Correction of the platelet adhesion defect in delta-storage pool deficiency at elevated hematocrit--possible role of adenosine diphosphate

Previous studies on patients with storage pool deficiency (SPD) who are specifically deficient in platelet dense granules (delta-SPD) have suggested a role for dense granule substances, in all likelihood adenosine diphosphate (ADP), in mediating thrombus formation on subendothelium at high shear rates. The role of dense granule substances in mediating platelet adhesion appears to be more complicated Previous studies in delta-SPD suggested an adhesion defect that was strongly influenced by the patient's hematocrit (Hct) value. To explore further the possibility that red blood cells (RBCs) may influence the role that platelet storage granules play in mediating adhesion at high shear rates, we have measured adhesion (and thrombus formation) throughout a preselected range of Hct values (30% to 60%) in normal subjects and in patients with delta-SPD. The present studies confirm the defect in platelet adhesion in patients with delta-SPD, most significantly at Hct values of 30% to 40%. This defect (but not that of thrombus formation) can be completely corrected by the addition of RBCs. The correction of the platelet adhesion defect by RBCs was specific for delta-SPD; it was not observed in either von Willebrand's disease or thrombasthenia. Studies performed on normal blood under conditions that could be expected to block any effect of ADP on adhesion and an analysis of the type of adhesion defect in delta-SPD suggest that ADP may be involved in the process required for platelet spreading on the subendothelium. The corrective effect of RBCs on platelet adhesion in delta-SPD appears to be chemical rather than physical in nature, possibly due to shear-induced release of RBC ADP or to other recently described properties of RBCs that enhance collagen-induced platelet interactions.

Protein-tyrosine phosphorylation and p72syk activation in human platelets stimulated with collagen is dependent upon glycoprotein Ia/IIa and actin polymerization

In human platelets treated with acetylsalicylic acid, collagen induced protein-tyrosine-phosphorylation of several proteins. The major 75 kDa band included cortactin and auto-phosphorylated p72syk. p72syk activity rapidly increased upon collagen stimulation, whereas p60c-src activation was below detectable levels. A combination of inhibitors to remove the effects of extracellular and intracellular Ca2+, released ADP, and fibrinogen binding to GPIIb/IIIa delayed and attenuated the major 75 kDa band. By contrast, p72syk activation was not inhibited by these treatments. Cytochalasin D completely inhibited protein tyrosine phosphorylation and p72syk activation. It also potently inhibited aggregation and [Ca2+]i elevation. Anti-GPIa/IIa MoAb in a concentration-dependent manner partially attenuated protein tyrosine phosphorylation and p72syk activation. Its inhibitory effects on intracellular Ca2+ mobilization, release of intracellular granule contents, and aggregation also were partial. No tyrosine kinase activity was coprecipitated with GPIa/IIa. These results suggest that p72syk activation lies upstream of protein tyrosine phosphorylation, Ca2+ mobilization, ADP release, thromboxane A2 production and aggregation. GPIa/IIa plays a key role in p72syk activation induced by collagen, but other collagen receptors may work in synergy to fully activate p72syk. Actin polymerization is a prerequisite for both p72syk activation and other intracellular signal transduction pathways.

Fosinopril reduces ADP-induced platelet aggregation in hypertensive patients

Platelets are intimately involved in atherosclerosis, and hypertension is a known risk factor for coronary artery disease. The angiotensin-converting enzyme (ACE) inhibitors were demonstrated to reduce hypertension and attenuate atherosclerosis. Because increased platelet aggregation was shown in hypertensive patients, the effect of a new ACE inhibitor, fosinopril, on platelet aggregation was studied. Fosinopril therapy (10 mg/day for 4 weeks) in 18 male hypertensive patients showed > or = 31% reduction in ADP-induced platelet aggregation. In vitro studies showed that fosinopril had similar inhibitory effect on ADP-induced platelet aggregation. No inhibitory effect could be detected with collagen as the aggregating agent. Finally, inhibition of platelet aggregation by fosinopril was less effective in platelets derived from hypertensive patients as compared with platelets derived from normal subjects. We conclude that fosinopril possesses a significant inhibitory activity on ADP-induced platelet aggregation both in vitro and in vivo.

