Ca2+ permeability in deoxygenated sickle cells.

Deoxygenation of sickle cells is known to increase cation permeabilities (Na+, K+, and Ca2+). The possible mechanisms involved in the increased uptake of Ca2+ were investigated: activation of Ca2+ channels, involvement of the anion channel, and the formation of endocytic vacuoles. The Ca2+ channel blocker nifedipine reduced the deoxy-stimulated Ca2+ uptake by about 30% to 40%. The anion channel inhibitor DIDS (4,4' diisothiocyanate stilbene 2,2' disulfonate) inhibited the deoxy-stimulated Ca2+ uptake by approximately 50%. Maximal possible endocytic uptake, measured by using an impermeant marker ([3H] inuline), accounted for 6% to 9% of the total Ca2+ uptake. These data indicate that the deoxygenation-induced increase in Ca2+ permeability could result from both the activation of a Ca2+ channel and of a transport system for cations involving interactions between polymerized hemoglobin S, band 3 and other membrane components. Endocytosis appears to play only a minor role in the Ca2+ uptake of deoxygenated sickle cells.

Metabolism of phosphoinositides in sickle-cell anaemia erythrocytes - abstract

Polyphosphoinositides (PPI), minor components of red cell membrane phospholipids, undergo a rapid turnover of their phosphomonoester groups, but the role of the turnover has not been established definitely. It has been suggested that, in the red blood cell, phosphatidylinositol 4, 5-biphosphate (PIP2), and to a lesser extent, phosphatidylinositol 4-phosphate (PIP) are involved in the molecular interactions between skeletal and integral proteins and may play a part in cell shape and volume regulation. Since sickle-cell anaemia erythrocytes (SS cells) are known to have multiple structural and functional anomalies, particularly abnormal cell shape and volume regulation, we have investigated PPI metabolism in these cells. Concentrations of PPI and the 32P incorporation into these phospholipids have been measured in intact SS cells or isolated membranes, with AA cells as controls. The concentrations of phosphatidylinositol (PI) and PIP2 were the same in AA and SS cells. In contrast, major differences were found in the content of PIP which approximately doubled in SS cells. There was markedly higher incorporation of 32P in PPI of SS than AA cells after incubation with 32P (Pi). This increased turnover of PPI could be explained by a modification of the enzymes (kinases and phosphatases) involved in the metabolism of these phospholipids. The activities of the PI/PI 4-phosphate kinases have been studied in isolated membranes. The synthesis of PIP and PIP2 was increased in SS as compared to AA membranes. Further experiments are needed to elucidate the mechanism for this increased synthesis (AU)

Alteration in protein kinase C activity and subcellular distribution in sickle erythrocytes.

In agreement with previous data, membrane protein phosphorylation was found to be altered in intact sickle cells (SS) relative to intact normal erythrocytes (AA). Similar changes were observed in their isolated membranes. The involvement of protein kinase C (PKC) in this process was investigated. The membrane PKC content in SS cells, measured by [3H]phorbol ester binding, was about 6-times higher than in AA cells. In addition, the activity of the enzyme, measured by histone phosphorylation was also found to be increased in SS cell membranes but decreased in their cytosol compared to the activity in AA cell membranes and cytosol. The increase in membrane PKC activity was observed mostly in the light fraction of SS cells, fractionated by density gradient, whereas the decrease in cytosolic activity was only observed in the dense fraction. PKC activity, measured in cells from the blood of reticulocyte-rich patients, exhibited an increase in both membranes and cytosol, thus explaining some of the effects observed in the SS cell light fraction, which is enriched in reticulocytes. The increase in PKC activity in the membranes of SS cells is partly explained by their young age but the loss of PKC activity in their cytosol, particularly in that of the dense fraction, seems to be specific to SS erythrocytes. The relative decrease in membrane PKC activity between the dense and the light fractions of SS cells might be related to oxidative inactivation of the enzyme.

