Hippocampal LTP and contextual learning require surface diffusion of AMPA receptors.

Long-term potentiation (LTP) of excitatory synaptic transmission has long been considered a cellular correlate for learning and memory. Early LTP (less than 1 h) had initially been explained either by presynaptic increases in glutamate release or by direct modification of postsynaptic AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor function. Compelling models have more recently proposed that synaptic potentiation can occur by the recruitment of additional postsynaptic AMPA receptors (AMPARs), sourced either from an intracellular reserve pool by exocytosis or from nearby extra-synaptic receptors pre-existing on the neuronal surface. However, the exact mechanism through which synapses can rapidly recruit new AMPARs during early LTP remains unknown. In particular, direct evidence for a pivotal role of AMPAR surface diffusion as a trafficking mechanism in synaptic plasticity is still lacking. Here, using AMPAR immobilization approaches, we show that interfering with AMPAR surface diffusion markedly impairs synaptic potentiation of Schaffer collaterals and commissural inputs to the CA1 area of the mouse hippocampus in cultured slices, acute slices and in vivo. Our data also identify distinct contributions of various AMPAR trafficking routes to the temporal profile of synaptic potentiation. In addition, AMPAR immobilization in vivo in the dorsal hippocampus inhibited fear conditioning, indicating that AMPAR diffusion is important for the early phase of contextual learning. Therefore, our results provide a direct demonstration that the recruitment of new receptors to synapses by surface diffusion is a critical mechanism for the expression of LTP and hippocampal learning. Since AMPAR surface diffusion is dictated by weak Brownian forces that are readily perturbed by protein-protein interactions, we anticipate that this fundamental trafficking mechanism will be a key target for modulating synaptic potentiation and learning.

Regulation of AMPA receptor surface trafficking and synaptic plasticity by a cognitive enhancer and antidepressant molecule.

The plasticity of excitatory synapses is an essential brain process involved in cognitive functions, and dysfunctions of such adaptations have been linked to psychiatric disorders such as depression. Although the intracellular cascades that are altered in models of depression and stress-related disorders have been under considerable scrutiny, the molecular interplay between antidepressants and glutamatergic signaling remains elusive. Using a combination of electrophysiological and single nanoparticle tracking approaches, we here report that the cognitive enhancer and antidepressant tianeptine (S 1574, [3-chloro-6-methyl-5,5-dioxo-6,11-dihydro-(c,f)-dibenzo-(1,2-thiazepine)-11-yl) amino]-7 heptanoic acid, sodium salt) favors synaptic plasticity in hippocampal neurons both under basal conditions and after acute stress. Strikingly, tianeptine rapidly reduces the surface diffusion of AMPA receptor (AMPAR) through a Ca(2+)/calmodulin-dependent protein kinase II (CaMKII)-dependent mechanism that enhances the binding of AMPAR auxiliary subunit stargazin with PSD-95. This prevents corticosterone-induced AMPAR surface dispersal and restores long-term potentiation of acutely stressed mice. Collectively, these data provide the first evidence that a therapeutically used drug targets the surface diffusion of AMPAR through a CaMKII-stargazin-PSD-95 pathway, to promote long-term synaptic plasticity.

Wavelet analysis for single molecule localization microscopy.

Localization of single molecules in microscopy images is a key step in quantitative single particle data analysis. Among them, single molecule based super-resolution optical microscopy techniques require high localization accuracy as well as computation of large data sets in the order of 10(5) single molecule detections to reconstruct a single image. We hereby present an algorithm based on image wavelet segmentation and single particle centroid determination, and compare its performance with the commonly used gaussian fitting of the point spread function. We performed realistic simulations at different signal-to-noise ratios and particle densities and show that the calculation time using the wavelet approach can be more than one order of magnitude faster than that of gaussian fitting without a significant degradation of the localization accuracy, from 1 nm to 4 nm in our range of study. We propose a simulation-based estimate of the resolution of an experimental single molecule acquisition.

Surface trafficking of N-methyl-D-aspartate receptors: physiological and pathological perspectives.