Disposition of diadenosine 5',5"'-P1,P4-tetraphosphate (Ap4A) in rats

The disposition of diadenosine 5'5"'-P1,P4-tetraphosphate (Ap4A), an endogenous dinucleotide, was investigated in rats. The degradation of Ap4A in rat plasma was very rapid and could be explained by a Michaelis-Menten equation: Km and Vmax values were 1.69 micrograms/ml and 4.32 micrograms/min/ml, respectively. Ap4A was degraded in rat plasma to ATP and AMP, but not to 2 ADP molecules, and these nucleotides were further degraded through adenosine. The degradations kinetics were examined. After intravenous bolus injection, Ap4A in plasma declined rapidly and the rate of elimination was dose-dependent: the biological half-life was about 3s at the dose of 1 mg/kg and was longer at 3 mg/kg. When Ap4A was administered by intravenous infusion (0.5 or 1.0 mg/kg/min), the plasma level rapidly reached a steady-state, which then rapidly declined after stopping the infusion.

[Concentration of adenine nucleotides in blood of predialysis patients with chronic renal failure]

Intraerythrocyte and blood level ATP concentration is increased in CRF. But little is known on the blood concentration of ADP and AMP in CRF. HPLC was applied to evaluate the ATP, ADP, AMP concentration in blood of 25 CRF patients, with serum creatinine from 2.4 mg/dl to 14.4 mg/dl treated conservatively. Controls were healthy people, with normal renal function. In CRF ATP was higher (p < 0.001) and ADP, AMP and hypoxanthine were lower (p < 0.001) then in controls. Also ATP correlated (r = 0.78; p < 0.001) with serum phosphate and (r = 0.40; p < 0.05) with serum creatinine in CRF patients. Adenine nucleotides turnover is increased in CRF and this process is related to severity of the disease.

Time dependence of accumulation and binding of inorganic and organic arsenic species in rabbit erythrocytes

The uptake by rabbit erythrocytes of 0.4 mM arsenate, As(V), monomethylarsinate, MMA(V) and dimethylarsonate, DMA(V) were compared over 24 h. In membrane-free hemolysate, the distribution of As between proteins (10 kDa) and ultrafiltrate was determined by ultrafiltration and arsenic species in the ultrafiltrate were identified by thin layer chromatography methods. 1H spin-echo Fourier transform NMR was used to follow the binding of these arsenic species to glutathione (GSH). 31P-NMR was used to observe their effects on high-energy adenine nucleotide levels (ATP, ADP). These results demonstrate that As(III) readily accumulates in cells, reaches a quasi-plateau at 78% of the total As in the incubation after 1 h and 88% of the total As after 24 h. On average, 20% of the total erythrocyte As(III) burden is associated with the protein fraction, particularly with hemoglobin (Hb). About 68% of the erythrocyte As(III) burden is bound to GSH. As(III) has no effect on ATP levels during a 5-h incubation. By comparison, As(V) enters erythrocytes more slowly (53% of the total As after 5 h). Erythrocytes take up 81% of the As(V) in the reaction system after a 24 h incubation. Of the total As burden in As(V)-exposed erythrocytes, 22% was associated with the proteins (10 kDa) and possibly reduced to As(III) and 59% was in the ultrafiltrate (8% as As(III) and 51% as As(V)). This finding indicates that, over a 24 h incubation period, the reduction of As(V) to As(III) may account for 30% of the total As in rabbit erythrocytes. As(V) present in the erythrocytes enters the phosphate pool and depletes ATP. In comparison, about 65% of the total MMA(V) or about 44% of the total DMA(V) in the incubation system is taken up by rabbit erythrocytes during a 24 h incubation. Neither organoAs species perturbed the Hb signals observed by spin-echo Fourier transform NMR and the binding to GSH was minimal. Unlike As(V), MMA(V) and DMA(V) do not perturb phosphate metabolism, showing that, despite their pentavalent oxidation state, these arsenic species are not analogs for phosphate.

