PubMed Health⌕ Search

Biomedical subjects

J Duhm

Publications and source records attributed to J Duhm.

At least 19 recordsLinked to original sources
PubMed1992

Changes of membrane phospholipid composition of human erythrocytes in hyperlipidemias. I. Increased phosphatidylcholine and reduced sphingomyelin in patients with elevated levels of triacylglycerol-rich lipoproteins.

The composition of red blood cell membrane and plasma phospholipids has been analyzed in patients with hyperlipidemias. In red cells of patients with elevated levels of triacylglycerol-rich lipoproteins, phosphatidylcholine (PC) was raised and sphingomyelin (SM) reduced, resulting in a 20% increase of the membrane PC/SM ratio. In plasma phospholipids of these patients PC and SM levels were also higher and lower, respectively and the plasma PC/SM ratio was elevated by more than 50%. Close positive correlations between plasma and membrane phospholipids were obtained for PC, SM and the PC/SM ratio in normolipidemic and hyperlipidemic donors. Plasmalogen phosphatidylethanolamine (PE), a supposed endogenous protector against lipid oxidation, was reduced by about 20% in red cell membrane lipids in hyperlipidemic patients. Also plasmalogen-PE in plasma tended to be reduced in hyperlipidemic donors. Plasma HDL levels were positively related to the content of plasmalogen PE in the red cell membrane. In conclusion, there are closely related increases in PC/SM ratios in plasma and the red cell membrane in patients with elevated levels of triacylglycerol-rich lipoproteins. It is speculated that decreases in red cell membrane plasmalogen-PE in hyperlipidemic patients could be related to impaired antioxidant protection, possibly as a consequence of reductions in plasma HDL levels.

Adult↗
PubMed1992

Changes of membrane phospholipid composition of human erythrocytes in hyperlipidemias. II. Increases in distinct molecular species of phosphatidylethanolamine and phosphatidylcholine containing arachidonic acid.

The molecular species composition of red blood cell diacyl-phosphatidylcholine (PC), diacyl-phosphatidylethanolamine (PE) and alkenylacyl-PE (plasmalogen PE) has been analyzed in normolipidemic and hyperlipidemic donors. In all three phospholipid subclasses the percentages of the species 16:0/20:4 were increased in hyperlipidemic patients. In diacyl-PE, 18:1/20:4 was also elevated. No changes were observed in the other quantitatively important molecular species containing arachidonic acid at sn-2, namely 18:0/20:4. The rise in 16:0/20:4 in diacyl-PC and diacyl-PE of hyperlipidemic donors was accompanied by a fall in molecular species with linoleic acid (18:2) at sn-2 (in particular 18:1/18:2). In alkenylacyl-PE the elevation of 16:0/20:4 was compensated by a decrease in species with docosatetraenoic acid (22:4) at sn-2 in particular by a fall in 16:0/22:4. Among all donors, the percentages of 16:0/20:4 in diacyl-PC and PE were positively associated with plasma total cholesterol levels. The changes in molecular species composition of PC and PE in hyperlipidemia are expected to alter the function of erythrocyte membrane transport proteins and--if present also in other cell types--to affect eicosanoid metabolism.

Arachidonic Acids↗
PubMed1992

Epidermal growth factor stimulates Ca2+ uptake of human erythrocytes.

To examine the functional significance of epidermal growth factor (EGF) binding sites present on the human erythrocyte membrane [Engelmann et al. (1992) Am J Hematol 39:239-241], the effect of EGF on 45Ca2+ uptake and on 22Na+ efflux from these cells has been studied. In all cases media contained 1.25 mM Ca2+, whereas Na+ and K+ were varied. In 140 mM Na+/5 mM K+ medium EGF (250 ng/ml) stimulated 45Ca2+ uptake by 50%-90% in quin-2-loaded cells, and by up to threefold in untreated cells. Increasing extracellular K+ up to 75 mM at the expense of extracellular Na2+ stimulated the EGF-induced 45Ca2+ uptake by about twofold compared to 145 mM Na+ medium both in quin-2-loaded and in untreated cells. In 145 mM K+ medium, however, no EGF-induced 45Ca2+ uptake was detectable in quin-2-loaded cells, while in untreated cells Ca2+ entry was stimulated twofold by EGF. After increasing intracellular Na+ from 6 mmol/l cells to 18 mmol/l cells in untreated cells suspended in 145 mM K+ medium, 45Ca2+ uptake induced by EGF gradually increased. In contrast, in 140 mM Na+/5 mM K+ as well as in 70 mM Na+/75 mM K+ medium, 45Ca2+ uptake accelerated by EGF was largely unaffected by a modified red cell Na+ content. When 22Na-loaded untreated red cells were suspended in 145 mM K+ medium EGF stimulated red cell 22Na+ efflux by more than threefold. In 140 mM Na+/5 mM K+ as well as in 70 mM Na+/75 mM K+ medium, no 22Na+ efflux induced by the growth factor was evident.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminoquinolines↗
PubMed1991

