Phosphate metabolism in erythrocytes of critically ill patients

Orthophosphate (Pi), adenosine 5'-diphosphate (ADP), adenosine 5'-triphosphate (ATP) and 2,3-diphosphoglycerate (2,3-DPG) were measured in the erythrocytes of patients in an intensive care unit. The patients' plasma concentration of Pi varied from 0.1 to 4.2 mmol/l, and the corresponding concentration in erythrocytes varied from 0.1 to 2.0 mmol/litre of cells. Marked ATP depletion (less than 1 mmol/litre of cells) was only observed when erythrocyte Pi was less than 0.3 mmol/litre of cells and plasma Pi was less than 0.35 mmol/l. No dependence of 2,3-DPG concentration on the cellular concentration of Pi was detected. The phosphorylation potential [ATP]/([ADP] X [Pi]) varied inversely with the erythrocyte concentration of Pi. Hence the calculated free energy of hydrolysis of ATP in the cell increased from -58 kJ/mol in the most hypophosphataemic samples to -51 kJ/mol in the most hyperphosphataemic. Such changes may adversely affect cell function by altering the steady state mass-action ratios of ATPase reactions. When erythrocytes from normal donors were incubated in solutions containing 1 or 5 mmol/l Pi, the cellular concentrations of Pi stabilized at 1.09 and 2.85 mmol/litre of cells respectively. The corresponding rates of lactate production were 2.09 and 3.11 mmol h-1 litre-1 of cells. In spite of this stimulation of glycolysis (and hence of the flux through ATP synthesizing steps of the Embden-Meyerhof pathway), no significant change in ATP concentration was observed. As in the patients' cells, this indicates that, when extracellular Pi concentrations are perturbed, the concentrations, in erythrocytes, of organic phosphates are more closely regulated than the concentration of Pi.

Experimental investigation of the rheological activation of blood platelets

In order to define various aspects of platelet rheological activation, samples of whole blood and platelet-rich plasma (PRP) from the same donors were subjected for 5 min to shear rates increasing from 10 to 10000 sec-1 (shear stresses from 10(-2) to 30 Pa approximatively) in a Couette type viscometer. The following parameters were measured: erythrocyte hemolysis; lactic dehydrogenase activity; plasma B-Thromboglobulin (B-TG); adenine nucleotides, and platelet photometric aggregation. The experimental results reveal that: In whole blood, hemolysis only reached at maximum 2% of the total hemolysis. Plasma LDH activity increased regularly beyond 500 sec-1, in close correlation with B-TG plasma concentration. In contrast, ADP and ATP levels remained stable up to 1000 sec-1 then increased slowly. In PRP, the LDH, ADP and ATP levels remain practically stable up to shear rates around 5000 sec-1. In contrast, B-TG appeared to be released in plasma at shear rate values of 3000 sec-1 and its progression is only correlated with the other parameters, when the platelet lysis occurred. Finally, a rapid and complete inhibition of platelet aggregation to ADP was observed from 5000 sec-1.

The use of a platelet nucleotide assay as a possible diagnostic test for malignant hyperthermia

A bioassay, using high-performance liquid chromatography (HPLC) analysis of platelet adenosine nucleotides and hypoxanthine, was studied for its potential use as a test for MH susceptibility. A protocol for the assay was developed, based on the method outlined by Solomons and Masson. The HPLC procedure was a rapid, efficient, sensitive, and highly reproducible technique for measuring ATP, ADP, AMP, and hypoxanthine in platelets. Conditions of extraction and storage were critical for preventing degradation of the nucleotides. Extraction of nucleotides at icebath temperature was found necessary. Storage of platelet extract in PCA, even at -20 degrees C, showed loss of ATP and ADP; hence, neutralization with KOH was essential before storage. Contrary to the findings of Solomons et al., the present study demonstrated that neither ATP depletion nor per cent reduction in nucleotide ratios in platelets treated with halothane can be used as a definitive test for the diagnosis of MH susceptibility. The reason for this disagreement is unclear; however, differences in methods and altitude are implicated. It is possible that the platelet is not affected by malignant hyperthermia and thus cannot serve as a test system for the detection of the syndrome.