Physical and chemical effects of red cells in the shear-induced aggregation of human platelets

Both chemical and physical effects of red cells have been implicated in the spontaneous aggregation of platelets in sheared whole blood (WB). To determine whether the chemical effect is due to ADP leaking from the red cells, a previously described technique for measuring the concentration and size of single platelets and aggregates was used to study the shear-induced aggregation of platelets in WB flowing through 1.19-mm-diameter polyethylene tubing in the presence and absence of the ADP scavenger enzyme system phosphocreatine-creatine phosphokinase (CP-CPK). Significant spontaneous aggregation was observed at mean tube shear rates, (G) = 41.9 and 335 s-1 (42% and 13% decrease in single platelets after a mean transit time (t) = 43 s, compared to 89 and 95% decrease with 0.2 microM ADP). The addition of CP-CPK, either at the time of, or 30 min before each run, completely abolished aggregation. In the presence of 0.2 microM ADP, CP-CPK caused a reversal of aggregation at (t) = 17 s after 30% of single cells had aggregated. To determine whether red cells exert a physical effect by increasing the time of interaction of two colliding platelets (thereby increasing the proportion of collisions resulting in the formation of aggregates), an optically transparent suspension of 40% reconstituted red cell ghosts in serum containing 2.5-micron-diameter latex spheres (3 x 10(5)/microliters) flowing through 100-microns-diameter tubes was used as a model of platelets in blood, and the results were compared with those obtained in a control suspension of latex spheres in serum alone. Two-body collisions between microspheres in the interior of the flowing ghost cell or serum suspensions at shear rates from 5 to 90 s-1 were recorded on cine film. The films were subsequently analyzed, and the measured doublet lifetime, tau meas, was compared with that predicted by theory in the absence of interactions with other particles, tau theor. The mean (tau meas/tau theor) for doublets in ghost cell suspensions was 1.614 +/- 1.795 (SD; n = 320), compared to a value of 1.001 +/- 0.312 (n = 90) for doublets in serum. Whereas 11% of doublets in ghost cell suspensions had lifetimes from 2.5 to 5 times greater than predicted, in serum, no doublets had lifetimes greater than 1.91 times that predicted. There was no statistically significant correlation between tau meas/tau theor and shear rate, but the values of tau meas/tau theor for low-angle collisions in ghost cell suspensions were significantly greater than for high-angle collisions.

Alzheimer amyloid beta-peptides exhibit ionophore-like properties in human erythrocytes

There is growing evidence that the amyloid beta-peptide (beta 1-40) is involved in the aetiology of Alzheimer's disease also implicating an altered calcium homeostasis of affected cells. Beta 1-40 has been proposed to form calcium channels in synthetic bilayer membranes [1]. We wanted to investigate in the present study whether beta 1-40 (or fragments thereof) could act as ionophores in a biological membrane like the one in human erythrocytes. Incubation of the cells for 2 h and 4 h at 37 degrees C together with 6 mumol L-1 of beta 1-40 or of fragments beta 1-28 and beta 25-35, resulted in a significantly decreased energy charge qualitatively similar to the one obtained by a known calcium ionophore (A 23187, 0.05 mumol L-1). Moreover, beta 1-40 and its two fragments induced a significant alteration of 45Ca permeability in human red blood cells of the same type as the one achieved by the calcium ionophore. The ionophoric action of beta 1-40 and its two fragments may lead to an increase of the intracellular calcium ion concentration, in turn resulting in enhanced Ca(2+)-ATPase activity and a decrease in energy charge. This may be valid also for neuronal plasma membranes and could, therefore, be a possible aetiological mechanism in Alzheimer's disease.

Effects of submaximal physical exercise and immobilization in bed on the adenine nucleotides concentration in human blood platelets

The effects of submaximal physical exercise (75% VO2max) and one month immobilization in bed on the adenine nucleotides concentration in human blood platelets were studied and compared. We have shown that after submaximal exercise and after immobilization in bed the concentrations of adenine nucleotides in blood platelets mainly ATP and ADP were decreased and probably caused by the stimulation of platelet secretory process. Thrombin which stimulated the release of 58.2% +/- 1.5% of total adenine nucleotides from control platelets, liberated decreased amounts of nucleotides from platelets after physical exercise and after immobilization in bed (39.9 +/- 2.1% and 23.6 +/- 2.03% of total, respectively).

Oculocutaneous albinism and bruising in two sisters--probable Hermansky-Pudlak syndrome

Cases of Hermansky-Pudlak syndrome may present to the dermatologist, ophthalmologist or haematologist. Classically the diagnosis rests on the triad of oculocutaneous albinism, a bruising tendency and the presence of characteristic pigmented-containing cells in the bone marrow. Specific tests of platelet function can, however, suggest the diagnosis without recourse to invasive techniques. We describe the disease in two young sisters.