Role of ABH blood group antigens in the stimulation of a DIDS-sensitive Ca2+ influx pathway in human erythrocytes by Ulex europaeus agglutinin I and a monoclonal anti A1 antibody.

Of eleven agglutinating lectins tested, only one, Ulex europaeus agglutinin I (UEA1), stimulated Ca2+ uptake in quin2-loaded erythrocytes by about 2-fold. UEA1 is known to be an alpha-L-fucose and ABH blood group specific lectin. The 45Ca2+ influx induced by UEA1 was absent in the presence of extracellular fucose (5 and 15 mM) and depended on the ABH blood group of the donor, the stimulatory potency of the lectin decreasing in the order H greater than A2 greater than A1. Ca2+ entry blockers, such as cobalt and verapamil, did not affect the 45Ca2+ influx induced by UEA1. 4,4'-Diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) inhibited dose-dependently with a Ki of 1-2 microM. 10 microM DIDS, 10 microM 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS) and 20 microM dipyridamole fully blocked the 45Ca2+ influx induced by UEA1. The effect of UEA1 on 45Ca2+ influx was absent in K+ and Mg2+ media and was less pronounced in choline than in Na+ media. The 45Ca2+ influx induced by the lectin was abolished by preincubation with 12-O-tetradecanoylphorbol 13-acetate (TPA, 60 ng/ml). A monoclonal antibody raised against A1 erythrocytes (Bric 54) accelerated 45Ca2+ influx in quin2 loaded A1 erythrocytes by about 2-fold. No effect was seen in A2 and H erythrocytes. The 45Ca2+ influx elicited by Bric 54 exhibited a sensitivity towards inhibition by DIDS and TPA, as well as a dependence on the cation composition of the incubation medium similar to that observed with UEA1. The effects of UEA1 and Bric 54 were not additive. These observations suggest that the Ca2+ influx induced by UEA1 and Bric 54 is mediated by the same transport pathway. Since both the lectin and the antibody exhibit ABH blood group specificity, it appears reasonable to conclude that ABH antigens can serve as recognition sites for activation of a Ca2+ influx pathway in human erythrocytes, which is sensitive to inhibitors of the band 3 anion-exchanger.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1991

Effect of cholesterol and dipalmitoyl phosphatidylcholine enrichment on the kinetics of Na-Li exchange of human erythrocytes.

The effects of cholesterol loading and depletion and of a 10% replacement of native phosphatidylcholine by dipalmitoyl phosphatidylcholine (di 16:0-PC) on kinetic properties of human red cell Na-Li exchange have been studied. Compared to control erythrocytes (cholesterol/phospholipid ratio (C/P = 0.8-0.9], Vmax of phloretin-sensitive Li uptake and of Li efflux stimulated by extracellular Na (Nao) were reduced by 15-30% in cholesterol-loaded red cells (C/P = 1.05-1.33). The apparent Km values for external Li (Lio) and for internal Li (Lii) were decreased by about one-third in these cells. Cholesterol depletion (C/P = 0.7) exerted opposite effects on the kinetics of Nao-dependent Li efflux. On augmenting C/P from 0.66 to 1.0, Vmax of Nao-dependent Li efflux was reduced by about 30%; increasing C/P above 1.0 caused no further lowering of Vmax.Li leakage rates monotonically decreased over the whole range of C/P ratios examined (0.66-1.3). This indicates that Na-Li exchange and Li leak are differentially affected by cholesterol. Incorporation of di 16:0-PC (replacement of 3% of total red cell phospholipids) caused similar kinetic alterations of Na-Li exchange as a rise in membrane cholesterol by 20-50%. Notably, selective incorporation of di 16:0-PC into the outer monolayer increased both intra- and extracellular Li binding affinities of Na-Li exchange and lowered its maximum velocity. Thus, both di 16:0-PC enrichment and cholesterol loading exerted an uncompetitive type of transport inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1990