Platelet size and shape in hereditary giant platelet syndromes on blood smear and in suspension: evidence for two types of abnormalities

Platelet size on blood smear is compared with platelet size and shape in suspension (i.e., whole blood and citrated platelet-rich plasma [PRP]) for normal donors and 16 patients with hereditary "giant" platelet syndromes (HGPS), including Bernard-Soulier syndrome (BSS) (seven patients), Montreal platelet syndrome (MPS) (three patients), May-Hegglin anomaly (one patient) and Rafael platelet defect (one patient). In whole blood platelet shape is normal for HGPS, but in PRP for 10 of 16 patients with HGPS there is a decrease in the proportion of smooth, discoid-shaped platelets (discocytes [D]). The platelets of all patients with HGPS had abnormally large mean volume (VT) and increased size on peripheral blood smear. Furthermore, 12 of 16 patients with HGPS, including six of seven donors with BSS, had abnormally large discocytes. The measured size of HGPS shape-changed platelets was compared with the size predicted from the size of the D by assuming that the relationship between the size of shape-changed platelets and D was the same as observed for normal donors. In this manner it was shown that for all donors with BSS and MPS, the shape-changed platelets are disproportionately larger than the D. In contrast, in the remaining patients with HGPS the size of the shape-changed platelets was consistent with the size predicted from the D. Examination of VT for MPS as a function of time after addition of 10 mumol/L adenosine diphosphate to PRP revealed an abnormal time course, thereby pointing to an abnormality in the mechanisms that regulate platelet size during shape change. With the lone exceptions of BSS and MPS, the size of platelets on blood smear was well correlated with the total platelet plasma membrane surface area as measured by the osmotic spherocyte method. Our observations point to two distinct abnormalities in platelet size in HGPS: a disproportion between the size of D and "shape-changed" platelets, which may be related to an abnormal shape change and which is observed only for MPS and BSS, and an abnormal increase in platelet size on blood smear, which appears to reflect the increased amount of platelet plasma membrane in other HGPS platelets.

Highly efficient induction of human platelet aggregation in heparinized platelet-rich plasma by diadenosine triphosphate (Ap3A)

Diadenosine triphosphate (Ap3A), which is a releasable dinucleotide of human platelets, induces platelet aggregation when added to heparinized platelet-rich plasma. The concentration dependence of the dinucleotide is similar to ADP. This finding is fully compatible with our recent report of the low potency of Ap3A in citrated platelet-rich plasma relative to ADP. The aggregatory effect of Ap3A in heparinized versus citrated plasma is reflected in the corresponding rates of Ap3A degradation. In citrated plasma, the hydrolysis of Ap3A is drastically slowed down because the hydrolase needs divalent metal ions. The results strongly support the assumption that the aggregatory effect of Ap3A is mediated by the enzymatic hydrolysis of Ap3A which generates ADP as the ultimate stimulus.

Adenine nucleotide concentrations in patients with erythrocyte autoantibodies

Erythrocyte adenine nucleotide concentrations were measured in 154 patients with erythrocyte autoantibodies and 811 normal subjects using a luciferin-luciferase bioluminescent assay. The patients were initially divided into haemolysing and non-haemolysing groups. Red cell adenosine triphosphate (ATP) concentrations were significantly raised in the 96 patients with active haemolysis compared with the normal subjects and with the 58 patients in the non-haemolysing group. Although the patients categorised as non-haemolysing had higher ATP values than the normal subjects, this was because several patients had the anaemia of chronic disorders, which is associated with a shortened red cell life. Measurement of red cell ATP was a useful indicator of mean erythrocyte age and a raised value in patients with erythrocyte autoantibodies reflected active haemolysis.

Simultaneous extraction and reverse-phase high-performance liquid chromatographic determination of adenine and pyridine nucleotides in human red blood cells

A simple and rapid method for the determination of ATP, ADP, AMP, NADP+, NAD+, NADPH, and NADH in human erythrocytes is described. A single-step extraction procedure employing alkaline medium and CF 50A Amicon ultrafiltration membranes allows a simultaneous and total recovery of the compounds of interest. Analysis is performed by reverse-phase high-performance liquid chromatography on a 5-micron Supelcosil LC-18 column and uv detection. Extraction and analysis require about 30 min. Levels of adenine and pyridine nucleotides in normal adults are also presented.

