Effect of cetiedil, an in vitro antisickling agent, on erythrocyte membrane cation permeability

Pharmacology of Small- and Intermediate-Conductance Calcium-Activated Potassium Channels

The three small-conductance calcium-activated potassium (K_Ca2) channels and the related intermediate-conductance K_Ca3.1 channel are voltage-independent K⁺ channels that mediate calcium-induced membrane hyperpolarization. When intracellular calcium increases in the channel vicinity, it calcifies the flexible N lobe of the channel-bound calmodulin, which then swings over to the S4-S5 linker and opens the channel. K_Ca2 and K_Ca3.1 channels are highly druggable and offer multiple binding sites for venom peptides and small-molecule blockers as well as for positive- and negative-gating modulators. In this review, we briefly summarize the physiological role of K_Ca channels and then discuss the pharmacophores and the mechanism of action of the most commonly used peptidic and small-molecule K_Ca2 and K_Ca3.1 modulators. Finally, we describe the progress that has been made in advancing K_Ca3.1 blockers and K_Ca2.2 negative- and positive-gating modulators toward the clinic for neurological and cardiovascular diseases and discuss the remaining challenges.

Sickle cell dehydration: Pathophysiology and therapeutic applications

Cell dehydration is a distinguishing characteristic of sickle cell disease and an important contributor to disease pathophysiology. Due to the unique dependence of Hb S polymerization on cellular Hb S concentration, cell dehydration promotes polymerization and sickling. In double heterozygosis for Hb S and C (SC disease) dehydration is the determining factor in disease pathophysiology. Three major ion transport pathways are involved in sickle cell dehydration: the K-Cl cotransport (KCC), the Gardos channel (KCNN4) and Psickle, the polymerization induced membrane permeability, most likely mediated by the mechano-sensitive ion channel PIEZO1. Each of these pathways exhibit unique characteristics in regulation by oxygen tension, intracellular and extracellular environment, and functional expression in reticulocytes and mature red cells. The unique dependence of K-Cl cotransport on intracellular Mg and the abnormal reduction of erythrocyte Mg content in SS and SC cells had led to clinical studies assessing the effect of oral Mg supplementation. Inhibition of Gardos channel by clotrimazole and senicapoc has led to Phase 1,2,3 trials in patients with sickle cell disease. While none of these studies has resulted in the approval of a novel therapy for SS disease, they have highlighted the key role played by these pathways in disease pathophysiology.

Expression and Role of the Intermediate-Conductance Calcium-Activated Potassium Channel KCa3.1 in Glioblastoma

Glioblastomas are characterized by altered expression of several ion channels that have important consequences in cell functions associated with their aggressiveness, such as cell survival, proliferation, and migration. Data on the altered expression and function of the intermediate-conductance calcium-activated K (KCa3.1) channels in glioblastoma cells have only recently become available. This paper aims to (i) illustrate the main structural, biophysical, pharmacological, and modulatory properties of the KCa3.1 channel, (ii) provide a detailed account of data on the expression of this channel in glioblastoma cells, as compared to normal brain tissue, and (iii) critically discuss its major functional roles. Available data suggest that KCa3.1 channels (i) are highly expressed in glioblastoma cells but only scantly in the normal brain parenchima, (ii) play an important role in the control of glioblastoma cell migration. Altogether, these data suggest KCa3.1 channels as potential candidates for a targeted therapy against this tumor.

Ion transport pathology in the mechanism of sickle cell dehydration

Polymers of deoxyhemoglobin S deform sickle cell anemia red blood cells into sickle shapes, leading to the formation of dense, dehydrated red blood cells with a markedly shortened life-span. Nearly four decades of intense research in many laboratories has led to a mechanistic understanding of the complex events leading from sickling-induced permeabilization of the red cell membrane to small cations, to the generation of the heterogeneity of age and hydration condition of circulating sickle cells. This review follows chronologically the major experimental findings and the evolution of guiding ideas for research in this field. Predictions derived from mathematical models of red cell and reticulocyte homeostasis led to the formulation of an alternative to prevailing gradualist views: a multitrack dehydration model based on interactive influences between the red cell anion exchanger and two K(+) transporters, the Gardos channel (hSK4, hIK1) and the K-Cl cotransporter (KCC), with differential effects dependent on red cell age and variability of KCC expression among reticulocytes. The experimental tests of the model predictions and the amply supportive results are discussed. The review concludes with a brief survey of the therapeutic strategies aimed at preventing sickle cell dehydration and with an analysis of the main open questions in the field.