Use of chlortetracycline fluorescence for the detection of Ca storing intracellular vesicles in normal human erythrocytes.

The uptake of chlortetracycline (CTC) and the nature of the fluorescence of CTC was studied in intact human erythrocytes from apparently healthy donors. The uptake of CTC at 22 degrees C proceeded with a t1/2 of about 3 min, and after 15 min a stable equilibrium was achieved with an intracellular accumulation by a factor of 5-6 relative to the medium concentration. The accumulation did not change in the range of CTC concentrations tested (20-500 microM). The Ca specificity of the CTC fluorescence spectrum was confirmed by Ca depletion of red cells using A23187 in the presence of EGTA and 0.2 mM Mg. This procedure decreased the total intracellular calcium content by about 70% and reduced the fluorescence intensity to one-fourth. Fluorescence microscopy of red cells incubated with 100 microM CTC at 22 degrees C showed that the fluorescence originated mainly from the red cell membrane. In addition, in about 15% of erythrocytes one or more fluorescent dots (diameter greater than 0.2 less than 1 microns) were detected. The fluorescence of the dots and membranes was related to calcium, as evidenced by the reduction of their intensity in Ca depleted cells. The number of erythrocytes with fluorescent dots and the frequency of the dots per cell was largely unaffected by lowering the incubation temperature to 0 degrees C, indicating that the dots most probably do not represent endocytotic artifacts induced by CTC. The number of dots was increased in erythrocytes preincubated with primaquine, demonstrating that CTC fluorescence can be applied to monitor the appearance of intracellular Ca storing vesicles. It is concluded that in (at least) 15% of erythrocytes obtained from apparently healthy donors intracellular vesicles containing Ca can be detected by CTC fluorescence microscopy.

Biological Transport↗
PubMed1990

Alterations in Na+, K+ and Ca2+ transport in erythrocytes of patients with carcinomas of the head and neck: possible role of mild anaemia and cell age.

1. Rates of erythrocyte Ca2+ inward transport, activities of erythrocyte Ca2(+)-adenosine triphosphatase, Na+, K+ pump, Na(+)-K+ co-transport and Na(+)-Li+ exchange, and erythrocyte Ca2+, K+ and Na+ contents have been determined in patients with carcinomas of the head and neck. 2. Decreases in Ca2+ inward transport and Na(+)-K+ co-transport activity, and increases in erythrocyte Ca2+ and K+ contents, were observed. 3. The more pronounced changes found in advanced carcinoma stages proved to be related to a 50% incidence of a mild anaemia of chronic disease in patients with carcinoma stages T3 and T4. 4. 'Young' (light) erythrocytes from healthy donors obtained by density centrifugation showed modifications in Na+ transport and K+ content similar to those seen in the patients. 5. It is concluded that the decrease in Na(+)-K+ co-transport activity, as well as the elevated K+ content and the lowered mean corpuscular haemoglobin content, but not the disturbances in Ca2+ homoeostasis, in erythrocytes of patients with carcinomas of the head and neck are most probably due to the occurrence of a mild anaemia of chronic disease in advanced carcinoma stages, associated with a reduction in mean erythrocyte age.

Adult↗
PubMed1990

Effects of a chronic high salt intake on blood pressure and the kinetics of sodium and potassium transport in erythrocytes of young and adult subtotally nephrectomized Sprague-Dawley rats.