Calcium permeability in deoxygenated sickle erythrocytes - abstract

Sickle cell have an abnormally high level of calcium and, by an unknown mechanism, exhibit an increase in Caý+ permeability when they are sickled upon deoxygenation. This reversible increase in Caý+ permeability might contribute to cell dehydration by activation of K+ and water loss through the Caý+ permeability might contribute to cell dehydration by activation of K+ and water loss through the Caý+ dependent K+ channel (Gardos pathway). In the present study, the mechanism involved in Ca+ influx stimulation in sickle cells induced by deoxygenation was investigated by three different experiments: Ca2+uptake (1) in the presence of an extracellular impermeant marker to test endocytosis, (2) in the presence of the Caý+uptake (1) in the presence of an extracellular impermeant marker to test endocytosis, (2) in the presence of the Caý= -channel inhibitor Nifedipine, and (3) in the presence of an anion-exchanger inhibitor 4,4' - diisothiocyanatostilbene-2,2' - disulfonic acid (DIDS). These experiments revealed that endocytosis accounted for 6 percent to 19 percent of the Ca2+ uptake in deoxygenated sickle cells a nd that the increased Ca2+ influx was in part blocked by Nifedipine and by DIDS. The present findings, describing different pathways involved in the Caý+ increased permeability of deoxygenated sickle cells are of potential therapeutic interest (AU)

Endogenous calcium in sickle cells does not activate polyphosphoinositide phospholipase C.

Sickle-cell-anaemia erythrocytes (SS cells) are known to have a high Ca2+ content (particularly the dense cell fraction) and to take up Ca2+ on deoxygenation. It has been reported that this high Ca2+ was responsible for the activation of the Ca2+-dependent K+ loss, and of the Ca2+-sensitive polyphosphoinositide phospholipase C (PIC) in dense SS cells. We found that, either in the total population of SS cells or in the light or dense fractions, the content of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] was not changed, whereas that of phosphatidylinositol 4-phosphate was increased and that of phosphatidic acid (PtdOH) was decreased compared with normal (AA) erythrocytes. Deoxygenation-induced Ca2+ entry into SS cells did not change the concentration or, in 32P-prelabelled cells, the radioactivity of polyphosphoinositides and PtdOH. It also failed to induce the formation of inositol 1,4,5-trisphosphate, the product of PtdIns(4,5)P2 hydrolysis by PIC, which was measured by an original method using ion-pair reverse-phase h.p.l.c. Thus there was no evidence of an endogenous Ca2+ effect on the PIC activity in SS cells, in agreement with the demonstration that the excess Ca2+ in SS cells is compartmentalized into internal vesicles and unavailable as free Ca2+. The 32P incorporation in polyphosphoinositides and PtdOH was markedly higher in SS than in AA cells, but this increase was the same in both dense and light SS cells. The increase in the turnover of these phospholipids in SS cells is consistent either with an activation of the lipid kinases and phosphatases or with perturbation in the metabolic compartmentation of these lipids.

Hb J-Cordoba [alpha 2A beta 2(95)(FG2)Lys----Met]. A new Hb variant found in Argentina.

Hb J-Cordoba [alpha 2A beta 2(95)(FG2)Lys----Met], is one of the few hemoglobin variants discovered in Argentina. The structure and functional abnormalities are described. Hb J-Cordoba exhibits a slightly increased oxygen affinity, low cooperativity, and normal interaction with heterotropic cofactors.

Mouse alpha chains inhibit polymerization of hemoglobin induced by human beta S or beta S Antilles chains.

A murine model of sickle cell disease was tested by studying the polymerization of hybrid hemoglobin tetramers between alpha mouse and human beta S or beta S Antilles chains were prepared from Hb S Antilles, which was a new sickling hemoglobin inducing a sickle cell syndrome more severe than Hb S. The hybrid molecules did not polymerize in solution, indicating that the mouse alpha chains inhibited fiber formation. Consequently, a mouse model for sickle cell disease requires the transfer and expression of both alpha and beta S or beta S Antilles genes.

Ca2+ permeability and cytosolic Ca2+ concentration are not impaired in beta-thalassemic and hemoglobin C erythrocytes.

