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Le chirurgien vasculaire est confronté quotidiennement au phénomène d’ischémie-reperfusion. En effet, toute intervention chirurgicale nécessitant un clampage artériel induit une situation d’ischémie, qui est ensuite suivie d’une reperfusion au moment du déclampage. L’objectif de ce travail est de faire une mise au point sur la physiopathologie de l’ischémie-reperfusion au niveau du muscle squelettique et de dégager des pistes pour prévenir les lésions d’ischémie-reperfusion dans la pratique clinique courante du chirurgien vasculaire. Les mécanismes contribuant aux lésions d’ischémie-reperfusion sont multifactoriels et complexes. La surcharge calcique et le stress oxydant jouent un rôle majeur, conduisant à l’ouverture du pore de transition de perméabilité mitochondrial. Les mitochondries sont donc une cible privilégiée pour lutter contre les lésions d’ischémie-reperfusion. Le conditionnement ischémique est un processus qui tend à lutter contre les effets délétères de l’ischémie-reperfusion. L’idée est en fait de faire subir à l’organisme de brèves séquences répétées d’ischémie-reperfusion, de façon à stimuler les défenses antioxydantes pour lutter contre une ischémie-reperfusion plus conséquente. Bien qu’offrant des résultats prometteurs en expérimentation animale, le conditionnement ischémique a des résultats plus mitigés au niveau clinique. Néanmoins, avec un protocole bien conduit, dans des situations cliniques adaptées, le conditionnement ischémique pourrait avoir une place majeure. Ainsi, s’il s’avère efficace, une vaste application du conditionnement ischémique s’offrirait aux chirurgiens vasculaires.

Les données concernant l’impact respiratoire des patients ayant présenté une infection à SARS-CoV-2 sont très limitées. Dans ce contexte, un suivi cardiorespiratoire de patients hospitalisés pour une infection à SARS-CoV-2, 3 mois après leur sortie d’hospitalisation a été réalisé au sein des services de pneumologie et physiologie des hôpitaux universitaires de Strasbourg.

To examine metabolism during exercise in 2 patients with muscle phosphorylase kinase (PHK) deficiency and to further define the phenotype of this rare glycogen storage disease (GSD).

Heart rate variability (HRV) is a measure of the physiological variation of R-R intervals, reflecting the sympathovagal balance. In both overt and subclinical hyperthyroidism, a relative increase in sympathetic activity has been demonstrated, mainly due to a decrease in vagal activity. The modifications of HRV during orthostatism in normal subjects resemble those seen in hyperthyroidism. We have studied the response of 19 patients with overt hyperthyroidism and 12 with subclinical hyperthyroidism during orthostatism using HRV and compared the results to those of 32 healthy controls. In the three groups, the R-R intervals decreased in the same proportion after orthostatism. The low frequency power (LF)/[LF + high frequency power (HF)] ratio, which reflects the sympathetic tone, also increased in the same proportion in the three groups. However, the mechanisms of the modulation of the sympathovagal balance during orthostatism were different among the three groups. In controls, the relative increase of sympathetic tone after orthostatism was due principally to a decrease in vagal tone (reflected by decreased power in the HF band), while in overt hyperthyroidism, where the power in the HF band was already minimal in the lying position, there was a clear increase in the LF band power during orthostatism. The results were intermediate in the subclinical hyperthyroidism group, reflecting a continuum of effects of the thyroid hormone excess on the autonomic nervous system. Our study shows that despite an apparent normal cardiovascular adaptation to orthostatism in hyperthyroidism, the modulation of the autonomic nervous system is profoundly modified.

This study explores the importance of creatine kinase (CK) in the regulation of muscle mitochondrial respiration in human subjects depending on their level of physical activity. Volunteers were classified as sedentary, active or athletic according to the total activity index as determined by the Baecke questionnaire in combination with maximal oxygen uptake values (peak V̇O2, expressed in ml min−1kg−1). All volunteers underwent a cyclo‐ergometric incremental exercise test to estimate their peak V̇O2and V̇O2at the ventilatory threshold (VT). Muscle biopsy samples were taken from the vastus lateralis and mitochondrial respiration was evaluated in an oxygraph cell on saponin permeabilised muscle fibres in the absence (V̇0) or in the presence (V̇max) of saturating [ADP]. While V̇0was similar, V̇maxdiffered among groups (sedentary, 3.7 ± 0.3, active, 5.9 ± 0.9 and athletic, 7.9 ± 0.5 μmol O2min−1(g dry weight)−1). V̇maxwas correlated with peak V̇O2(P< 0.01, r= 0.63) and with V̇T(P< 0.01, r= 0.57). There was a significantly greater degree of coupling between oxidation and phosphorylation (V̇max/V̇0) in the athletic individuals. The mitochondrial Kmfor ADP was significantly higher in athletic subjects (P< 0.01). Mitochondrial CK (mi‐CK) activation by addition of creatine induced a marked decrease in Kmin athletic individuals only, indicative of an efficient coupling of mi‐CK to ADP rephosphorylation in the athletic subjects only. It is suggested that increasing aerobic performance requires an enhancement of both muscle oxidative capacity and mechanisms of respiratory control, attesting to the importance of temporal co‐ordination of energy fluxes by CK for higher efficacy.