Inhibition of the antigen-induced activation of RBL-2H3 cells by charybdotoxin and cetiedil

Quinidine and Ba(2+), non-selective K(+)-channel blockers, have previously been shown to inhibit antigen-induced mediator (beta-hexosaminidase) release from RBL-2H3 cells, a mucosal-type mast cell line. We therefore used selective blockers of Ca(2+)-activated and other K(+) channels to determine if there was a role for these channels in antigen-induced mediator release. Charybdotoxin and cetiedil dose-dependently inhibited beta-hexosaminidase release with IC(50) values of 133 nM and 84 microM, respectively. Charybdotoxin also inhibited the repolarization phase of the antigen-induced biphasic change in the membrane potential (IC(50) 84 nM), antigen-stimulated 86Rb(+)-efflux and increase in free intracellular calcium, [Ca(2+)](i). Iberiotoxin, margatoxin, apamin and tetraethylammonium had no effect on beta-hexosaminidase release. These results suggest that K(+) conductances play a significant role in mediator release from RBL-2H3, that these conductances are of the intermediate conductance Ca(2+)-activated K(+) channel (IK(Ca)) type, and that they are somewhat similar to those which have been described in red blood cells, though they are much less sensitive to clotrimazole.

Pharmacology of the human red cell voltage-dependent cation channel

The activation and pharmacological modulation of the nonselective voltage-dependent cation (NSVDC) channel from human erythrocytes were studied. Basic channel activation was achieved by suspending red cells in a low Cl(-) Ringer (2 mM), where a positive membrane potential (V(m) = E(Cl)) immediately developed. Voltage- and time-dependent activation of the NSVDC channel occurred, reaching a cation conductance (g+) of 1.5-2.0 microS cm(-2). In the presence of the classical Gárdos channel blocker clotrimazole (0-50 microM), activation occurred faster, and g+ saturated dose-dependently (EC50 = 14 microM) at a value of about 4 microS cm(-2). The clotrimazole analogues TRAM-34, econazole, and miconazole also stimulated the channel, whereas the chemically more distant Gárdos channel inhibitors nitrendipine and cetiedil had no effects. Although the potency for modulation of the NSVDC channel is much lower than the IC50 value for Gárdos channel inhibition, clotrimazole (and its analogues) constitutes the first chemical class of positive modulators of the NSVDC channel. This may be an important pharmacological "fingerprint" in the identification of the cloned equivalent of the erythrocyte channel.

The paradox of hemoglobin SC disease

Homozygous HbC gene results only in mild hemolytic anemia. In HbSC disease red cells contain equal levels of HbS and HbC. It is a paradox that HbSC exhibit a moderately severe phenotype in spite of being a mixture of HbS trait and HbC trait, neither of which has significant pathology. Why does the combination of these two Hbs result in a serious disease? The short answer is that HbC enhances, by dehydrating the SC red cell, the pathogenic properties of HbS, resulting in a clinically significant disorder, but somewhat milder that sickle cell anemia (SCA). Nevertheless, retinnitis proliferans, osteonecrosis, and acute chest syndrome have equal or higher incidence in HbSC disease compared to SCA. This pathogenic trick is accomplished by HbC inducing, by mechanisms not fully understood, an increase in the activity of K:Cl cotransport that induces the lost of K(+) and consequently of intracellular water. This event creates a sufficient increase of MCHC, so that the lower levels of HbS found in SC red cells can polymerize rapidly and effectively. This situation offers a unique opportunity: if we could inhibit the effect of HbC on K(+) transport we can cure the disease.

Erythrocyte-active agents and treatment of sickle cell disease

The sickle hemoglobin (HbS)-containing erythrocyte and its membrane represent a logical target for sickle cell disease therapy. Several antisickling agents which interfere with HbS polymerization have been studied over the last 30 years, but none has overcome the challenge of delivering high concentrations inside the sickle red blood cell without toxicity. The sickle erythrocyte membrane has also been targeted for therapeutic developments. Prevention of sickle cell dehydration by use of specific blockers of ion transport pathways mediating potassium loss from the sickle erythrocyte has been shown to be a feasible strategy in vitro, in vivo in transgenic sickle mice, and in patients. Other approaches have focused on improving the hemorheology of sickle erythrocytes and reducing their abnormal adhesion to endothelial cells. These potential treatments could be used alone or in combination with other approved therapies, such as hydroxyurea.