Total calcium content, determined by atomic absorption spectroscopy, Ca2+ influx, and cytosolic free Ca2+ concentration ( [Ca]i), estimated by a method involving the incorporation of a Ca2+ chelator (Quin 2), were measured in erythrocytes from beta-thalassemic (beta-thal) and hemoglobin C (CC) patients. Elevation of the total calcium content was observed in the cells from all patients, particularly in CC and splenectomized beta-thal. However, [Ca]i was within the normal range (approximately 25 nmol/L) in all the pathologic cells. Ca2+ influx in CC cells and in cells from nonsplenectomized beta-thal patients was also within the same range as that observed in control erythrocytes. In cells from splenectomized beta-thal patients, the kinetic of 45Ca influx was biphasic, indicating the existence of two pools of exchangeable Ca2+. Density fractionation of the cells from one splenectomized beta-thal patient showed that the rapid pool corresponded to the lightest cell fraction, which was also found to have the highest calcium content. The dense cells exhibited a normal Ca2+ influx as well as a smaller increase in total calcium content. It is suggested that, as in sickle cell anemia, the excess of Ca2+ in beta-thal cells is not free in the cytoplasm but trapped within endocytic vacuoles, especially in a population of abnormal cells that are normally removed by the spleen. In CC patients, who have a functional spleen, a different mechanism could be responsible for the calcium retention. In conclusion, the present results demonstrate that in these two cases of hemolytic anemia associated with high calcium content, Ca2+ permeability and the the level of cytosolic Ca2+ are normal.

Glycerated hemoglobin alpha 2 beta 2(82) (EF6) N-epsilon-glyceryllysine: a new post-translational modification occurring in erythrocyte bisphosphoglyceromutase deficiency.

A new minor Hb fraction initially designated Hbx, has been found in the hemolysate of a erythremic patient that we have previously described with a complete erythrocyte bisphosphoglyceromutase (BPGM) (E.C.2.7.5.4.) deficiency. Hbx (3.5% of the total) was detected by isoelectric focusing (IEF) and exhibited electrophoretic and chromatographic properties similar to that of several variants of the Hb central cavity. By density fractionation of red cells, it was demonstrated that Hbx was an aging hemoglobin as in the case of glycated Hb A1c. Functional studies revealed a low oxygen affinity and almost complete inhibition of the allosteric effect of the organic phosphate effectors. Structural studies demonstrated an absence of tryptic cleavage between the peptides beta T9 and beta T10 suggesting the presence of an adduct on Lys beta 82 or on a neighboring residue. FAB mass spectrometry, CID/MIKE spectra and a specific enzymatic assay with glyoxylate reductase, demonstrated that the 82 adduct was a glycerate moiety. It was concluded that Hbx was a glycerylated Hb: alpha 2 A beta 2(82) (EF6) N-epsilon-glyceryllysine, to our knowledge the first example of glycerylated protein. The mechanism of formation of glyceryl-Hb, which was found in the four studied subjects with a BPGM deficiency, remains to be determined.

Hemoglobin S Antilles: a variant with lower solubility than hemoglobin S and producing sickle cell disease in heterozygotes.

We have found a sickling variant, Hb S Antilles, alpha 2 beta 2(6 Glu----Val, 23 Val----Ile), that has the same electrophoretic mobility as Hb S but a distinct isoelectric focus and produces sickling in the carriers of the Hb A/S Antilles trait. The carriers' erythrocytes tend to sickle at O2 partial pressures similar to those that induce sickling in Hb S/C disease. Pure deoxy-Hb S Antilles is 50% as soluble as deoxy-Hb S (saturating concentration = 11 g X dl-1 compared to 18.4 for Hb S). Dilute solutions of pure Hb S Antilles have a lower oxygen affinity than those of Hb A or Hb S (partial pressure for 50% binding is 9 mm Hg compared to 5.5 mm Hg for Hb A or S at pH 7.00). A/S Antilles erythrocytes have a much lower oxygen affinity than A/S cells; this is further decreased in dense cells fractionated on a Percoll density gradient. Their oxygen equilibrium curves had anomalous shapes like those of S/S cells. Fiber formation in the erythrocytes of Hb S Antilles carriers is clearly due to its low solubility and oxygen affinity, showing that heterozygosity for this hemoglobin presents another sickle cell syndrome and suggesting that Hb S heterozygotes who exhibit symptoms of sickle cell disease should be carefully screened for double mutations.

Glycerated hemoglobin, alpha 2A beta 2(82) (EF6) N epsilon-glyceryllysine. A new post-translational modification occurring in erythrocyte bisphosphoglyceromutase deficiency.