Further characterization of the inhibition of platelet aggregation by a plasma factor(s) in unmedicated unipolar depressed patients

To investigate further the inhibition of platelet aggregation by a plasma factor(s) in unipolar depression, a series of assays were performed in which the platelet-rich plasma of a male volunteer was preincubated with the plasma of either unmedicated unipolar depressed patients or age-matched controls. Platelet aggregation was initiated by the following aggregating agents; ADP (10 and 2.5 microM), ADP/5HT (0.5 microM ADP + 50 microM 5HT and 0.5 microM ADP + 25 microM 5HT) and adrenaline (10 and 1 microM) (that act on different platelet membrane receptors) and by the following agents; sodium fluoride (20 mM), calcium ionophore A23,187 (19 microM) and phorbol-12-myristate-13-acetate (3.24 microM) (that act at specific intracellular sites). The plasma of depressed patients significantly reduced the platelet aggregatory response for each of the aggregating agents at each of the concentrations tested. Therefore, it is concluded that the inhibition of platelet aggregation by a plasma factor(s) may be irreversible in nature and may have an intracellular site(s) of action, possibly at, or beyond, the site of activated protein kinase C.

Surface and bulk effects on platelet adhesion and aggregation during simple (laminar) shear flow of whole blood

This study attempts to clarify the role of the artificial surface and the fluid bulk on platelet adhesion and aggregation events during simple shear flow of whole blood. The experimental approach involved the shearing of fresh whole blood samples over the shear rate range of 720-5680 s-1, which corresponded to a shear stress maximum of about 150 dyn cm-2. Results on platelet adhesion, measured as surface coverage by platelets, and platelet aggregation, measured in terms of reduction in platelet count and adenosine diphosphate (ADP) release, were determined as a function of the surface to volume ratio (S/V); and artificial surface used. Both shear-induced platelet adhesion and platelet count reduction showed significant variation over the range of S/V employed. The ratios between the three different S/V values used in this system (10:6:4) were about the same as the ratio of the shear rate-averaged results obtained. Also, for shear-induced hemolysis, an increase in the release of hemoglobin from red blood cells was found as S/V was increased, again with ratios between the shear rate-averaged values similar to the ratio of S/V values employed. The shear-induced release of ADP, presumably from platelets and from red blood cells indicated a different dependence of ADP release on S/V than was observed for the other parameters reported. Irreversible platelet aggregation was expected to occur because the amount of ADP that was released as a result of the shear was substantial. Models proposed to explain the experimental results were found to support a surface-controlled mechanism.

Increase in plasma levels of adenosine and adenine nucleotides after intravenous infusion of buflomedil in humans

To clarify the mode of action of the vasoactive agent buflomedil, we evaluated plasma levels of adenosine and adenine nucleotides after intravenous (i.v.) infusion in humans of 50, 100, and 200 mg of the drug in 20 min. Buflomedil induced an increase of the same order of magnitude in plasma levels of adenosine and adenine nucleotides. Maximal adenosine increase (84%) was observed at the end of the infusion period, whereas peak plasma levels of ATP and ADP (69 and 55%, respectively) and of AMP (61%) were detected 10 and 5 min after discontinuation of infusion, respectively. Although the exact mode of action of buflomedil at the molecular level remains unclear, some indirect findings suggest that the increase in adenosine may be due to enhanced release rather than to inhibition of cell uptake. Because such activity of buflomedil consists of enhancement of physiologic mechanisms of vasodilation and tissue protection occurring in the course of ischemic events, new pharmacologic perspectives for the drug may arise.

Effect of muscular exercise by bicycle ergometer on erythrocyte purine nucleotides