Volume control in sickle cells is facilitated by the novel anion conductance inhibitor NS1652

A low cation conductance and a high anion conductance are characteristic of normal erythrocytes. In sickle cell anemia, the polymerization of hemoglobin S (HbS) under conditions of low oxygen tension is preceded by an increase in cation conductance. This increase in conductance is mediated in part through Ca++-activated K+ channels. A net efflux of potassium chloride (KCl) leads to a decrease in intracellular volume, which in turn increases the rate of HbS polymerization. Treatments minimizing the passive transport of ions and solvent to prevent such volume depletion might include inhibitors targeting either the Ca++-activated K+ channel or the anion conductance. NS1652 is an anion conductance inhibitor that has recently been developed. In vitro application of this compound lowers the net KCl loss from deoxygenated sickle cells from about 12 mmol/L cells/h to about 4 mmol/L cells/h, a value similar to that observed in oxygenated cells. Experiments performed in mice demonstrate that NS1652 is well tolerated and decreases red cell anion conductance in vivo.

N-ethylmaliemide (NEM)-stimulated potassium transport in camel erythrocytes

In this study N-ethylmaliemide (NME)-stimulated, ouabain-resistant potassium influx in camel erythrocytes was measured using the radioactive rubidium tracer 86Rb+. The results showed that camel erythrocytes responded to NEM pretreatment by a threefold increase in influx which was Cl- dependent. The anion dependence of K+ influx in pre-treated cells was Br- > Cl- > NO3-. The pH dependence curve for NEM-stimulated K+ influx and the combination between volume and NEM stimulation in camel erythrocytes were determined. The findings indicated that the camel erythrocytes potassium transport system has many similarities to that of other mammalian species.

Review: sickle cell disease: present and future treatment

Over the past few decades, the life expectancy of patients with sickle cell disease has improved. This has been because of better supportive care and greater awareness of the complications of this disorder. Recent successes of neonatal screening, childhood prophylactic penicillin, and, perhaps, hydroxyurea in adults may further extend the life of sickle cell disease patients. This review will do the following: 1) briefly highlight the major aspects of the conventional treatment of sickle cell disease, 2) address the present use of hydroxyurea in more depth, and 3) succinctly preview what the near-term future of treatment may bring.

The synthesis and some pharmacological actions of the enantiomers of the K(+)-channel blocker cetiedil

Cetiedil ((+/-)-2-cyclohexyl-2-(3-thienyl)ethanoic acid 2-(hexahydro-1 H-azepin-1-yl) ethyl ester) possesses anti-sickling and analgesic, antispasmodic, local anaesthetic and vasodilator activities. A total synthesis and circular dichroism spectra of the enantiomers of cetiedil is described, together with a comparison of their effectiveness as blockers of the Ca(2+)-activated K+ permeability of rabbit erythrocytes; the contractile response of intestinal smooth muscle to acetylcholine; the Ca(2+)-dependent contraction of depolarized intestinal muscle; and the cell volume-sensitive K+ permeability (Kvol) of liver cells. The enantiomers did not differ substantially in their ability to block the Ca(2+)-activated K+ permeability of rabbit red cells or in their effectiveness as blockers of the contractile response of depolarized smooth muscle to externally applied Ca2+. There was a clear difference in the muscarinic blocking activity of the enantiomers, as assessed by inhibition of the contractile response of intestinal smooth muscle to acetylcholine; (+)-cetiedil was 7.7 +/- 0.2 (s.d.) times more active than the (-) from. The enantiomers also differed in their potency as blockers of the increase in membrane conductance which occurs when liver cells swell. The concentration of (+)-cetiedil needed to reduce the conductance increase by 50% was 2.04 +/- 0.54 (s.d.) microM; (-)-cetiedil was 2.6 +/- 0.8 (s.d.) times less active (IC50 of 5.2 +/- 1.2 microM). Differences in the biological actions of the enantiomers of cetiedil indicate that a more extensive study could be rewarding in relation to the use of the enantiomers both in therapeutics and in the study of K+ channels.

