cl(-)-dependent Rb+ fluxes in HK cells were much smaller than those elicited by identical treatments in LK red cells, and the effect of all interventions was not due to the presence of reticulocytes known to possess Cl(-)-dependent K+ transport.(ABSTRACT TRUNCATED AT 250 WORDS)

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 Activation of Membrane Cholesterol by Displacement from Phospholipids

2005 ◽  
Vol 280 (43) ◽  
pp. 36126-36131 ◽  
Author(s):  
Yvonne Lange ◽  
Jin Ye ◽  
Theodore L. Steck
Keyword(s):  
Cholesterol Oxidase ◽  
Human Fibroblasts ◽  
Red Cells ◽  
Membrane Cholesterol ◽  
Cholesterol Depletion ◽  
Membrane Phospholipids ◽  
Equilibrium Partition ◽  
Coa Reductase ◽  
Intercalating Agents ◽  
Hydroxymethylglutaryl Coa Reductase

We tested the hypothesis that certain membrane-intercalating agents increase the chemical activity of cholesterol by displacing it from its low activity association with phospholipids. Octanol, 1,2-dioctanoyl-sn-glycerol (a diglyceride), and N-hexanoyl-d-erythrosphingosine (a ceramide) were shown to increase both the rate of transfer and the extent of equilibrium partition of human red blood cell cholesterol to methyl-β-cyclodextrin. These agents also promoted the interaction of the sterol with two cholesterol-specific probes, cholesterol oxidase and saponin. Expanding the pool of bilayer phospholipids with lysophosphatides countered these effects. The three intercalators also protected the red cells against lysis by cholesterol depletion as if substituting for the extracted sterol. As is the case for excess plasma membrane cholesterol, treating human fibroblasts with octanol, diglyceride, or ceramide stimulated the rapid inactivation of their hydroxymethylglutaryl-CoA reductase, presumably through an increase in the pool of endoplasmic reticulum cholesterol. These data supported the stated hypothesis and point to competition between cholesterol and endogenous and exogenous intercalators for association with membrane phospholipids. We also describe simple screens using red cells in a microtiter well format to identify intercalating agents that increase or decrease the activity of membrane cholesterol.

Identification of a 25 kDa polypeptide associated with the L antigen in low potassium-type sheep red cells

1990 ◽  
Vol 1022 (3) ◽  
pp. 408-410 ◽  
Author(s):  
Steven J. Pittman ◽  
J.Clive Ellory ◽  
Elizabeth M. Tucker ◽  
Christopher I. Newbold
Keyword(s):  
Red Cells ◽  
Sheep Red Cells ◽  
Low Potassium
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