Red blood cell adenine nucleotides abnormalities in Down syndrome

The red blood cell adenine nucleotides of 20 Down Syndrome patients and 20 healthy controls were determined by a new high-performance liquid chromatography method. All patients showed increased concentrations of adenosine 5'-diphosphate (ADP) and adenosine 5'-monophosphate (AMP), while adenosine 5'-triphosphate (ATP), nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP+) were within normal ranges. This alternation of the energetic charge could be partly responsible for the impairment of glucose metabolism in these patients.

Abnormal release of storage pool adenine nucleotides from platelets of dogs affected with basset hound hereditary thrombopathy

Platelets from dogs affected with Basset Hound Hereditary Thrombopathy (BHT), have a thrombasthenia-like aggregation defect but release storage pool ATP in quantities not significantly different from normal controls or BHT heterozygotes when stimulated with 1 X 10(-5)M ADP and 0.22 U/ml thrombin. However, the release occurs so rapidly in the BHT platelets stimulated with ADP that it is complete in approximately one-sixth of the time required for release from normal control and heterozygote platelets. Sequential electron micrographs reveal early release of BHT dense body constituents 30 seconds after stimulation with 1 X 10(-5)M ADP while resting BHT morphology is indistinguishable from normal control animals.

Hemoglobin, hematology, intraerythrocytic phosphates and whole blood Bohr effect from lotic and lentic Hypostomus regani populations (São Paulo-Brasil)

Hemoglobin electrophoretic pattern, whole blood Bohr effect, intraerythrocytic phosphates and some hematological parameters were determined and compared between lotic and lentic Hypostomus regani specimens. The electrophoretic patterns of specimens from both kinds of environments showed four anodic fractions. The relative concentration of the fraction I (the most anodal) is significantly different between specimens from lotic and lentic ambients. Both lentic and lotic specimens presented a low Bohr effect: phi = -0.012 to lentic habitat and phi = -0.187 to lotic one. ATP/GTP ratio are higher than 1.0 for lotic environment specimens and lower than 1.0 for lentic ones.

The platelet defect in acute myeloid leukaemia

In a study of platelets from 13 patients with acute myeloid leukaemia abnormal aggregation and release reactions were found. A previously unrecognised quantitative defect of thromboxane B2 production may, at least in part, explain these findings. In contrast to a previous report, we were unable to show a convincing storage pool defect in these platelets. The platelet membrane glycoproteins were largely normal.

ATP, ADP and AMP in plasma from peripheral venous blood

ATP, ADP and AMP in concentrations at least 1 mumol/l have been found by high pressure liquid chromatography (HPLC) in plasma from peripheral venous blood. Total adenine nucleotide concentrations of about 15-20 mumol/l can be found in some conventional clinical samples of blood using EDTA as an anticoagulant. EDTA prevented adenine nucleotide conversion to inosine in plasma. In order to estimate concentrations in vivo, the contribution derived from the cell breakage inherent even in careful venous blood sampling has been estimated by extrapolation to zero 'haemoglobin' concentration in plasma and minimum values in samples of small volume. Available results appear to be consistent with the release of small amounts of ATP in or near the peripheral circulation at the time of venepuncture. In CSF, ATP, ADP and AMP concentrations were less than 0.05 mumol/l suggesting that membrane activity in the central nervous system is not associated with non-specific leakage. The high Km variant of lymphocyte ecto-5'-nucleotidase was not associated with a significantly higher concentration of its substrate AMP in plasma. However, this enzyme may function on the lymphocyte in the thymus and spleen.