Therapy with oral clotrimazole induces inhibition of the Gardos channel and reduction of erythrocyte dehydration in patients with sickle cell disease

Pathologic water loss from sickle erythrocytes concentrates the abnormal hemoglobin and promotes sickling. The Ca2+-activated K+ channel (Gardos channel) contributes to this deleterious dehydration in vitro, and blockade of K+ and water loss via this channel could be a potential therapy in vivo. We treated five subjects who have sickle cell anemia with oral clotrimazole, a specific Gardos channel inhibitor. Patients were started on a dose of 10 mg clotrimazole/kg/d for one week. Protocol design allowed the daily dose to be escalated by 10 mg/kg each week until significant changes in erythrocyte density and K+ transport were achieved. Blood was sampled three times a week for hematological and chemical assays, erythrocyte density, cation content, and K+ transport. At dosages of 20 mg clotrimazole/kg/d, all subjects showed Gardos channel inhibition, reduced erythrocyte dehydration, increased cell K+ content, and somewhat increased hemoglobin levels. Adverse effects were limited to mild/moderate dysuria in all subjects, and a reversible increase in plasma alanine transaminase and aspartic transaminase levels in two subjects treated with 30 mg clotrimazole/kg/d. This is the first in vivo evidence that the Gardos channel causes dehydration of sickle erythrocytes, and that its pharmacologic inhibition provides a realistic antisickling strategy.

Volume-dependent potassium transport in camel red blood cells

In this study the volume-dependent, ouabain-resistant K+ influx and efflux in camel red blood cells were measured with the tracer 86Rb+. The results showed that the camel erythrocytes do not have the Na(+)-K+ cotransport. The cell swelling increases a ouabain-resistant K+ influx and shrinkage decreases it nearly two-fold. The swelling-stimulated K+ influx and efflux were chloride dependent. The anion dependence of K+ influx in swollen cells was as follows: Br- > Cl- > NO3. The pH-dependent curve for swelling-stimulated potassium influx, and the active K+ influx in camel erythrocytes were determined. The findings indicate that camel erythrocytes' potassium transport system has many similarities to other mammalian species.

Cation transport and volume regulation in sickle red blood cells

Cellular dehydration is one of several pathological features of the sickle cell. Cation depletion is quite severe in certain populations of sickle cells and contributes to the rheological dysfunction that is the root cause of vascular occlusion in this disease. The mechanism of dehydration of sickle cells in vivo has not been ascertained, but three transport pathways may play important roles in this process. These include the deoxygenation-induced pathway that permits passive K+ loss and entry of Na+ and Ca2+; the K(+)-Cl- cotransport pathway, activated by acidification or cell swelling; and the Ca(2+)-activated K+ channel, or Gardos pathway, presumably activated by deoxygenation-induced Ca2+ influx. Recent evidence suggests that these pathways may interact in vivo. Heterogeneity exists among sickle cells as to the rate at which they become dense, suggesting that other factors may affect the activity or interactions of these pathways. Understanding the mechanism of dehydration of sickle cells may provide opportunities for pharmacological manipulation of cell volume to mitigate some of the symptoms of sickle cell disease.

Physiologic and rheologic effects of the antisickling agent ethacrynic acid and its N-butylated derivative on normal and sickle erythrocytes

Ethacrynic acid, a loop diuretic, has been shown to inhibit hemoglobin S polymerization. Until now, however, most studies were performed using purified solutions of hemoglobin S. The experiments reported here were designed to examine the effects of ethacrynic acid and its n-butryic acid derivative on the rheological and physiological properties of intact red blood cells. Using net and unidirectional flux measurements, both agents were shown to cause ion and water loss from normal and sickle erythrocytes. Since cell shrinkage adversely influences red cell rheology, it is unlikely that this class of compounds, despite its ability to inhibit hemoglobin S polymerization, will prove useful in the treatment of sickle cell disease.

Volume-dependent K+ transport in rabbit red blood cells comparison with oxygenated human SS cells