Erythrocyte Na+ and K+ transport mediated by the Na(+)-K+ pump, the Na+,K+ cotransport system and cation leaks, together with blood pressure, were determined in young and adult rats subjected to either chronic salt deprivation or chronic salt loading combined with subtotal nephrectomy. The kinetics of ion transport were studied in Na+ media as a function of extracellular K+, replaced by extracellular Rb+, and intracellular Na+ varied around the physiological range. A high salt intake increased blood pressure in young but not in adult subtotally nephrectomized rats. Erythrocyte Na+ or K+ contents of salt-deprived and salt-loaded rats did not differ. There were no major changes in Na+,K+ cotransport or cation leaks in salt-loaded rats. Chronic salt loading caused some alterations in the kinetics of the Na(+)-K+ pump, which were greater in young than in adult rats. The most pronounced change was a decreased affinity of the Na(+)-K+ pump for intracellular Na+, which was partially balanced by an increased maximal velocity. At physiological (in vivo) ion concentrations these kinetic alterations caused a slight reduction in total ouabain-sensitive Rb+ uptake [partly due to a decrease in intracellular K+:extracellular Rb+ (1:1) exchange] but no changes in Na+ net extrusion in salt-loaded rats. The erythrocyte Na+ and K+ transport systems showed no changes in intrinsic properties that would favour the development or maintenance of salt hypertension in young over adult rats if similar alterations occurred in tissues relevant for blood pressure control.

Age Factors↗
PubMed1990

Kinetics of Na+ and K+ transport in red blood cells of Dahl rats. Effects of age and salt.

Blood pressure response to chronic high salt intake and kinetics of red blood cell Na+ and K+ (Rb+) transport were studied in salt-sensitive (DS) and salt-resistant (DR) Dahl rats fed a high salt diet (8% NaCl) for 7 weeks from the fifth (young), 12th (adult), or 23rd (old) week of age. The kinetics of ouabain-sensitive Rb+ uptake and Na+ extrusion were determined in Na+ media as a function of both intracellular Na+ (Na+i, 2-8 mmol/l cells) and extracellular Rb+ (Rb+o). In addition, the kinetics of furosemide-sensitive Rb+ uptake (related to Rb+o) and the magnitude of the Na+ and Rb+ leaks were assessed. High salt induced hypertension in young and adult but not in old DS rats although red blood cell Na+ was slightly increased in all age groups of DS rats fed a high salt diet. The kinetic parameters of the Na(+)-K+ pump were similar in DS and DR rats fed a low salt diet. Ouabain-sensitive transport rates were not suppressed in erythrocytes of salt hypertensive Dahl rats. Maximal velocities of the Na(+)-K+ pump (related to Na+i) decreased significantly with age in all groups except in DS rats fed a high salt diet. This was compensated by an age-dependent increase in the affinity for Na+i so that no substantial differences in transport rates between young and old rats were seen at physiological cell Na+ and plasma K+ levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1990

Kinetics of red cell Na+ and K+ transport in Prague hypertensive rats.

Kinetics of ouabain-sensitive, furosemide-sensitive (FS), bumetanide-sensitive (BS) and -resistant Na+ and K+ transport were studied in erythrocytes of Prague hypertensive rats (PHR) and Prague normotensive rats (PNR). Maximal transport rates (Vmax) and apparent affinities for either intracellular Na+ or extracellular K+ (replaced by Rb+) were determined in red cells in which Na+ content varied around the physiological range and that were incubated in Na+ media. No major differences between PHR and PNR were disclosed in the kinetics of ion transport mediated by the Na(+)-K+ pump or BS inward Na(+)-K+ cotransport. FS Rb+ uptake was higher (due to a greater Vmax) in red cells of PHR as compared to PNR. In cells with a lowered Na+ content this elevation of FS Rb+ uptake was largely due to an augmented K(+)-Cl- cotransport which exhibits a low affinity for Rb+o and is blocked by 1 mM furosemide but not by 10 microM bumetanide. Red cells of PHR and PNR strains did not differ in either Na+ or Rb+ leaks. A slight increase of red cell Na+ content in PHR was evaluated in terms of the pump-leak concept. The present study did not reveal any obvious kinetic abnormalities of red cell cation transport the presence of which in tissues involved in blood pressure regulation would favor the development or the maintenance of genetic hypertension in PHR.

Animals↗
PubMed1990

Reversibility and partial reactions of the Na(+)-K+ pump of rat erythrocytes.