The effect of muscular exercise by bicycle ergometer on erythrocyte purine nucleotides was investigated in 6 athletes. Muscular exercise increased the concentration of inosine monophosphate from 5.9 +/- 1.1 to 7.3 +/- 1.3 nmol/ml in venous erythrocytes and from 5.7 +/- 1.0 to 6.8 +/- 1.4 nmol/ml in arterial erythrocytes, respectively, while it decreased the concentrations of adenosine diphosphate and adenosine monophosphate from 189.3 +/- 42.7 to 141.2 +/- 26.9 and from 26.0 +/- 7.8 to 15.7 +/- 4.3 nmol/ml in venous erythrocytes and also decreased their concentrations from 195.1 +/- 51.0 to 141 +/- 29.2 and from 26.5 +/- 9.6 to 14.8 +/- 3.0 nmol/ml in arterial erythrocytes, respectively. The muscular exercise also increased the concentration of inorganic phosphate in venous plasma from 1.12 +/- 0.12 to 1.46 +/- 0.22 mmol/l, that of NH3 in blood from 41.90 +/- 6.91 to 150.22 +/- 50.80 mumol/l, that of lactic acid in blood from 7.90 +/- 1.71 to 61.03 +/- 18.43 mg/dl and that of hypoxanthine in venous plasma from 1.32 +/- 0.36 to 18.14 +/- 4.87 mumol/l, respectively. Therefore, in vitro study was performed to investigate whether inorganic phosphate, NH4Cl, lactic acid or hypoxanthine affects nucleotides in erythrocytes. After 2 hour-incubation, 2 mM inorganic phosphate increased the erythrocyte concentration of inosine monophosphate 1.6 fold but decreased the erythrocyte concentrations of adenosine monophosphate and adenosine diphosphate 0.72 and 0.89 fold, respectively, in the suspension (pH 7.35), as compared with 1 mM inorganic phosphate. However NH4Cl, lactic acid or hypoxanthine did not affect erythrocyte purine nucleotides.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of heparin and protamine sulfate on platelet ADP and platelet factor 4 release and the expression of glycoprotein IIb/IIIa

We present results concerning the pathogenic mechanism of heparin-induced thrombocytopenia type I. An ELISA was developed for directly measuring the expression of glycoprotein IIb/IIIa (GPIIb/IIIa) on platelets in the presence and absence of ADP and under the influence of various heparins. In addition, the release of ADP and platelet factor 4 (PF4) was measured in platelet-rich plasma. Heparin also induced the expression of GPIIb/IIIa without prior stimulation with ADP. On the other hand we could demonstrate that the addition of heparins and protamine sulfate to platelets resulted in a significant release of intracellularly stored ADP and PF4. These results suggested that heparin(oid)s modulate the expression of GPIIb/IIIa with ADP as a mediator, and that protamine sulfate is contraindicated as an antidote in heparin-induced thrombocytopenia.

Comparative aspects of Na(+)-K+ and Ca(2+)-Mg2+ ATPase in erythrocyte membranes of various mammals

This work is a comparative study of Na(+)-K+ and Ca(2+)-Mg2+ ATPase associated with the erythrocyte plasma membranes in different mammals. The method used to test the activity of these enzymes is based on quantitative measurements of ADP released during the reaction with HPLC: the chromatographic type is an Ion-Pair Reversed Phase. We have found that the levels of Ca2+ stimulated ATPase are higher than those of Na(+)-K+ ATPase in red blood cells of all the different mammalian species, with the only exception being lamb erythrocytes where the values of both the ATPase activities are almost equal. The results obtained have shown different levels of the Na(+)-K+ ATPase as well as of the Ca2+ stimulated ATPase activity. Furthermore, we have made a comparative study of the ATPase activities in different red blood cells with specific reference to the optimum pH, thermostability, kinetic characteristics and the inhibitory effects of ouabain and vanadate.

Platelet pertussis toxin-sensitive G proteins in affective disorders

Pertussis toxin (islet-activating protein, IAP) sensitive guanine nucleotide-binding regulatory (G) proteins were quantitatively determined using [32P]ADP-ribosylating response in the platelet membranes prepared from patients with affective disorders (3 bipolar, 10 major depression) and sex- and age-matched controls. IAP-catalyzed [32P]ADP-ribosylation was not significantly different between patients and controls, suggesting that the quantity of IAP-sensitive G proteins is unaltered in affective disorder patients. The implication of this result was discussed with special reference to the previous reports dealing with the role of G proteins in affective disorders.

Phosphate from the phosphointermediate (EP) of the human red blood cell Na/K pump is coeffluxed with Na, in the absence of external K