In this study the volume-dependent or N-ethylmaleimide (NEM)-stimulated, ouabain-insensitive K+ influx and efflux were measured with the tracer 86Rb+ in rabbit red blood cells. The purpose of the work was to examine the rabbit as a potential model for cell volume regulation in human SS red blood cells and also to investigate the relationship between the NEM-reactive sulfhydryl group(s) and the signal by which cell swelling activates the transport. Ouabain-resistant K+ efflux and influx increase nearly threefold in cells swollen hypotonically by 15%. Pretreatment with 2 mM NEM stimulates efflux 5-fold and influx 10-fold (each measured in an isotonic medium). The ouabain-resistant K+ efflux was dependent on the major anion in the medium. The anion dependence of K+ efflux in swollen or NEM-stimulated cells was as follows: Br- greater than Cl- much greater than NO3- = acetate. The magnitudes of both the swelling- and the NEM-stimulated fluxes are much higher in young cells (density separated but excluding reticulocytes) than in older cells. Swelling- or NEM-stimulated K+ efflux in rabbit red blood cells was inhibited 50% by 1 mM furosemide, and the inhibitory potency of furosemide was enhanced by extracellular K+, as is known to be true for human AA and low-K+ sheep red blood cells. The swelling-stimulated flux in both rabbit and human SS cells has a pH optimum at approximately 7.4. We conclude that rabbit red blood cells are a good model for swelling-stimulated K+ transport in human SS cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxpentifylline and cetiedil citrate improve deformability of dehydrated sickle cells

Erythrocytes from 14 patients with homozygous sickle cell anaemia were treated with the calcium ionophore A23187 to induce loss of cellular potassium and water. The dehydrated cells showed a decrease in filterability (loss of deformability) through pores of 5 micron diameter. Oxpentifylline and cetiedil citrate, which preserve erythrocyte cation and water content, had a significant (p less than 0.01) protective effect against loss of deformability at a concentration of 1 mumol/l. Oxpentifylline showed no adverse effect on the rheology, morphology, or haemolysis of sickle cells at concentrations up to 500 mumol/l. Drugs that act on the erythrocyte membrane to maintain cell hydration are of potential rheological benefit in sickle cell anaemia.

Cetiedil, a drug that inhibits acetylcholine release in Torpedo electric organ

The effects of cetiedil, a vasodilatator substance with reported anticholinergic properties, were examined on cholinergic presynaptic functions at the nerve electroplaque junction of Torpedo marmorata using either synaptosomes or slices of intact tissue. Cetiedil abolished the calcium-dependent release of acetylcholine (ACh) triggered by depolarization or by addition of A23187 ionophore, a finding localizing the site of action downstream from the calcium entry step. In addition, a direct effect on the release process itself was indicated by the observation that cetiedil blocks the release of ACh mediated by a recently isolated presynaptic membrane protein, the mediatophore, reconstituted into ACh-containing proteoliposomes. In all three preparations, ACh release was inhibited by cetiedil with a Ki of 5-8 microM. Under the conditions used in these release experiments, the synthesis of ACh and its compartmentation within the nerve terminals were not modified. However, the drug was able to reduce high-affinity choline uptake and vesicular ACh incorporation when it was given together with the radioactive precursor, a result showing that cetiedil has a broad inhibitory action on cholinergic uptake processes.

Effect of N-ethylmaleimide on K transport in density-separated human red blood cells

N-ethylmaleimide (NEM) is a sulfhydryl-reacting agent known to stimulate chloride-dependent K transport in a variety of red cells. In high K sheep red cells, NEM-induced K movements are greater in magnitude in young cells compared with old cells. We hypothesized that human red cells might respond to NEM like high K sheep red cells. To test this idea, cells of various age were exposed to 0.5 mM NEM. We found that, after a 4-h incubation, young cells lost 50% of cell K, compared with 10% K loss in older cells. K loss in all fractions was inhibited by chloride replacement or furosemide.

Cell volume regulation in hemoglobin CC and AA erythrocytes

Swelling hemoglobin CC erythrocytes stimulates a ouabain-insensitive K flux that restores original cell volume. This volume regulatory pathway was characterized for its anion dependence, sensitivity to loop diuretics, and requirement for Na. The swelling-induced K flux was eliminated if intracellular chloride was replaced by nitrate and both swelling-activated K influx and efflux were partially inhibited by 1 mM furosemide or bumetanide. K influx in swollen hemoglobin CC cells was not diminished when Na in the incubation medium was replaced with choline, indicating Na independence of the swelling-induced flux. Identical experiments with hemoglobin AA cells also demonstrated a swelling-induced increase in K flux, but the magnitude and duration of this increase were considerably less than that seen with hemoglobin CC cells. The increased K flux in hemoglobin AA cells was likewise sensitive to anion replacement and to loop diuretics and did not require the presence of Na. These data indicate that a volume-activated K pathway with similar transport characteristics exists in both hemoglobin CC and AA red cells.