The N-methyl-D-aspartate receptor (NMDAR) plays a crucial role in shaping the strength of synaptic connections. Over the last decades, extensive studies have defined the cellular and molecular mechanisms by which synaptic NMDARs control the maturation and plasticity of synaptic transmission, and how altered synaptic NMDAR signaling is implicated in neurodegenerative and psychiatric disorders. It is now clear that activation of synaptic or extrasynaptic NMDARs produces different signaling cascades and thus neuronal functions. Our current understanding of NMDAR surface distribution and trafficking is only emerging. Exchange of NMDARs between synaptic and extrasynaptic areas through surface diffusion is a highly dynamic and regulated process. The aim of this review is to describe the identified mechanisms that regulate surface NMDAR behaviors and discuss the impact of this new trafficking pathway on the well-established NMDAR-dependent physiological and pathophysiological processes.

Cross-linking of IgG receptors inhibits membrane immunoglobulin-stimulated calcium influx in B lymphocytes.

By cross-linking membrane immunoglobulins (mIg), the antigenic stimulation of B lymphocytes induces an increase in intracellular free calcium levels ([Ca2+]i) because of a combination of release from intracellular stores and transmembrane influx. It has been suggested that both events are linked, as in a number of other cases of receptor-induced increase in [Ca2+]i. Conversely, in B lymphocytes, type II receptors for the Fc fragment of IgG (Fc gamma RII) inhibit mIg-mediated signaling. Thus, we have investigated at the level of single cells if these receptors could act on specific phases of mIg Ca2+ signaling. Lipopolysaccharide-activated murine B splenocytes and B lymphoma cells transfected with intact or truncated Fc gamma RII-cDNA were used to determine the domains of Fc gamma RII implicated in the inhibition of the Ca2+ signal. [Ca2+]i was measured in single fura-2-loaded cells by microfluorometry. The phases of release from intracellular stores and of transmembrane influx were discriminated by using manganese, which quenches fura-2, in the external medium as a tracer for bivalent cation entry. The role of membrane potential was studied by recording [Ca2+]i in cells voltage-clamped using the perforated patch-clamp method. Cross-linking of mIgM or mIgG with F(ab')2 fragments of anti-Ig antibodies induced a sustained rise in [Ca2+]i due to an extremely fast and transitory release of Ca2+ from intracellular stores and a long lasting transmembrane Ca2+ influx. The phase of influx, but not that of release, was inhibited by membrane depolarization. The increase in [Ca2+]i occurred after a delay inversely related to the dose of ligand. Co-cross-linking mIgs and Fc gamma RII with intact anti-Ig antibodies only triggered transitory release of Ca2+ from intracellular stores but no Ca2+ influx, even when the cell was voltage-clamped at negative membrane potentials. These transitory Ca2+ rises had similar amplitudes and delays to those induced by cross-linking mIgs alone. Thus, our data show that Fc gamma RII does not mediate an overall inhibition of mIg signaling but specifically affects transmembrane Ca2+ influx without affecting the release of Ca2+ from intracellular stores. Furthermore, this inhibition is not mediated by cell depolarization. Thus, Fc gamma RII represents a tool to dissociate physiologically the phases of release and transmembrane influx of Ca2+ triggered through antigen receptors.

Cyclic AMP-modulated potassium channels in murine B cells and their precursors.

A voltage-dependent potassium current (the delayed rectifier) has been found in murine B cells and their precursors with the whole-cell patch-clamp technique. The type of channel involved in the generation of this current appears to be present throughout all stages of pre-B-cell differentiation, since it is detected in pre-B cell lines infected with Abelson murine leukemia virus; these cell lines represent various phases of B-cell development. Thus, the presence of this channel is not obviously correlated with B-cell differentiation. Although blocked by Co2+, the channel, or channels, does not appear to be activated by Ca2+ entry. It is, however, inactivated by high intracellular Ca2+ concentrations. In addition, elevation of intracellular adenosine 3', 5'-monophosphate induces at all potentials a rapid decrease in the peak potassium conductance and increased rates of activation and inactivation. Therefore, potassium channels can be physiologically modulated by second messengers in lymphocytes.

Cytoplasmic domain heterogeneity and functions of IgG Fc receptors in B lymphocytes.