Lethal toxin (LT) from Clostridium sordellii has been shown in HeLa cells to glucosylate and inactivate Ras and Rac and, hence, to disorganize the actin cytoskeleton. In the present work, we demonstrate that LT treatment provokes the same effects in HL-60 cells. We show that guanosine 5'-O-(3-thiotriphosphate)-stimulated phospholipase D (PLD) activity is inhibited in a time- and dose-dependent manner after an overnight treatment with LT. A similar dose response to the toxin was found when PLD activity was stimulated by phorbol 12-myristate 13-acetate via the protein kinase C pathway. The toxin effect on actin organization seemed unlikely to account directly for PLD inhibition as cytochalasin D and iota toxin from Clostridium perfringens E disorganize the actin cytoskeleton without modifying PLD activity. However, the enzyme inhibition and actin cytoskeleton disorganization could both be related to a major decrease observed in phosphatidylinositol 4,5-bisphosphate (PtdIns(4, 5)P2). Likely in a relationship with this decrease, recombinant ADP-ribosylation factor, RhoA, Rac, and RalA were not able to reconstitute PLD activity in LT-treated cells permeabilized and depleted of cytosol. Studies of phosphoinositide kinase activities did not allow us to attribute the decrease in PtdIns(4,5)P2 to inactivation of PtdIns4P 5-kinase. LT was also found to provoke a major inhibition in phosphatidylinositol 3-kinase that could not account for the inhibition of PLD activity because wortmannin, at doses that fully inhibit phosphatidylinositol 3-kinase, had no effect on the phospholipase activity. Among the three small G-proteins, Ras, Rac, and RalA, inactivated by LT and involved in PLD regulation, inactivation of Ral proteins appeared to be responsible for PLD inhibition as LT toxin (strain 9048) unable to glucosylate Ral proteins did not modify PLD activity. In HL-60 cells, LT treatment appeared also to modify cytosol components in relationship with PLD inhibition as a cytosol prepared from LT-treated cells was less efficient than one from control HL-60 cells in stimulating PLD activity. Phosphatidylinositol transfer proteins involved in the regulation of polyphosphoinositides and ADP-ribosylation factor, a major cytosolic PLD activator in HL-60 cells, were unchanged, whereas the level of cytosolic protein kinase Calpha was decreased after LT treatment. We conclude that in HL-60 cells, lethal toxin from C. sordellii, in inactivating small G-proteins involved in PLD regulation, provokes major modifications at the membrane and the cytosol levels that participate in the inhibition of PLD activity. Although Ral appeared to play an essential role in PLD activity, we discuss the role of other small G-proteins inactivated by LT in the different modifications observed in HL-60 cells.

Objectives:to characterise the impact of the crimping of polyester prostheses on the fluid flow kinetics. Design:an experimental in vitrostudy. Materials and methods:we investigated four models of polyester vascular prostheses in a continuous laminar flow circuit. The flow velocity was 80 ml/s for all experiments. We studied two fluids of different viscosity within the circuit. The speed of the particles was measured by a laser Doppler anemometer 2 to 52 mm from the prosthetic interface. We first established a calibrated flow-velocity profile corresponding to the study of the support inside the circuit without any prosthesis. We measured the velocity profiles for each prosthesis corresponding to four crimp densities obtained by stretching the grafts. Results:the crimping of PET textile prostheses led to a decrease of flow velocity especially closer to the prosthetic surface. The decrease of flow velocity was dependent on the model of prosthesis. This decrease of flow velocity is described by the following negative exponential law: ΔV=a·b−xwhere (a) is the crimp density and (b) the fluid viscosity. Conclusions:flow velocity near a prosthetic surface is influenced by the morphology of the crimping. The impact of crimping on the flow velocity in a vascular prosthesis can be predicted by computer simulation models. This may provide the optimal shape of crimping for each prosthesis.