Platelet secretion defect associated with impaired liberation of arachidonic acid and normal myosin light chain phosphorylation

We describe four patients with impaired platelet aggregation and 14C-serotonin secretion during stimulation with adenosine diphosphate (ADP), epinephrine, collagen, and platelet-activating factor. The response to arachidonic acid was normal in all patients with regard to aggregation and in three of the four with regard to 14C-serotonin secretion. The total platelet adenosine triphosphate (ATP) and ADP content and the ATP to ADP ratio was normal in all patients, thereby excluding storage pool deficiency as the cause of the secretion defect. Studies with 3H-arachidonic acid-labeled platelets revealed that the thrombin-induced liberation of arachidonic acid from membrane-bound phospholipids was impaired in these patients. Further, platelet thromboxane B2 production, measured using a radioimmunoassay, was diminished during stimulation with ADP and thrombin, but was normal with arachidonic acid, indicating that the oxygenation of arachidonic acid was normal and that the diminished thromboxane production was due to a defect in the liberation of arachidonic acid. Release of arachidonic acid is mediated by phospholipases that are Ca++ dependent. To examine whether these patients may have a defect in making intracellular Ca++ available, another Ca++-dependent process, myosin light chain phosphorylation, was studied during thrombin stimulation. Platelets from three of the patients were found to behave the same as normal ones, suggesting that the deficiency in phospholipase activity may not be due to impaired Ca++ mobilization. Our studies demonstrate a novel group of patients with platelet secretion defects associated with impaired liberation of arachidonic acid from phospholipids. These patients exemplify a congenital defect, other than deficiencies of cyclooxygenase and thromboxane synthetase, by which thromboxane production may be impaired in platelets.

[Determination of the energy load of erythrocytes in long-distance and medium-distance runners]

In this study erythrocytes drawn from well-trained athletes (middle- and long-distance runners) and from sedentary subjects have been compared for their adenine nucleotide contents. ADP and AMP appeared to be significantly (p less than 0,001) increased only in red cells from athletes in the rest state. After athletes' race this difference with control subjects become insignificant. Nevertheless, the observed ADP and AMP modifications are not great enough to influence the energy charge (CE) of the compared erythrocytes.

Tight coupling of thrombin-induced acid hydrolase secretion and phosphatidate synthesis to receptor occupancy in human platelets

Human platelets incubated with [32P]Pi and [3H]arachidonate were transferred to a Pi-free Tyrode's solution by gel filtration. The labile phosphoryl groups of ATP and ADP as well as Pi in the metabolic pool of these platelets had equal specific radioactivity which was identical to that of[32P]phosphatidate formed during treatment of the cells with thrombin for 5 min. Therefore, the 32P radioactivity of phosphatidate was a true, relative measure for its mass. The thrombin-induced formation of[32P]-phosphatidate had the same time course and dose-response relationships as the concurrent secretion of acid hydrolases. 125I-alpha-Thrombin bound maximally to the platelets within 13s and was rapidly dissociated from the cells by hirudin; readdition of excess 125I-alpha-thrombin caused rapid rebinding of radioligand. This binding-dissociation-rebinding sequence was paralleled by a concerted start-stop-restart of phosphatidate formation and acid hydrolase secretion. [3H]Phosphatidylinositol disappearance was initiated upon binding but little affected by thrombin dissociation and rebinding. ATP deprivation caused similar changes in the time courses for [32P]-phosphatidate formation and acid hydrolase secretion which were different from those of [3H]phosphatidylinositol disappearance. The metabolic stress did not alter the magnitude (15%) of the initial decrease in phosphatidylinositol-4,5-bis[32P]phosphate, but did abolish the subsequent increase of phosphatidylinositol-4,5-bis[32P]-phosphate in the thrombin-treated platelets. It is concluded that in thrombin-treated platelets (1) phosphatidate synthesis, but not phosphatidylinositol disappearance, is tightly coupled to receptor occupancy and acid hydrolase secretion in platelets, (2) successive phosphorylations to phosphatidylinositol-4,5-bisphosphate is unlikely to be the main mechanism for phosphatidylinositol disappearance, and (3) only a small fraction (15%) of phosphatidylinositol-4,5-bisphosphate is susceptible to hydrolysis.