This study is concerned with Na/K pump-mediated phosphate efflux that occurs during uncoupled Na efflux in human red blood cells. Uncoupled Na efflux is known to be a ouabain-sensitive mode of the Na/K pump that occurs in the absence of external Nao and Ko. Because this efflux (measured with 22Na) is also inhibited by 5 mM Nao, the efflux can be separated into a Nao-sensitive and a Nao-insensitive component. Previous work established that the Nao-sensitive efflux is actually comprised of an electroneutral coefflux of Na with cellular anions, such as SO4 (as 35SO4). The present work focuses on the Nao-insensitive component in which the principal finding is that orthophosphate (P(i)) is coeffluxed with Na in a ouabain-sensitive manner. This P(i) efflux can be seen to occur, in the absence of Ko, in both DIDS-treated intact cells and resealed red cell ghosts. This efflux of P(i) was shown to be derived directly from the pump's substrate, ATP, by the use of resealed ghosts made to contain both ATP and P(i) in which either the ATP or the P(i) were labeled with, respectively, [gamma-32P]ATP or [32P]H3PO4. (These resealed ghosts also contained Na, Mg, P(i), SO4, Ap5A, as well as an arginine kinase/creatine kinase nucleotide regenerating system for the control of ATP and ADP concentrations, and were suspended usually in (NMG)2SO4 at pH 7.4.) It was found that 32P was only coeffluxed with Na when the 32P was contained in [gamma-32P]ATP and not in [32P]H3PO4. This result implies that the 32P that is released comes from ATP via the pump's phosphointermediate (EP) without commingling with the cellular pool of P(i). Ko (as K2SO4) inhibits this 32P efflux as well as the Nao-sensitive 35SO4 efflux, with a K0.5 of 0.3-0.4 mM. The K0.5 for inhibition of P(i) efflux by Ko is not influenced by Nao, nor can Nao act as a congenor for Ko in any of the flux reactions involving Ko. The stoichiometry of Na to SO4 and Na to P(i) efflux is approximately 2:1 under circumstances where the stoichiometry of Na effluxed to ATP utilized is 3:1. From these and other results reported, it is suggested that there are two types of uncoupled Na efflux that differ from each other on the basis of their sensitivity to Nao, the source (cellular vs substrate) and kind of anion (SO4 vs P(i)) transported.(ABSTRACT TRUNCATED AT 400 WORDS)

ADP+orthophosphate (P(i)) stimulates an Na/K pump-mediated coefflux of P(i) and Na in human red blood cell ghosts

The Na/K pump in human red blood cells that normally exchanges 3 Nai for 2 Ko is known to continue to transport Na in a ouabain-sensitive and ATP-dependent manner when the medium is made free of both Nao and Ko. Although this Na efflux is called "uncoupled" because of removal of ions to exchange with, the efflux has been shown to be comprised of a coefflux with cellular anions. The work described in this paper presents a new mode of operation of uncoupled Na efflux. This new mode not only depends upon the combined presence of ADP and intracellular orthophosphate (P(i))i but the Na efflux that is stimulated to occur is coeffluxed with (P(i))i. These studies were carried out with DIDS-treated resealed red cell ghosts, suspended in buffered (NMG)2SO4, that were made to contain, in addition to other constituents, varying concentrations of ADP and P(i) together with Na2 SO4, MgSO4 and hexokinase. While neither ADP nor P(i) was effective alone, ouabain-sensitive uncoupled Na efflux, (measured with 22Na) could be activated by [ADP+P(i)] where the K0.5 for ADP in the presence of 10 mmol (P(i))i/liter ghosts was 100-200 mumol/liter ghosts and the K0.5 for (P(i))i, in the presence of 500 mumol ADP/liter ghosts was 3-4 mmol/liter ghosts. [ADP+P(i)] activation of this Na efflux could be inhibited by as little as 2 mumol ATP/liter ghosts but the inhibition could be relieved by the addition of 50 mM glucose, given entrapped hexokinase. While ouabain-sensitive Na efflux was found to be coeffluxed with P(i) (measured with entrapped [32P]H3PO4), this was not so for SO4 (measured with 35SO4). The stoichiometry of Na to P(i) efflux was found to be approximately 2 to 1. Na efflux as well as (P(i))i efflux were both inhibited by 10 mM Nao (K0.5 approximately equal to 4 mM). But, whereas 20 mM Ko (K0.5 approximately equal to 6 mM) inhibited the efflux of (P(i))i, as would be expected from previous work, Na efflux was actually increased. When Ko influx was measured in this situation there was a 1 for 1 exchange of Nai for Ko, that is, of course, downhill with respect to the gradient of each ion. Surprisingly AsO4 was unable to replace P(i) for activation of Na efflux but Na efflux could be inhibited by vanadate and oligomycin. In terms of mechanism, it is likely that ADP acts to promote the formation of the phosphoenzyme (EP) by (P(i))i that would otherwise be inhibited by Nai.(ABSTRACT TRUNCATED AT 400 WORDS)

Mechanisms of acid-base homeostasis in acetate and bicarbonate dialysis, lactate hemofiltration and hemodiafiltration