Regulation of erythrocyte cation and water content in sickle cell anemia

The pathophysiological events in sickle cell disease are critically dependent on the intracellular concentration of hemoglobin S, which varies inversely with cell cation and water content. Erythrocytes of SS homozygotes exposed to oxygen or carbon monoxide decrease their potassium and water content through a pathway for potassium transport that is activated by both cell swelling and decrease in internal pH. This pathway is not inhibited by ouabain either with or without bumetanide. When SS erythrocytes were separated according to density, the pH- and volume-dependent potassium transport was greatest in the least dense fraction and was reduced in the densest cells. This pathway, which does not depend on polymerization of sickle hemoglobin, may be important in regulating the cation and water content of SS erythrocytes.

Passive sodium and potassium movements in sickle erythrocytes

Deoxygenation causes an increase in passive Na and K movements across the membrane of the sickle erythrocyte. Some investigators find that these ion movements are accompanied by cell dehydration, while others find no evidence for cell water loss with sickling. Because gelation of hemoglobin S would be enhanced by cell water loss, we reinvestigated Na and K movements in sickle cells to define further the role that ion movements might play in the pathogenesis of sickling. With deoxygenation, we found that sickle cells gained Na and lost K without losing cell water. These net ion movements were not seen in control red blood cells. For sickle cells, deoxygenation also increased passive unidirectional influxes of Na and K, effects not observed when control red blood cells were deoxygenated. The deoxygenation-induced passive influxes of Na and K in sickle cells were not diminished by anion substitution or by the addition of the diuretic furosemide. We also found differences in passive Na and K fluxes between oxygenated sickle cells and normal red blood cells. The addition of furosemide or replacement of Cl with NO3 or SCN, maneuvers that largely reduced passive Na and K movements in oxygenated normal cells, had no effect on Na and K movements in oxygenated sickle cells. These findings militate against the idea that solute and water loss occur as a consequence of deoxygenation but do indicate that there are acquired membrane abnormalities in sickle red blood cells.

Effects of cetiedil on the oxidative metabolism of activated polymorphonuclear leucocytes

Cetiedil, alpha-cyclohexyl-3-thiopheneacetic acid 2-(hexahydro-lH-azepin-l-yl)-ethyl ester, was found to specifically suppress oxygen uptake by polymorphonuclear leucocytes (PMN) that were exposed to myristate or heat-killed E. coli. The chemical had no effect on the basal respiration rate of PMN in the resting state. Inhibition of oxygen uptake by cetiedil was proportionate to the degree of inhibition of the generation of O-2 and H2O2. It was also found that cetiedil suppressed the rate of the phagocytosis by PMN of opsonized oil droplets. Cetiedil had no effect on subcellular NADPH oxidase, an enzyme responsible for the respiratory burst that is activated by the perturbation of PMN plasma membrane with phagocytable particles or stimulators such as myristate. These results suggest that cetiedil affects the trigger mechanism of the plasma membrane to inhibit the activation of NADPH oxidase.

Compartmentalization of sickle-cell calcium in endocytic inside-out vesicles

Much recent interest in the mechanism of dehydration of the dense subpopulation of sickle-cell anaemia (SS) red cells, including the 'irreversibly sickled cells' (ISCs), stems from the view that these relatively rigid cells have a major role in the two main clinical features of the disease, namely haemolytic anaemia and microvascular occlusion. The discovery that SS red cells have an elevated calcium content and accumulate Ca2+ during deoxygenation-induced sickling suggested a working hypothesis of wide appeal for the mechanism of cell dehydration: retained calcium would activate the red cell Ca2+-sensitive K+ channels, causing progressive net loss of KCl and water. However, retained calcium, which seemed as weakly bound to cytoplasmic buffers as in normal red cells, failed to show any measurable activation of K+ channels or Ca2+ pumps in metabolically normal SS cells, despite the apparent functional normality or near-normality of these transport systems. We now offer a possible explanation for this failure. We show that, contrary to the traditional views, SS cells, and to a lesser extent normal human red cells, possess intracellular vesicles with ATP-dependent Ca2+-accumulating capacity, and that nearly all the measurable calcium of fresh SS cells is contained within such vesicles, probably in the form of precipitates with inorganic or organic phosphates.