B lymphocytes and macrophages express closely related immunoglobulin G (IgG) Fc receptors (Fc gamma RII) that differ only in the structures of their cytoplasmic domains. Because of cell type-specific alternative messenger RNA splicing, B-cell Fc gamma RII contains an insertion of 47 amino acids that participates in determining receptor function in these cells. Transfection of an Fc gamma RII-negative B-cell line with complementary DNA's encoding the two splice products and various receptor mutants indicated that the insertion was responsible for preventing both Fc gamma RII-mediated endocytosis and Fc gamma RII-mediated antigen presentation. The insertion was not required for Fc gamma RII to modulate surface immunoglobulin-triggered B-cell activation. Instead, regulation of activation involved a region of the cytoplasmic domain common to both the lymphocyte and macrophage receptor isoforms. In contrast, the insertion did contribute to the formation of caps in response to receptor cross-linking, consistent with suggestions that the lymphocyte but not macrophage form of the receptor can associate with the detergent-insoluble cytoskeleton.

Calcium influx through nicotinic receptor in rat central neurons: its relevance to cellular regulation.

The Ca2+ permeability of a nicotinic acetylcholine receptor (nAChR) in the rat CNS was determined using both current and fluorescence measurements on medial habenula neurons. The elementary slope conductance of the nAChR channel was 11 pS in pure external Ca2+ (100 mM) and 42 pS in standard solution. Ca2+ influx through nAChRs resulted in the rise of cytosolic Ca2+ concentration ([Ca2+]i) to the micromolar range. This increase was maximal under voltage conditions (below -50 mV) in which Ca2+ influx through voltage-activated channels was minimal. Ca2+ influx through nAChRs directly activated a Ca(2+)-dependent Cl- conductance. In addition, it caused a decrease in the GABAA response that outlasted the rise in [Ca2+]i. These results underscore the physiological significance of Ca2+ influx through nAChR channel in the CNS.

Fast and reversible trapping of surface glycine receptors by gephyrin.

Variations in receptor number at a given synapse are known to contribute to synaptic plasticity, but methods used to establish this idea usually do not allow for the determination of the dynamics of these phenomena. We used single-particle tracking to follow in real time, on the cell surface, movements of the glycine receptor (GlyR) with or without the GlyR stabilizing protein gephyrin. GlyR alternated within seconds between diffusive and confined states. In the absence of gephyrin, GlyR were mostly freely diffusing. Gephyrin induced long confinement periods spatially associated with submembranous clusters of gephyrin. However, even when most receptors were stabilized, they still frequently made transitions through the diffusive state. These data show that receptor number in a cluster results from a dynamic equilibrium between the pools of stabilized and freely mobile receptors. Modification of this equilibrium could be involved in regulation of the number of receptors at synapses.

Mechanism of 4-aminopyridine action on voltage-gated potassium channels in lymphocytes.

The mechanism by which 4-aminopyridine (4-AP) blocks the delayed rectifier type potassium (K+) channels present on lipopolysaccharide-activated murine B lymphocytes was investigated using whole-cell and single channel patch-clamp recordings. 4-AP (1 microM-5 mM) was superfused for 3-4 min before applying depolarizing pulses to activate the channel. During the first pulse after application of 4-AP above 50 microM, the current inactivated faster, as compared with the control, but its peak was only reduced at high concentrations of 4-AP (Kd = 3.1 mM). During subsequent pulses, the peak current was decreased (Kd = 120 microM), but the inactivation rate was slower than in the control, a feature that could be explained by a slow unblocking process. After washing out the drug, the current elicited by the first voltage step was still markedly reduced, as compared with the control one, and displayed very slow activation and inactivation kinetics; this suggests that the K+ channels move from a blocked to an unblocked state slowly during the depolarizing pulse. These results show that 4-AP blocks K+ channels in their open state and that the drug remains trapped in the channel once it is closed. On the basis of the analysis of the current kinetics during unblocking, we suggest that two pathways lead from the blocked to the unblocked states. Computer simulations were used to investigate the mechanism of action of 4-AP. The simulations suggest that 4-AP must bind to both an open and a nonconducting state of the channel. It is postulated that the latter is either the inactivated channel or a site on closed channels only accessible to the drug once the cell has been depolarized. Using inside- and outside-out patch recordings, we found that 4-AP only blocks channels from the intracellular side of the membrane and acts by reducing the mean burst time. 4-AP is a weak base (pK = 9), and thus exists in ionized or nonionized form. Since the Kd of channel block depends on both internal and external pH, we suggest that 4-AP crosses the membrane in its nonionized form and acts from inside the cell in its ionized form.