An assay was developed to characterize the kinetic parameters of the Na(+)-K+ pump of rat erythrocytes under conditions as physiological as possible. Changes in the red cell Na+ and Rb+ content were determined in Na+ media (containing 2.5 mM inorganic phosphate (PO4) as a function of cell Na+ (2-8 mmol/l) and extracellular Rb+ (0.2-5 mM). Evaluation of the data revealed that under these conditions the Na(+)-K+ pump mediates, in addition to forward running 3 Nai+: 2 Rbo+ exchange, 1 Ki+:Rbo+ exchange and pump reversal (3 Nao+:2 Ki+ exchange). The two latter modes of Na(+)-K+ pump operation are accelerated by PO4 and lowering of cell Na+. At physiological cation and PO4 concentrations, 1Ki+:Rbo+ exchange contributes by 30-60% to total ouabain-sensitive Rb+ uptake. Thereby, the stoichiometry of ouabain-sensitive Na+ net-extrusion to Rb+ uptake is reduced to values between 1.0 and 0.5. Only at cell Na+ contents above 20 mmol/l the Na+:Rb+ stoichiometry approaches the value of 3:2 = 1.5. At certain constellations of Nai+ and Rbo+ the Na(+)-K+ pump cannot perform any net-transport of Na+ and K+ (Rb+). These equilibrium points are not far from those expected from thermodynamic considerations. The results demonstrate that in normal rat erythrocytes the reversible reaction cycle of the Na(+)-K+ pump runs in several modes of operation. The "abnormal" modes complicate the interpretation of unidirectional fluxes mediated by the Na(+)-K+ pump.

Animals↗
PubMed1990

Influence of chronic alterations of salt intake and aging on the kinetic of red cell Na+ and K+ transport in Sprague-Dawley rats.

The kinetics of Na+ and K+ (Rb)+ transport mediated by the Na(+)-K+ pump and Na(+)-K+ cotransport system (assessed as a function of Rb+o and Na+i) as well as the magnitude of cation leaks were determined in red cells of young male rats subjected to chronic salt deprivation or salt loading (0.1% and 8% NaCl diet). These salt intake alterations induced moderate kinetic changes of the Na(+)-K+ pump which did not result in significant changes of ouabain-sensitive (OS) Rb+ uptake or Na+ net extrusion at in vivo Na+i and K+o concentrations because a decreased affinity for Na+i in salt-loaded animals was compensated by an increased maximal transport rate. High furosemide-sensitive (FS) Rb+ uptake in red cells of salt-deprived rats was caused by an increase of both the maximal transport rate and the affinity for Rb+o. Cation leaks were also higher in salt-deprived than in salt-loaded rats. In three age groups of rats fed a 1% NaCl diet FS Rb+ uptake (but not FS Na+ net uptake) rose with age due to an increasing maximal transport rate whereas the affinity of the cotransport system for Rbo+ did not change. The age-dependent changes in the kinetics of the Na(+)-K+ pump resulted in a slight decrease of OS Rb+ uptake with age that was not paralleled by corresponding Na+ net extrusion. No major age-related changes of cation leaks were found. Thus some intrinsic properties of red cell transport systems can be altered by salt intake and aging.

Aging↗
PubMed1989

Distinction of two components of passive Ca2+ transport into human erythrocytes by Ca2+ entry blockers.

The nature of downhill Ca2+ net-transport into human erythrocytes was investigated using the experimental models of Ca2+ pump inhibition by vanadate and of intracellular chelation of Ca2+ by quin2. Ca2+ uptake by erythrocytes loaded with 0.5 mM vanadate and suspended in 145 mM Na+ -5 mM K+ media was reduced by about 60% when medium K+ was raised to 80 mM. Organic and inorganic Ca2+ entry blockers such as nifedipine (10(-5) M), verapamil (10(-4) M), diltiazem (10(-4) M), Co2+ (1.5 mM) and Cu2+ (0.1 mM) as well as the K+ channel blocker quinidine (1mM) inhibited Ca2+ uptake in 145 mM Na+ -5 mM K+ media by 60-75%. Flunarizine was less effective. In vanadate-loaded cells suspended in 70 mM Na+ -80 mM K+ media, in contrast, flunarizine exerted a dose-dependent inhibition of Ca2+ uptake by up to 80% at 10(-5) M, the other blockers being ineffective (except for verapamil at 10(-4) M). A similar pattern of inhibition was seen in quin2-loaded erythrocytes. The different susceptibility towards inhibitors may indicate that passive Ca2+ uptake by vanadate-loaded erythrocytes suspended in 145 mM Na+ -5 mM K+ media, on the one hand, and by vanadate-loaded erythrocytes suspended in 70 mM Na+ -80 mM K+ media as well as by quin2-loaded erythrocytes, on the other hand, is mediated by two different transport components.