Membrane expansion as a mechanism explaining the antisickling action of ticlopidine observed in vitro

Ticlopidine, a platelet antiaggregant, has shown some efficacity in a clinical trial in patients with sickle cell disease. We have studied this agent in vitro to evaluate its effects on sickle erythrocyte. Ticlopidine effects sickling in vitro not by direct interaction with hemoglobin, but via strong binding to the red cell membrane. The density of the whole cell population is decreased when cells are treated with 0.1 mM ticlopidine, which is higher than the concentrations of 1 microM potentially achievable in vivo. Since hemoglobin concentration influences the delay time for gelling, its decrease in the red cell could have a beneficial effect. Such a partial inhibition of the polymerization is shown by oxygen equilibrium studies at various ionic strengths.

Effect of cetiedil on platelet aggregation and thromboxane synthesis

Cetiedil was found to inhibit platelet aggregation and thromboxane synthesis induced by thrombin and arachidonic acid. When platelets were activated by thrombin, half maximal inhibition (ED50 effective dose of cetiedil necessary for 50% inhibition) for platelet aggregation was 100 microM while that for thromboxane B2 (TXB2) production was 50 microM. When arachidonic acid was used, the ED50 for platelet aggregation was 100 microM while that for TXB2 production was 150 microM. The presence of calcium ions did not affect on the inhibitory effects of cetiedil. The cAMP level in platelets did not increase after incubation with cetiedil. Cetiedil appears to inhibit the activation of platelets related to thromboxane synthesis.

Gas chromatographic analysis of cetiedil, a candidate antisickling agent, in human plasma with nitrogen-sensitive detection

In this report a sensitive gas chromatographic assay for cetiedil, a candidate antisickling agent, in human plasma is described. After a triple extraction procedure, cetiedil was analyzed without derivatization with a nitrogen-phosphorus detector (with papaverine used as the internal standard.) Cetiedil was measured in plasma samples taken from human volunteers administered the drug intravenously.

An analysis of the mechanism by which cetiedil inhibits the Gardos phenomenon

Energy depletion in the human erythrocyte causes a rise in intracellular calcium. This in turn accelerates the transmembrane movement of potassium and chloride, resulting in cell dehydration. This process, known as the Gardos phenomenon, is inhibited by cetiedil. The present study examines the mechanism by which cetiedil inhibits the Gardos phenomenon. The ability of cetiedil to retard the initial step in the Gardos phenomenon, a rise in intracellular calcium, was first tested. Cetiedil did not prevent calcium accumulation. Cetiedil's ability to inhibit anion movement was next evaluated, as cetiedil could appear to be blocking K movement when in fact it was preventing the movement of its accompanying anion. No inhibitory effect on anion movement was seen. Since cetiedil prevented neither calcium accumulation nor anion movement, it must inhibit the Gardos phenomenon by preventing the opening of the K-specific gate in the erythrocyte membrane. The fact that cetiedil's effect on the Gardos phenomenon could not be removed with repeated cell washing indicates that this effect is irreversible.

Decrease of transport of some polyols in sickle cells

This paper reports the results of kinetic studies on the inward net-flux of small non-electrolytes (ethylene glycol, glycerol and erythritol) in sickle cells as compared to normal erythrocytes. Net transport rates were evaluated by turbidimetric measurements for ethylene glycol and glycerol and by hematocrit monitoring for erythritol. A 2-fold and 4-fold reduction in the permeability coefficient for ethylene glycol and glycerol, respectively, were found in sickle cells as compared to normal erythrocytes. In contrast, no significant changes in erythritol transport kinetics were observed. The dependence of glycerol permeability on temperature, pH and oxygenation is the same in both types of cells. A significant correlation was observed between glycerol permeability and cell density only for sickle cells. The results indicate that irreversible modifications of membrane proteins, responsible for the glycerol and ethylene glycol transport, do occur in sickle cells.

Bepridil and cetiedil. Vasodilators which inhibit Ca2+-dependent calmodulin interactions with erythrocyte membranes