A new minor Hb fraction initially designated Hbx, has been found in the hemolysate of an erythremic patient that we have previously described with a complete erythrocyte bisphosphoglycerate mutase (EC 5.4.2.4) deficiency. Hbx (3.5% of the total) was detected by isoelectric focusing and exhibited electrophoretic and chromatographic properties similar to those of several variants of the Hb central cavity. By density fractionation of red cells, it was demonstrated that Hbx was an aging hemoglobin as in the case of glycated Hb A1c. Functional studies revealed a low oxygen affinity and almost complete inhibition of the allosteric effect of the organic phosphate effectors. Structural studies demonstrated an absence of tryptic cleavage between the peptides beta T9 and beta T10 suggesting the presence of an adduct on Lys beta 82 or on a neighboring residue. Fast atom bombardment mass spectrometry and a specific enzymatic assay with glyoxylate reductase demonstrated that the beta 82 adduct was a glycerate moiety. It was concluded that Hbx was a glycerylated Hb, alpha 2A beta 2(82) (EF6) N epsilon-glyceryllysine, to our knowledge the first example of glycerylated protein. The mechanism of formation of glyceryl Hb, which was found in the four studied subjects with a bisphosphoglyceromutase deficiency, remains to be determined.

Hemoglobin J Iran alpha 2 beta 2 77 (EF1) his----Asp in a Russian-Armenian family.

A third case of Hb J Iran is reported. The propositus is of Russian-Armenian origin and was investigated for hematuria. The electrophoretic behavior and the characterization of primary structure are described. Hb J Iran is stable and has normal functional properties. High resolution Nuclear Magnetic Resonance spectra suggest the presence of structural perturbations in the heme pocket of the variant. Solubility studies of Hb S/Hb J Iran mixture indicated that His beta 77 belongs to a contact region of deoxy Hb S polymers.

Interaction of hemoglobin Siriraj with hemoglobin S: a mild sickle cell syndrome.

Hb Siriraj is a beta chain variant in which beta 7 (A4) Glu is replaced by a lysine. It has been encountered in association with Hb S in a black man from Martinique. Some properties of Hb Siriraj are compared, particularly, with Hb C [alpha 2 beta 26(A3)Glu----Lys], and a study of its in vitro interaction with Hb S is discussed.

Compartmentalization of Ca2+ in sickle cells.

Control (AA) and sickle cell anemia (SS) erythrocytes were loaded with Ca-chelator (Quin2 or Benz2) to increase the cellular exchangeable Ca2+ pool and to measure the Ca2+ exchange fluxes and the cytosolic ionized Ca2+ ([Ca]i) (Lew et al., 1982, Nature, 298, 478). The chelator incorporation induced a decrease in the ATP content which was smaller in SS than in AA cells and partially reversible upon reincubation in a chelator-free medium. The amount of trapped chelator was determined by two methods: 45Ca binding to the chelator in Ca-ionophore treated cells in Ca-EGTA buffers and [3H]Quin2 incorporation. A slight over-estimation of the chelator content was found with the second method but incorporation was the same in both types of cells. The kinetics of 45Ca equilibration and 45Ca release were used to measure Ca2+ fluxes and [Ca]i in oxygenated chelator-loaded cells. SS cells, as compared to AA cells, exhibited a moderate increase in Ca2+ fluxes (30-75%) but [Ca]i remained in the same range (about 20 nM). Thus the excess of Ca2+ found in SS cells is not available for the Ca2+ pump or the K+ channel a conclusion in agreement with that of Bookchin et al. (1984, Cell Calcium, 5, 277). Analysis of the 45Ca kinetics showed that in AA cells, exchangeable Ca2+ behaved as one compartment. In SS cells, the existence of a second slowly-exchangeable Ca2+ compartment was demonstrated. This latter (3-5 mumol/l cells) was independent of the concentration of the chelator and thus could represent exchangeable Ca2+ enclosed within the intracellular inside-out vesicles recently observed in SS cells (Williamson et al., 1984, J. Cell. Biol., 99, 430a). Alternatively, these two kinetic pools could reflect heterogeneity of the SS cell population.

Kinetics of polymerization of hemoglobin S modified by thiol reagents and by oxidation.

The effects of four thiol reagents on the kinetics of polymerization of hemoglobin S have been studied in high phosphate buffer (1.8 M), in the presence (3 mM) or absence of sodium dithionite, depending on the reduction of mixed disulfides of Hb in the presence of this reducing agent. The effect of oxidized forms (methemoglobin) of HbS on the kinetics of aggregation of deoxyHbS was also studied because of the presence of 33% metHbS when HbS was modified by 4-aminophenyl disulfide. In the presence of sodium dithionite, the delay times prior to polymerization of deoxyHbS modified by N-ethylmaleimide, iodoacetamide and 4-aminophenyl disulfide were, respectively, 1.5-, 1.35- and 1.15-times longer than that of native deoxyHbS. The results indicate that the radicals bound to the cysteine beta 93 residue inhibit the contacts in the polymer formation to various extents but do not modify the size of the nuclei.