Aminoquinolines↗
PubMed1987

Intracellular calcium content of human erythrocytes: relation to sodium transport systems.

To study the possible role of intracellular Ca (Cai) in controlling the activities of the Na+-K+ pump, the Na+-K+ cotransport and the Na+/Li+ exchange system of human erythrocytes, a method was developed to measure the amount of Ca embodied within the red cell. For complete removal of Ca associated with the outer aspect of the membrane, it proved to be essential to wash the cells in buffers containing less than 20 nM Ca. Ca was extracted by HClO4 in Teflon vessels boiled in acid to avoid Ca contaminations and quantitated by flameless atomic absorption. Cai of fresh human erythrocytes of apparently healthy donors ranged between 0.9 and 2.8 mumol/liter cells. The mean value found in females was significantly higher than in males. The interindividual different Ca contents remained constant over periods of more than one year. Sixty to 90% of Cai could be removed by incubation of the cells with A23187 and EGTA. The activities of the Na+-K+ pump, of Na+-K+ cotransport and Na+/Li+ exchange and the mean cellular hemoglobin content fell with rising Cai; the red cell Na+ and K+ contents rose with Cai. Ca depletion by A23187 plus EGTA as well as chelation of intracellular Ca2+ by quin-2 did not significantly enhance the transport rates. It is concluded that the large scatter of the values of Cai of normal human erythrocytes reported in the literature mainly results from a widely differing removal of Ca associated with the outer aspect of the membrane.

Antiporters↗
PubMed1979

Studies on lithium transport across the red cell membrane. V. On the nature of the Na+-dependent Li+ countertransport system of mammalian erythrocytes.

Ouabain-resistant Na+-Li+ countertransport was studied on erythrocytes of man, sheep, rabbit, and beef. A transport system, exchanging Li+ for Na+ in a ratio of 1:1, was present in all four species. Li+ uptake by the exchange system increased 30-fold in the order man less than HK-sheep less than LK-sheep less than rabbit less than LK-beef. This order is identical to that of ouabain-resistant Na+-Na+ exchange in these species, but bears no relation to the Na+-K+ pump activity. The activity of the Na+-Li+ exchange system varied up to 7 and 16-fold among individual red cell specimens from man and beef, the variability being much smaller in sheep and rabbit erythrocytes. The affinities of the system for Li+ and Na+ were similar among the species and individuals (half saturation of the external site at about 1 mM Li+ and 50 mM Na+, respectively). 50-60% of Na+-Li+ exchange was blocked by N-ethylmaleimide in all species. p-Chloromercuribenzene sulfonate inhibited the exchange only in beef and sheep erythrocytes (60-80%). The two SH-reagents act by decreasing the maximum activity of the system, whilst leaving its affinity for Li+ unaltered. Phloretin was a potent inhibitor in all species. 1 mM each of furosemide, ethacrynic acid, and quinidine induced only a slight inhibition. The Na+-Li+ exchange of human and beef erythrocytes increased 3.5-fold upon elevation of the extracellular pH from 6 to 8.5, the pH-dependence arising from a change in affinity of the system for the cations and being similar to that reported for ouabain-resistant Na+-Na+ exchange in beef erythrocytes. It is concluded that a transport system exists in the red cell membranes of the four species which can mediate ouabain-resistant exchange of either Na+ for Na+, Na+ for Li+, or Li+ for Li+. The exchange system exhibits essentially identical transport characteristics in the four species, but shows a marked inter- and intra-species variability in maximum transport capacity and some differences in susceptibility towards inhibitors. A similar transport system is probably present also in other tissues. The exchange system seems to be distinct from the conventional Na+-K+ pump and shows no clear relation to one of the furosemide-sensitive, ouabain-resistant Na+ transport systems described in the literature.