Two new vascular smooth muscle relaxants, bepridil and cetiedil, were found to possess specific CaM-inhibitory properties which resembled those of trifluoperazine. Trifluoperazine, bepridil, and cetiedil inhibited Ca2+-dependent 125I-CaM binding to erythrocyte membranes and CaM activation of membrane Ca2+-ATPase with IC50 values of approximately 12, approximately 17, and approximately 40 microM, respectively. This does not appear to be the result of a nonspecific hydrophobic interaction since inhibition was not observed with micromolar concentrations of many other hydrophobic agents. The predominant inhibition of binding and Ca2+-ATPase activation was competitive with respect to CaM. Bepridil and cetiedil bind directly to CaM since these drugs displaced [3H]trifluoperazine from sites on CaM. Inhibition of Ca2+-ATPase and binding by the drugs was not due to interference with the catalytic activity of this enzyme since: (a) neither inhibition of CaM-independent basal Ca2+-ATPase activity nor inhibition of proteolytically-activated Ca2+-ATPase activities were produced by these agents, and (b) no drug-induced inhibition of CaM binding was detected when membranes were preincubated with these agents but washed prior to addition of 125I-CaM. Thus, bepridil and cetiedil competitively inhibit Ca2+-dependent interactions of CaM with erythrocyte membranes, most likely by a direct interaction between these drugs and CaM. The principal clinical actions of these drugs may be explained by their interactions with CaM or CaM-related proteins leading to reduced activation of Ca2+-regulated enzymes in certain other tissues, such as myosin light chain kinase in vascular smooth muscle.

A further characterization of the selective K movements observed in human red blood cells following acetylphenylhydrazine exposure

Following brief exposure to acetylphenylhydrazine, the potassium permeability of the human erythrocyte membrane is selectively augmented. While a similar increase in potassium permeability results from the intracellular accumulation of calcium (the Gardos phenomenon), we have found a number of features that allow these two pathways to be distinguished from one another. The acetylphenylhydrazine pathway does not require calcium for its activation, and can be seen even in the presence of a molar excess of the calcium chelator EGTA. The transmembrane potassium movement via this channel has a specific requirement for the anion chloride, and it can be inhibited by furosemide. The potassium that moves through the Gardos pathway, on the other hand, can be accompanied by any permeant anion, and is inhibitable by quinidine or cetiedil. Thus, acetylphenylhydrazine exposure seems to promote K + Cl cotransport, whereas the Gardos pathway represents a potassium conductive channel. While full demonstration of both these pathways requires harsh in vitro manipulation, the large electrochemical potassium gradient favoring the movement of this cation out from the erythrocyte suggests that even a partial activation of either pathway could cause intracellular dehydration and thus contribute importantly to the pathophysiology of in vivo red cell destruction.

Cetiedil inhibition of calmodulin-stimulated enzyme activity

Cetiedil, an in vitro anti-sickling agent, inhibited calmodulin-stimulated cyclic 3':5'-nucleotide phosphodiesterase (EC 3.1.4.17) and Ca2+-ATPase (ATP phosphohydrolase, EC 3.6.1.3) activities. The drug had no effect on basal enzyme activities in the absence of calmodulin. The inhibition of phosphodiesterase was competitive with respect to the concentrations of both cAMP and calmodulin. Cetiedil did not inhibit calmodulin-stimulated enzyme activities by acting as a calcium chelator, since increasing the concentration of calcium did not reverse the inhibitory effect.

Desickling of sickled erythrocytes by pulsed radio-frequency field

Electric fields were found to deform sickled erythrocytes. When the intensity of applied fields exceeded a threshold value, sickled erythrocytes transformed into a spherical shape. Prolonged application of the field usually caused hemolysis of erythrocytes. Deformation of red blood cells could be partly reversed if the field was turned off at an early stage. The cause of desickling may be the interaction of the field with the erythrocyte membrane and also with gelled intracellular hemoglobin S molecules.

The effect of cell hydration on the deformability of normal and sickle erythrocytes

The deformability of the erythrocyte (RBC) is greatly influenced by its state of hydration. The purpose of this investigation is to quantitate this relationship by measuring the deformability of an RBC population over a broad range of cell water content. By manipulation of the ion content of the RBC, we performed all of the experiments in media which were isotonic with plasma. To raise ion and water content, RBC were incubated in a Li2CO3 medium. To lower cell ion and water content, RBC were exposed to the K ionophore, valinomycin. The range of cell water content achieved during the entire experiment was 900-3200 g/kg cell solid (normal in vivo cell water content being 1800-1950 g/kg cell solid). By using the Ektacytometer, an automated cylindrical viscometer, we were able to measure deformability of the RBC sampled at various points along this range of cell water content. We found that optimal rheologic behavior was exhibited by normal RBC when their water content was in the normal range. A rise or a fall in cell hydration resulted in a decrease in cell deformability. By contrast, the deformability of freshly drawn, well-oxygenated sickle RBC was well below that found for normal RBC. Upon volume expansion, however, the deformability of these sickle RBC improved markedly. This observation suggests that sickle RBC are suboptimally hydrated and that their abnormal rheology is at least in part a consequence of cell dehydration.