The different mechanisms of acidosis buffering were investigated in 15 RDT patients dialyzed in cross-over with four depurative techniques: acetate dialysis (AD), bicarbonate dialysis (BD), lactate hemofiltration (LHF) and hemodiafiltration (HDF) with acetate bath and lactate reinfusion fluid. Blood pH, bicarbonate, blood gases, intraerythrocytic pH - on red cell hemolisates - anion gap, L-lactate, pyruvate, adenosinmonophosphate (ADP) and 2-3 Diphosphoglycerate (2-3 DPG) levels were evaluated. During AD the intradialytic buffering is initially achieved by the CO2 fall and later by the acetate metabolism and an important bicarbonate shift from the intra to the extracellular space. A physiological compensation is obtained during BD with bicarbonate administration and a mild ventilatory response to the pCO2 increase. In LHF the massive lactate administration, with plasma levels of 7 mmol/l, strongly alters the Central Nervous System elettroneutrality inducing a hyperventilatory response with a purely pulmonary acidosis buffering. Furthermore the lactate/pyruvate ratio rose as high as 40:1 with ADP increase and cellular energy depletion. In HDF several different mechanisms are associated: the CO2 fixation, the acetate muscular metabolism, the intra-extracellular bicarbonate shift with the pulmonary response driven by lactate Central Nervous System penetration.

Binding of [3H]-2-methylthio ADP to rat platelets--effect of clopidogrel and ticlopidine

Thienopyridine compounds, including ticlopidine and clopidogrel, have been found to selectively inhibit adenosine 5' diphosphate (ADP)-induced platelet aggregation and adenylyl cyclase ex vivo, but the mechanism of their antiplatelet action remains to be determined. This study was aimed at investigating the effect of clopidogrel and ticlopidine on the binding of [3H]-2-methylthio- adenosine-5'-diphosphate (2-MeS-ADP) to rat platelets. Binding of [3H]-2-MeS-ADP to rat platelets was time-dependent and saturable. Scatchard analysis of the saturation binding data indicated that [3H]-2-MeS-ADP bound to one population of specific binding sites with high affinity (KD = 0.78 +/- 0.05 nM; Bmax = 156.3 +/- 4.8 fmole/10(8) cells) (n = 3). Unlabeled 2-MeS-ADP and ADP competitively and selectively inhibited the specific binding of [3H]-2-MeS-ADP with IC50 values of 11.3 +/- 1.2 nM and 11.3 +/- 0.7 microM, respectively (n = 3). Other nucleotide analogs such as ADP-beta S, ATP and ATP-alpha S also antagonized [3H]-2-MeS-ADP binding. When administered orally at doses ranging from 1 to 25 mg/kg, clopidogrel inhibited ADP- or 2-MeS-ADP-induced platelet aggregation as well as ADP or 2-MeS-ADP-induced inhibition of intraplatelet adenylyl cyclase. When measured in parallel, clopidogrel reduced in a dose-dependent manner the binding of [3H]-2-MeS-ADP to rat platelets ex vivo. Clopidogrel administration resulted in the decrease of [3H]-2-MeS-ADP binding sites on platelets without any significant change in the affinity; this indicates noncompetitive binding. Ticlopidine (200 mg/kg a day for 3 days) behaved in the same way.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of minor surgery on some aspects of platelet function

Blood from 33 patients undergoing elective surgery for non-malignant disorders was examined before operation and on the third post-operative day. The following parameters were measured: (a) total platelet count (b) platelet volume (c) released adenine nucleotides (ATP and ADP). Whole blood platelet count (WBPC) levels increased significantly after surgery and there was significant correlations between its pre- and post-operative values (r = 0.616, p < 0.05). The relationship between mean arithmetic volume after operation (MAVA) and the whole blood platelet count after operation (WBPC A) was negative and significant (r = -0.425, p < 0.05). The results also revealed no significant differences between total and released nucleotides before and after surgery. The significant increase in whole blood platelet count post operatively may have been due to release of the splenic platelet stores. Platelets in the spleen are said to be old platelets hence the lack of a significant change in platelet volume may be due to sampling taking place three days after surgery which may not have corresponded to the time of the optimum production of young larger platelets. Also, the trauma of minor surgery may not have been strong enough to stimulate platelet production in the marrow. In the light of the above findings further investigations may be conducted in which post-operative samples would be collected at varying intervals to determine whether post-operative changes in platelet volume occur at all and when.