Ion channels and B cell mitogenesis.

Given the presence of ionic channels at the membrane of lymphocytes, we have analyzed the effect of various channels blockers on B lymphocytes activation. TEA and 4-AP, two K+ channels blockers, quinine, a blocker of Ca2(+)-activated K+ channels, nickel and verapamil, two Ca2+ channels blockers, all inhibited LPS-induced B cell proliferation. However, these drugs neither inhibited the induction of Ia and Fc gamma RII expression nor cell enlargement and early RNA synthesis, indicating that the entry of B lymphocytes into G1 phase was not affected. In contrast, both late RNA synthesis and the induction of the TfR, which occur while the cell progress through G1, were inhibited by these blockers. These data show that TEA, quinine and verapamil block B lymphocyte activation during the G1 phase, probably between G1A and G1B. To question whether these effects were due to the block of voltage-activated K+ channels, we compared the ability of TEA, quinine, verapamil, 4-AP and nickel to block proliferation and K+ channels. A striking correlation was found for all the drugs but less for 4-AP. Moreover, TMA, a TEA analog unable to block K+ currents, did not affect B cell proliferation. Taken together, our data suggests that functional voltage-gated K+ channels are required at a precise stage of the G1 phase of the B cell cycle.

Cell migration as a five-step cycle.

The migration of cells over substrata is a fundamental and critical function that requires the co-ordination of several cellular processes which operate in a cycle. At the level of the light microscope, the cycle can be divided into five steps: (1) extension of the leading edge; (2) adhesion to matrix contacts; (3) contraction of the cytoplasm; (4) release from contact sites; and (5) recycling of membrane receptors from the rear to the front of the cell. Each step is dependent upon one or more cyclical biochemical processes. The development of many in vitro and subcellular assays for the fundamental biochemical processes involved has increased our understanding of each cycle dramatically in the last several years to include a definition of many of the protein and enzymic components, the role of the position of extracellular-matrix receptors on the cell, and the contribution of physical force. The next generation of questions are directed at resolving the roles of the many individual proteins in each step of the cell migration process. In this chapter we will examine each of the migration steps and discuss the biochemical mechanisms that may underlie them.

Effects of aging on cardiorespiratory responses to brief and intense intermittent exercise in endurance-trained athletes.

The aim of this study was to investigate the effects of aging on athletes' cardiorespiratory responses to a brief intense intermittent effort, using the force-velocity test as an exercise model. Twelve young athletes (24.8 +/- 1.3 years) and twelve master athletes (65.1 +/- 1.2 years) with similar heights, body masses, and endurance training schedules participated in this study. They performed both a maximal graded exercise and the force-velocity tests. The force-velocity test consisted of the repetition of 6-second sprints against increasing braking forces with 5-minute recovery periods. None of the subjects presented abnormal electrocardiogram responses to the tests. During the force-velocity test, the heart rate magnitudes of response in all subjects were correlated to the corresponding sprint power output (p < .001), with higher values for the young athletes (p < .001). Both groups had similar systolic blood pressure peaks of response during the force-velocity test. Both groups had similar preexercise and end-of-recovery oxygen consumption (VO2), but the young athletes had higher peaks of response (p < .001). The VO2 magnitudes of response increased during the test (p < .01) in all subjects, with higher values for the young athletes (p < .001). There was a positive correlation between the VO2 magnitude of response and (1) the corresponding sprint power output (R = .58,p < .001) and (2) the corresponding number of sprint repetitions (R = .29, p < .02). The young athletes had higher end-of-recovery and peak carbon dioxide production (VCO2) responses than the master athletes (p < .001). Pulmonary ventilation (V(E)) peaks of response to the sprints were higher in the young athletes (p < .001). There was a positive relation between the V(E) and VCO2 peaks of response (R = 84,p < .001). In both groups the peak heart rate, VO2, VCO2, and V(E) values attained during the force-velocity test represented similar percentages of the maximal values reached at exhaustion of maximal graded exercise. These results showed that aging does not alter the percentage of the cardiorespiratory response to a brief intense intermittent exercise such as the force-velocity test. Moreover, the arterial blood pressure response is not significantly altered, whereas the vasodilatatory response is.