Activation of human platelet phospholipase C by ionophore A23187 is totally dependent upon cyclo-oxygenase products and ADP

Human platelets exposed to the Ca2+ ionophore A23187 form cyclo-oxygenase metabolites from liberated arachidonic acid and secrete dense granule substituents such as ADP. I have shown previously that A23187 causes activation of phospholipase A2 and some stimulation of phospholipase C. I now report that, in contrast to the case for thrombin, the activation of phospholipase C in response to ionophore is completely dependent upon the formation of cyclo-oxygenase products and the presence of ADP. The addition of A23187 to human platelets induces a transient drop in the amount of phosphatidylinositol 4,5-bisphosphate, a decrease in the amount of phosphatidylinositol, and the formation of diacylglycerol and phosphatidic acid. In addition, lysophosphatidylinositol and free arachidonic acid are produced. The presence of cyclo-oxygenase inhibitors or agents which remove ADP partially impairs these changes. When both types of inhibitor are present, the changes in phosphatidylinositol 4,5-bisphosphate and the formation of diacylglycerol and phosphatidic acid are blocked entirely, whereas formation of lysophosphatidylinositol and free arachidonic acid are relatively unaffected. The prostaglandin H2 analogue U46619 activates phospholipase C. This stimulation is inhibited partially by competitors for ADP. I conclude that phospholipase C is not activated by Ca2+ in the platelet, and suggest that stimulation is totally dependent upon a receptor coupled event.

ADP-dependent common receptor mechanism for binding of von Willebrand factor and fibrinogen to human platelets

Human von Willebrand factor (vWF) and fibrinogen are adhesive plasma glycoproteins essential for formation of a platelet hemostatic plug. We investigated the role of ADP and fibrinogen in binding of vWF to platelets in vitro. Binding of 125I-labeled vWF to human platelets separated from plasma proteins and treated with ADP was specific, and time and concentration dependent, reaching equilibrium at 20 min and approaching saturation at 12 micrograms/ml. The binding was inhibited by EDTA and by prostaglandin I2, a known activator of platelet adenylate cyclase. A purine nucleotide affinity analog, 5'-p-fluorosulfonylbenzoyl adenosine (FSBA), which covalently modifies the ADP binding sites on the human platelet membrane, prevented binding of vWF induced with ADP, as well as with human thrombin and with ionophore A23187, agents known to cause platelet ADP secretion. By comparison, FSBA did not inhibit binding of vWF induced by ristocetin, indicating that the ristocetin mechanism is not dependent on ADP. Human fibrinogen inhibited in a competitive manner the ADP-induced binding of 125I-labeled vWF (9 micrograms/ml) with an IC50 of 25 micrograms/ml. Conversely, unlabeled vWF inhibited ADP-induced binding of 125I-labeled fibrinogen (60 micrograms/ml) with an IC50 of 16 micrograms/ml. A synthetic dodecapeptide (Mr, 1188), analogous with the specific platelet receptor recognition site of human fibrinogen gamma chain (gamma 400-411), inhibited binding of both 125I-labeled vWF and 125I-labeled fibrinogen to ADP-treated platelets, whereas it was without effect on binding of 125I-labeled vWF to ristocetin-treated platelets. These data indicate that vWF and fibrinogen have a common receptor mechanism for their interaction with human platelets that is dependent on ADP occupancy of its binding sites and is recognized by the sequence of 12 amino acid residues at the carboxyl terminus of the human fibrinogen gamma chain.

Platelet impedance aggregation in whole blood and its inhibition by antiplatelet drugs

Platelet aggregation was studied in citrated whole blood by an electrical impedance method. Blood samples from normal volunteers were studied with the aim of finding a suitable method for the routine study of samples from patients. An erratic tracing and low maximum aggregation were seen in samples with a high normal haematocrit. Optimal aggregation was seen when blood was diluted to a haematocrit of .300; isotonic saline was a better diluent than platelet poor plasma. No appreciable differences were seen when the platelet count was diluted down to 50 X 10(9)/l, after which there was a progressive reduction in response. Dose response curves were obtained, and normal ranges for ADP, collagen, and sodium arachidonate were determined. Acetylsalicylic acid had a more pronounced effect on ADP aggregation than on collagen. Prostacyclin (Epoprostenol) and the synthetic prostacyclin analogue ZK 36,374 both showed dose dependent inhibition of aggregation, but the duration of effect of the latter was much longer (greater than 6 h).