Activation of phosphoinositide‐specific phospholipase C (PLC) generates two intracellular signals which play major roles in many cellular processes including secretion, proliferation and contraction. PLC activation by many receptors occurs via a guanine nucleotide regulatory protein, Gp. PLCs are found predominantly in the cytosolic fraction though some activity is membrane‐associated. At least four families of iso‐enzymes of PLC (alpha, beta, gamma and delta) have been identified, but there is only scant evidence to indicate that any of the mammalian cytosolic activities are involved in G‐protein‐regulated signalling. In this study we demonstrate that the PLC activity from rat brain cytosol can be regulated in a G‐protein‐dependent manner in a reconstituted system using pre‐permeabilized HL60 cells. We identify two enzymes, PLC‐beta and a novel 86 kDa enzyme (designated PLC‐epsilon) as the G‐protein‐regulated enzymes. PLC‐epsilon was found to be the major G‐protein‐regulated enzyme.

Cardiac transplant patients manifest several haemodynamic changes as well as altered peripheral responses to exercise which may disrupt body fluid regulation. This study examined the effect on an endurance training programme on the exercise-induced hydromineral endocrine responses of heart transplant patients. Seven patients underwent a square-wave exercise test before and after a 6-week training programme. The tests were performed at the same absolute intensity but, during training, the workload was increased to maintain the same relative exercise intensity. Pretraining results were compared to those obtained from agematched controls. Training improved physical capacity, producing a significant increase in maximal tolerated power and workload between the first and last training session (P< 0.05, P< 0.001, respectively). Haematocrit and osmolality were increased in both groups at the end of exercise (P< 0.01) but changes observed post-training did not differ from pretraining values. Apart from atrial natriuretic peptide (ANP), which showed significantly higher concentrations at rest and during exercise (P< 0.01), the changes in hydromineral hormones of the patients resembled those of the controls. Basal plasma renin activity (PRA) was slightly raised prior to training (P< 0.07) compared to the controls and post-training. For both PRA and aldosterone, a significant training effect was revealed when both the exercise-stimulated increase and postexercise decline were considered (P< 0.05), possibly reflecting lower noradrenaline concentrations. Training had no effect on either basal or exercise stimulated ANP levels, which is compatible with the theory that ANP regulation is largely under mechanical rather than sympathetic nervous system control. Mean arginine vasopressin concentrations in the patients were not increased, possibly due to inhibitory effects of immunosuppressive glucocorticoids combined with the large variation in response observed, particularly for the untrained patients. In summary, these results showed that despite cardiac denervation, the heart transplant patients demonstrated effective body fluid regulatory endocrine responses during exercise and that although training produced substantial improvement in their physical capacity, it was accompanied by only subtle changes in hydromineral hormones.

Abstract.: Dictyostelium discoideum cells are highly resis tant to xenobiotics. We previously observed that these primitive eukaryotic cells contain a 170-kDa P-glycoprotein, mediating multidrug resistance in mammalian cells, but nonfunctional in Dictyostelium cells. We show here that D. discoideum cells vitally stained with the DNA-specific dye, Hoechst 33342, release fluorescent material in their culture medium. Electron microscopy and lipid analysis demonstrate the vesicular nature of this material. Moreover, nucleic acids associate with these extracellular vesicles independently of Hoechst vital staining. The main vesicular DNA component exhibits a size >21 kb. Shedding of microvesicles during cell growth is not concomitant with programmed cell death. We propose that these extracellular vesicles are involved in a new cellular resistance mechanism against xenobiotics. Furthermore, since the association of DNA with vesicles occurs in physiological growth conditions and independently of vital staining, the new shedding process might be involved in a more general intercellular mechanism.