Does beta-alanine activate more than one chloride channel associated receptor?

In order to define which receptor-channel complexes are activated by beta-alanine, we performed cross-desensitization experiments between this amino acid and the classical inhibitory neurotransmitters, glycine and gamma-aminobutyric acid (GABA), all of which increase chloride conductances. Using the whole-cell patch-clamp technique and cultured chick spinal neurons, we found that beta-alanine completely desensitizes the glycine response, and only partially reduces GABA evoked currents. No interaction occurred between GABA and glycine at the level of their respective receptors. Conversely, both GABA and glycine reduced the beta-alanine response. These results indicate that beta-alanine activates the glycine receptor, and also suggest that it could be a partial agonist of GABAA receptor(s).

On the elastic properties of tetramethylrhodamine F-actin.

(Iodoacetamido)tetramethylrhodamine disrupts F-actin. At the 1:1 fluorophore to actin (as monomer) ratio approximately 80% of the protein becomes non-sedimentable. The fluorescent, non-sedimentable actin copolymerizes with G-actin to yield fluorescent filaments. The tensile strength of these filaments changes with the ratio of the fluorescent non-sedimentable actin to the G-actin, being 1.6 pN, 2.9 pN and 3.6 pN at the 1/4, 2/3 and 1/1 ratios, respectively. These tensile strengths are approximately two orders of magnitude lower than those obtained by decoration of F-actin with phalloidin.

[Determination of transmitral blood flow by pulsed echodoppler. Correlation with aortic blood flow in 30 patients]. / Détermination du débit transmitral par écho-doppler pulsé, corrélation avec le débit aortique chez 30 patients.

The aim of this study was to assess the validity of mitral valve blood flow measured by pulsed Doppler echocardiography (PDE) with the sample volume positioned at the tips of the mitral leaflets. Thirty patients with a mean age of 38.4 years underwent calculation of transmitral blood flow: by Touche's method (A) in which the mitral orifice is assumed to be an ellipse with a constant long axis equal to the diameter of the mitral annulus and a variable short axis equal to the distance between the mitral leaflets measured on the M mode recording. The velocities are recorded by PDE with the sample volume at the tips of the mitral leaflets. The instantaneous cardiac output is equal to the surface multiplied by the instantaneous velocity. The integration of the instantaneous outputs throughout the whole of diastole by a computer programme provides the stroke volume; by a simplification of this method (B) which considers the short axis of the mitral ellipse to be constant and equal to the mean mitral valve leaflet separation measured from the M mode recording, and; by Hoit's method (C) which calculates mitral valve surface area from the M mode recording alone. The transmitral blood flow was calculated by these three methods and compared to the classical PDE aortic cardiac output measurement during the same examination, the accuracy of which has been previously demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)

[Evaluation by Doppler ultrasound of the severity of aortic stenoses. Application of the continuity equation]. / Evaluation par écho-doppler de la sévérité des sténoses aortiques. Application de l'équation de continuité.

In order to assess the validity of the continuity equation applied to doppler ultrasound in the evaluation of stenotic aortic valve areas, the authors have compared the results obtained in 24 patients examined by catheterization and doppler-echocardiography. In addition, 10 patients who underwent aortic dilatation also had both types of examination, which brings up to 34 the number of comparisons. In haemodynamics, the Gorlin formula was taken as reference for valve area measurement. The doppler-echocardiographic examination, performed 48 hours before, and sometimes after catheterization, recorded sub- and trans-stenotic pressures and outflow tract diameter for application of the continuity equation. Aortic valve areas calculated from doppler data on mean velocities correlated well with areas calculated from haemodynamic data (r = 0.88, p less than 0.001, e = 14 mm2, n = 34). Correlation was even closer when maximum velocities were used (r = 0.96, p less than 0.001, e = 8 mm2, n = 34). When only tight aortic stenoses with a less than 0.75 cm2 area were considered, the correlation remained very good (r = 0.87, p less than 0.001, e = 6 mm2, n = 34). This study therefore demonstrates the reliability of the continuity equation and of the simplified method using maximum sub- and trans-stenotic pressures without having recourse to planimetry. The accuracy of the method is dependent upon 3 parameters: 1. A maximum velocity jet must be obtained, which in turn depends on the investigator's experience and on the sensitivity of the equipment. 2. The velocity recorded by pulsed doppler ultrasound must be "representative" of flow in the outflow tract.(ABSTRACT TRUNCATED AT 250 WORDS)