Determination of the dissociation constant of oligomeric proteins by size-exclusion high-performance liquid chromatography: application to human haemoglobin.

The measurement of protein retention volumes on a size-exclusion chromatographic column offers the possibility of determining dissociation constants for oligomeric proteins, as changes in the retention volume, depending on the concentration of the protein, are due to a dissociation equilibrium. The retention volume may be calibrated in terms of dissociation constant by using either extreme concentration conditions or chemical modifications that shift the equilibrium towards a single species. When zonal chromatography is used, the dilution during elution modifies the equilibrium state. In contrast, the saturation method permits the concentrations of the different species to be kept constant. These two methods were compared and the elution factor that must be used in zonal chromatography on high-performance size-exclusion columns (LiChrospher Diol) was obtained. The tetramer-dimer dissociation constants of normal and modified haemoglobins were measured by this method, and the results are in accordance with flash photolysis measurements.

[Abnormal hemoglobins identified in Martinique]. / Hémoglobines anormales identifiées à la Martinique.

Epidemiologic programs in Martinique during the last 10 years and particularly the last 5, have allowed the determination of the Hb S, Hb C, beta thalassemia traits frequencies. A number of rare variants have been detected during the course of these screening programs. Many of these Hb variants have been analysed at the structural level. For some of them a pathologic interaction with Hb S is observed (Hb D Punjab, Hb O Arab...), and the use of electrophoretic mobilities obtained with the reference samples provides the basis of a rapid, highly probable presumptive identification and then, a useful tool, when for example genetic counselling is necessary.

Effects of the alpha 20 mutation on the polymerization of Hb S.

The contribution of the alpha 20 residues in intermolecular contacts present in hemoglobin S fibers was investigated with mixtures of Hb Le Lamentin alpha 2(20)His----Gln beta 2A and of hemoglobin S alpha 2A beta 2(6)Glu----Val and with artificial hybrids alpha 2(20)His----Gln beta 2(6)Glu----Val. This study showed an increased solubility and delay time of polymerization of Hb S in solution only when the mutation at the alpha 20 residue is cis to the beta 6 Val contact. No modification of the polymerization process occurs when the mutation is trans to this beta 6 Val contact. This result is in agreement with the crystal model of Wishner and Love, who showed that one of the two alpha 20 residues of the Hb S tetramer was involved in an axial contact between hemoglobin S molecules in the crystals of Hb S ( Wishner , B.C., Ward, K.B., Lattman , E.E. and Love, W.E. (1975) J. Mol. Biol. 98, 179-194). The present observation is a new illustration of the validity of the crystal model for the structure of the fibers based on pairs of double filaments.

Sickle cell hemoglobin fiber formation strongly inhibited by the Stanleyville II mutation (alpha 78 Asn leads to Lys).

A double mutant hemoglobin possessing both the Hb S (beta 6 Glu leads to Val) and the Hb Stanleyville II (alpha 78 Asn leads to Lys) mutations has been purified from the blood of a donor heterozygous for both of the mutations. The purification required two chromatography steps, with the second permitting resolution of the double mutant from Hb A2 remaining after the first step. Measurement of the competence for fiber formation by the double mutant hemoglobin was carried out by the centrifugation of gels to obtain Csat. The double mutant was found to have a greatly elevated Csat, 26.4 gm/dl, compared to 15.2 gm/dl for the Hb S control. The concentration of the pellet of the centrifuged gel for the double mutant was in the range 48-50 gm/dl, suggesting that no major rearrangement in the structure of the fibers had been induced by the Stanleyville II mutation. Electron microscopic observations on the fibers of the double mutant confirmed that a normal appearance was maintained.

A new silent hemoglobin variant in a black family from French West Indies, hemoglobin Le Lamentin alpha 20 His replaced by Gln.

A new abnormal hemoglobin Hb Le Lamentin alpha 20 (B1) His replaced by Gln was discovered during a survey of cord blood from the French West Indies (Martinique). This variant displays an electrophoretic pattern similar to that of Hb A but can be isolated by isoelectric focusing (IEF) and Biorex 70 chromatography. Family studies showed the presence of this hemoglobin variant in the father and in two of his three children. Hematological data from the carriers were normal.