Cardiac transplant patients manifest several haemodynamic changes as well as altered peripheral responses to exercise which may disrupt body fluid regulation. This study examined the effect on an endurance training programme on the exercise-induced hydromineral endocrine responses of heart transplant patients. Seven patients underwent a square-wave exercise test before and after a 6-week training programme. The tests were performed at the same absolute intensity but, during training, the workload was increased to maintain the same relative exercise intensity. Pretraining results were compared to those obtained from agematched controls. Training improved physical capacity, producing a significant increase in maximal tolerated power and workload between the first and last training session (P < 0.05, P < 0.001, respectively). Haematocrit and osmolality were increased in both groups at the end of exercise (P < 0.01) but changes observed post-training did not differ from pretraining values. Apart from atrial natriuretic peptide (ANP), which showed significantly higher concentrations at rest and during exercise (P < 0.01), the changes in hydromineral hormones of the patients resembled those of the controls. Basal plasma renin activity (PRA) was slightly raised prior to training (P < 0.07) compared to the controls and post-training. For both PRA and aldosterone, a significant training effect was revealed when both the exercise-stimulated increase and postexercise decline were considered (P < 0.05), possibly reflecting lower noradrenaline concentrations. Training had no effect on either basal or exercise stimulated ANP levels, which is compatible with the theory that ANP regulation is largely under mechanical rather than sympathetic nervous system control. Mean arginine vasopressin concentrations in the patients were not increased, possibly due to inhibitory effects of immunosuppressive glucocorticoids combined with the large variation in response observed, particularly for the untrained patients. In summary, these results showed that despite cardiac denervation, the heart transplant patients demonstrated effective body fluid regulatory endocrine responses during exercise and that although training produced substantial improvement in their physical capacity, it was accompanied by only subtle changes in hydromineral hormones.

The survival rate of heart transplant patients has increased considerably since the development of new immunosuppressive drugs. In the long term, however, cardiac transplantation results in a high incidence of osteoporosis which represents a major functional handicap. To examine whether patients in the early stages have impaired phosphocalcic metabolism, intact parathyroid hormone (PTH 1–84), native osteocalcin, ionized Ca++ and pH were measured at rest and during muscular exercises a dynamic test used to override circadian and ultradian PTH variations. A group of 12 patients receiving the usual immunosuppressive therapy, which is mainly an association of cyclosporin and prednisolone, and 8 sedentary control subjects performed a square-wave endurance test at the same relative intensity for 30 min. No patient had previous bone disease and the period since transplantation was 12.2 ± 2.7 months. For the transplant patients, initial PTH concentrations and responses to exercise were higher (P < 0.01) compared to the control subjects with a dramatic increase after 10 min of recovery. From higher (P < 0.001) resting concentrations, osteocalcin further increased during exercise (P < 0.01) in the heart transplant group but not in the control subjects. In both groups pH showed the same time-course with a rapid fall during exercise (P < 0.05) and Ca++ concentrations increased during the exercise period. (P < 0.01 for patients;P < 0.05 for controls) with a significant fall in both groups after 10 min of recovery (P < 0.01). Despite a tendency for initial Ca++ concentrations to be lower in the patients (P < 0.07), there were no significant differences between both groups either for pH or for Ca++. These results show that in the early stage of transplantation, the patients under immunosuppressive therapy have moderate hyperparathyroidism which precedes the serious complications of bone loss in long-term transplant patients.

Activation of phosphoinositide‐specific phospholipase C (PLC) generates two intracellular signals which play major roles in many cellular processes including secretion, proliferation and contraction. PLC activation by many receptors occurs via a guanine nucleotide regulatory protein, Gp. PLCs are found predominantly in the cytosolic fraction though some activity is membrane‐associated. At least four families of iso‐enzymes of PLC (alpha, beta, gamma and delta) have been identified, but there is only scant evidence to indicate that any of the mammalian cytosolic activities are involved in G‐protein‐regulated signalling. In this study we demonstrate that the PLC activity from rat brain cytosol can be regulated in a G‐protein‐dependent manner in a reconstituted system using pre‐permeabilized HL60 cells. We identify two enzymes, PLC‐beta and a novel 86 kDa enzyme (designated PLC‐epsilon) as the G‐protein‐regulated enzymes. PLC‐epsilon was found to be the major G‐protein‐regulated enzyme.

Annexin III, a putative inositol (1,2)-phosphohydrolase, was co-crystallized with inositol 2-phosphate, the inhibitor of the reaction, and its structure was solved to 1.95 A resolution. No enzyme active site was observed in the structure. Assays for enzymatic activity were also negative. Search for annexin III-inositol phosphate interactions using the BIAcoreTM system revealed an affinity for inositol cyclic (1,2)-phosphate, suggesting annexin III may sequester the molecule in the cell. The BIAcoreTM system used with different phospholipids showed that annexin III displays specificity for phosphatidylethanolamine, but not for phosphatidylinositols. Interestingly, a molecule of ethanolamine was found bound to the protein in the crystal structure. Coupled with the fact that this is a particularly abundant phospholipid in granules specific to neutrophils, cells where annexin III is highly expressed, our finding could be pointing to a physiological role of annexin III.