4-Chloromercuribenzenesulfonate↗
PubMed1979

Studies on lithium transport across the red cell membrane. VI. Properties of a sulfhydryl group involved in ouabain-resistant Na+-Li+ (and Na+-Na+) exchange in human and bovine erythrocytes.

The reactivity of the SH-group essential for ouabain-resistant Na+-Li+ (and Na+-Na+) exchange and its location within the membrane are studied on human and beef erythrocytes and beef red cell ghosts. N-ethylmaleimide (NEM), 1,6-hexane dimaleimide, and iodoacetamide can induce an irreversible, partial inhibition of Na+-Li+ exchange in erythrocytes of the two species. The development of the inhibition due to the alkylating agents is greatly accelerated by external Na+ and Li+. The inhibition takes 3 min (NEM) and 60 min (iodoacetamide) to come to completion in isotonic Na+ media, but is hardly detectable in choline+, K+ or Mg2+ media. The transport site of the exchange system and the site promoting NEM binding exhibit similar affinities for external Na+. The impermeable, monofunctional glutathione derivative of 1,6-hexane dimaleimide does not inhibit Na+-Li+ exchange. The mercurials PCMBS, PCMB, and Hg2+ inhibit Na+-Li+ exchange in beef, but not in human erythrocytes. The inhibitory action of PCMBS, being slightly accelerated by external Na+, is fully reversed by penetrating thiols such as 2-mercaptoethanol, whilst glutathione, an impermeable thiol, is ineffective. Pretreatment with PCMBS affords partial protection from the irreversible inhibition caused by NEM. Oxidation with copper orthophenanthroline inhibits Na+-Li+ exchange only when performed in the presence of penetrating thiols such as 2-mercaptoethanol. It is concluded that the SH-reagents studied inhibit Na+-Li+ exchange by modifying an essential SH-group of a membrane protein in such a way that the turnover number of the exchange system is reduced. This SH-group is separated from both the red cell exterior and interior by a penetration barrier and seems to be distinct from the cation binding site. The action of external Na+ and Li+ in promoting the reaction of alkylating inhibitors is interpreted to result from a conformational change of the transport protein induced by the binding of external Na+ or Li+.

4-Chloromercuribenzenesulfonate↗
PubMed1978

Evidence for anionic cation transport of lithium, sodium and potassium across the human erythrocyte membrane induced by divalent anions.

1. The passive net transport of Li+ and Na+ across the human red cell membrane was accelerated by the divalent anions carbonate, sulphite, oxalate, phosphite and malonate. Phthalate, maleate, sulphate and succinate were found additionally to stimulate downhill transport of K+. Marked differences in anion efficacy and selectivity were observed. 2. The effects of these 'carbonate type' anions were reversible and fully blocked by SITS, dipyridamole and other inhibitors of anion transfer. 3. Cation transport acceleration induced by the monovalent anions salicylate, benzoate, thiocyanate and 2,4-dinitrophenol were inhibited by dipyridamole, but not affected by SITS. A great number of mono- and polyvalent anions were without detectable influence on Li+ transport. 4. Li+ net uptake induced by oxalate exhibited a pH dependence similar to that reported for halide self exchange. 5. Transport acceleration by carbonate type anions displayed a linear, 1:1 dependence on the concentrations of both the anion and the cation and was symmetric with respect to the two sides of the membrane. 6. It is concluded that the divalent carbonate type anions form singly charged, negative 1:1 ion pairs with the respective alkali metal cations, the ion pairs traversing the red cell membrane via the anion exchange pathway. This concept of anionic formation of some of the ion pairs considered. The relative efficacies and cation selectivities of polyvalent anions can largely be explained on the basis of electrostatic interactions governing ion pair formation. However, the chelating properties, structural flexibility, polarizability of the anions and the accessibility of the ion pairs to the anion exchange pathway need also be considered. 7. An exchange of NaCO-3 ion pairs for internal HCO-3 or Cl- is discussed as a possible mode of cellular pH regulation.

Anions↗