Stimulation of phospholipase D (PLD) by cell surface receptors has been observed in many cell types. We have investigated the mechanism of activation of this enzyme in undifferentiated HL60 cells. GTP analogues and Ca2+ (buffered in the nanomolar to micromolar range) were introduced into HL60 cells in the presence of the permeabilizing agent, streptolysin O. We report that guanosine 5′-[gamma-thio]triphosphate (GTP[S]) is a potent activator of phospholipase D when Ca2+ is available at micromolar levels. Phorbol 12-myristate 13-acetate or Ca2+ alone can also stimulate PLD, but to a limited extent. The activation of PLD by GTP[S] can be partially dissociated from GTP[S]-stimulated phosphoinositide-specific phospholipase C, suggesting that a G-protein may be directly involved in regulating PLD. However, maximal activation of PLD only occurs under conditions that are permissive to phospholipase C stimulation. We conclude that PLD activation is under dual control, i.e. protein kinase C- as well as G-protein-mediated regulation. Synergistic activation occurs when both pathways are simultaneously stimulated. We conclude that full activation of PLD requires protein kinase C, increased Ca2+ and a GTP-binding protein. Evidence for cytosolic components that may also be involved in obtaining full activation of PLD is also presented.

The increase in plasma concentration of atrial natriuretic factor in heart transplant patients has not been fully elucidated. Besides an eventual pressure or volume overload leading to passive atrial distension, the atrial tension developed during atrial systole, or atrial ejection force, which may be increased by the transplantation procedure, is an important determinant of atrial natriuretic factor release. We therefore determined the plasma concentration of atrial natriuretic factor and the maximal atrial ejection force in 15 heart transplant patients and 8 controls, matched for age and body mass. Atrial ejection force, as defined as the force exerted by the left atrium to accelerate blood into the left ventricle during atrial systole, was obtained using combined two-dimensional imaging and doppler echocardiography. Serum creatinin concentrations, heart rate [91.9 (SD 13.2) vs 71.8 (SD 10.9) beats · min-1], mean arterial blood pressure [103.9 (SD 9.8) vs 87.4 (SD 5.8) mmHg, 13.85 (SD 1.31) vs 11.65 (SD 0.77) kPa], left ventricular posterior wall thickness and interventricular septum thickness were higher in heart transplant patients compared to controls. Plasma concentration of atrial natriuretic factor was also elevated in heart transplant patients [63.9 (SD 18.1) vs 34.0 (SD 3.2) pg · ml-1; P<0.001]. In contrast, although the left atrial area was greater in heart transplant patients [28.2 (SD 4.8) vs 15.8 (SD 2.5) cm2; P<0.001], mitral area, transmitral Doppler A-wave maximal velocity and atrial ejection force were similar in transplant and in control patients [7.7 (SD 3.5) vs 8.9 (SD 2.8) kdyn, 77 (SD 35) vs 89 (SD 28) mN]. No significant correlation was observed between concentration of atrial natriuretic factor and atrial ejection force, either in heart transplant patients or in controls. Thus, the elevated plasma concentration of atrial natriuretic factor observed in these heart transplant patients was multifactorial in origin, and was considered to depend upon an hypersecretion rather than upon a decreased clearance rate. Moreover, it is suggested that the atrial ejection force was unlikely to have participated in this enhanced release of atrial natriuretic factor.

Annexin V belongs to a family of proteins that interact with phospholipids in a Ca2+-dependent manner. This protein has been demonstrated to have anti-phospholipase A2 activity. However, this effect has never yet been reported with the 85-kDa cytosolic PLA2 (cPLA2). We studied, in a model of differentiated and streptolysin O-permeabilized HL-60 cells, the effect of annexin V on cPLA2 activity after stimulation by calcium, GTPgammaS (guanosine 5'-O-(3-thiotriphosphate)), formyl-Met-Leu-Phe, or phorbol 12-myristate 13-acetate. Both recombinant and human placental purified annexin V inhibit cPLA2 activity whatever the stimulus used. The decrease of arachidonic acid release is of 40 and 50%, respectively, at [Ca2+] of 3 and 10 microM. The mechanism of inhibition was also analyzed. cPLA2 requires calcium and protein kinase C (PKC) or mitogen-activated protein kinase phosphorylation for its activation. As annexin V was shown to be an endogenous inhibitor of PKC, PKC-stimulated cPLA2 activity was analyzed. Using GF109203x, a specific PKC inhibitor, we demonstrated that this pathway is of minor importance in our model. cPLA2 inhibition by annexin V is not linked to PKC inhibition. To test the hypothesis of phospholipid depletion, mutants of annexin V were constructed using mutagenesis directed to Ca2+ site. We demonstrate that the Ca2+ site located in domain I is necessary for the inhibitory effect of annexin V on cPLA2 activity. The site in domain IV is also involved but with less efficiency. In contrast, mutations in site II and III do not modify this effect. Moreover, annexin V mutated on all sites does not inhibit cPLA2. Thus, we propose a predominant role of module (I/IV) in the biological action of annexin V, which, in physiological conditions, may control cPLA2 activity by depletion of the phospholipid substrate.

Alpha-1 adrenergic receptors were examined in both inner and outer layers of human pregnant myometrium using radioligand binding of [3H]prazosin. [3H]prazosin bound rapidly and reversibly to a single class of high affinity binding sites in myometrial membrane preparations. Scatchard analysis gave similar values of equilibrium dissociation constants in both myometrial layers. In contrast, more alpha-1 adrenergic receptors were detected in the outer layer than in the inner layer. Antagonist inhibited [3H]prazosin binding with an order of potency of prazosin greater than phentolamine greater than idazoxan. Competition experiments have also revealed that a stable guanine nucleotide decreases the apparent affinity of norepinephrine for myometrial [3H]prazosin binding sites. The functional status of these alpha-1 adrenergic receptors was also assessed by measuring the norepinephrine-induced accumulation of inositol phosphates in myometrial tissue. Norepinephrine produced a concentration-dependent accumulation of inositol phosphates in both myometrial layers. However, norepinephrine-induced increases in inositol 1,4,5-triphosphate were only observed in the outer layer. These results indicate that alpha-1 adrenergic receptors in human myometrium at the end of pregnancy are linked to phosphoinositide hydrolysis and that this response occurs mainly in the outer layer.

When HL-60 cells were induced to differentiate into granulocyte-like cells by culture in the presence of 1.3% dimethyl sulfoxide, an increase in the rate of ouabain-sensitive 86Rb transport was observed during the first 6 h followed by a constant decrease which became stable on day 4 at about 40% of control level. By contrast, the number of ouabain binding sites remained constant during the first 24 h then decreased with the same kinetics as that of the 86Rb transport rate. These results suggest that alterations in ionic fluxes, through activation of the sodium pump, are part of the early events resulting in HL-60 cell differentiation.

Retinoic acid, which induces the differentiation of HL 60 cells to granulocytes, produces a cell alkalinization from pHi = 7.03 to pHi = 7.37. The half-maximum effect of retinoic acid is observed at 10 nM. The effect of retinoic acid on the pHi develops slowly, and it precedes the differentiation of the cells. A cell alkalinization is also observed after differentiation of the cells by dimethyl sulfoxide. It is not observed using etretinate, a synthetic retinoid that does not promote the differentiation of HL 60 cells. Two pHi regulating mechanisms coexist in HL 60 cells. The Na+/H+ exchange system is the major mechanism that allows HL 60 cells to recover from an intracellular acidosis. A second mechanism is a Na-HCO3 cotransport system. During differentiation of the cells by retinoic acid, a 2-fold increase in the activity of the Na+/H+ exchange system is observed, while the activity of the NaHCO3 cotransport remains constant. The properties of interaction of the Na+/H+ exchanger with internal H+, external Na+, and Li+ as well as with amiloride and its derivatives are defined. The Na+/H+ exchanger of HL 60 cells is characterized by unusually low affinities for alkali cations and a high affinity for amiloride and its derivatives. The pHi dependence of the exchanger is not modified after differentiation by retinoic acid. It is concluded that the mechanism of activation of the Na+/H+ exchanger by retinoic acid is distinct from the short-term effect produced by mitogens and phorbol esters which change the pHi dependence of the system.

When HL‐60 cells were induced to differentiate into granulocyte‐like cells by culture in the presence of 1.3% dimethyl sulfoxide, an increase in the rate of ouabain‐sensitive 86Rb transport was observed during the first 6 h followed by a constant decrease which became stable on day 4 at about 40% of control level. By contrast, the number of ouabain binding sites remained constant during the first 24 h then decreased with the same kinetics as that of the 86Rb transport rate. These results suggest that alterations in ionic fluxes, through activation of the sodium pump, are part of the early events resulting in HL‐60 cell differentiation.