[Contribution of transesophageal echocardiography in the diagnosis of intra- and para-cardiac masses]. / Apport de l'échocardiographie transoesophagienne dans le diagnostic des masses intra- et paracardiaques.

The authors detected 59 thrombi and 7 intra- or paracardiac tumors in 58 patients in a series of 1,100 transesophageal echocardiography. Twenty-six of the 51 patients with a thrombus were in sinus rhythm; 25 had atrial fibrillation. In 44 cases, the thrombus was single and in 7 cases there were multiple thrombi. A phenomenon of spontaneous contrast in the left atrium was observed in 24 patients (47%). In 31 cases (53%) the thrombi were located in the left auricle, in 21 cases (36%) in the left atrium, in 4 cases in the left ventricle and in 3 cases in the right atrium. Transthoracic echocardiography only detected 25% of these thrombi. The superiority of transesophageal echocardiography was particularly evident for the detection of thrombi in the left auricle (31 by transesophageal echocardiography versus 2 by transthoracic echocardiography) and in the left atrium (13 by transesophageal echocardiography versus 7 by transthoracic echocardiography). Five myxomas were diagnosed by transesophageal echocardiography and 4 of them were identified by transthoracic echocardiography. The site of implantation of the tumor was located in all 5 cases by transesophageal echocardiography. Two right paracardiac tumours were only visible by transesophageal echocardiography. Transesophageal echocardiography is therefore very useful in the diagnosis of thrombi in the left atrium and auricle, of rare hypodense myxomas and paracardiac tumors. In addition, it enables precise localisation of the site of implantation of nearly all intracardiac tumors.

[Value of the continuous Doppler in the evaluation of gradients of aortic valvular stenosis in the adult]. / Valeur du Doppler continu dans l'évaluation des gradients des sténoses aortiques valvulaires de l'adulte.

The purpose of this study, performed in 80 patients with aortic valve stenosis, was to find out whether continuous wave doppler ultrasound was reliable in assessing the severity of the stenosis. Maximum mean and instantaneous transaortic pressure gradients obtained by continuous wave doppler were compared with maximum mean instantaneous and peak to peak gradients simultaneously obtained by cardiac catheterization. 35 patients who underwent aortic valve dilation were explored beforehand and afterwards, which brings up to 115 the total number of gradient comparisons. There was a correlation between maximum instantaneous gradient at doppler and peak to peak gradient (r = 0.62, n = 115, e = 22.5 mmHg, p less than 0.001). A similar correlation was found between maximum instantaneous gradients at doppler and haemodynamics (r = 0.64, n = 80, e = 24.5 mmHg), but correlation between mean gradients was weaker (r = 0.57, n = 80, e = 17.7 mmHg). Maximum and mean instantaneous gradients are underestimated by the doppler method. After exclusion of imperfect doppler curves, correlations were better, notably as regards mean gradients (r = 0.80, n = 18, e = 11.9 mmHg). There was a closer correlation between doppler maximum instantaneous gradients and haemodynamic peak to peak gradients in patients without aortic regurgitation (r = 0.71, n = 45, e = 17.2 mmHg) than in patients with aortic regurgitation (r = 0.54, n = 70, e = 24.3 mmHg).(ABSTRACT TRUNCATED AT 250 WORDS)

[Echodoppler evaluation of the normally functioning Saint-Jude's aortic valve prosthesis]. / Evaluation par écho-doppler du fonctionnement normal de la prothèse de Saint-Jude en position aortique.

The aims of this study were: to define Doppler echocardiographic criteria of normality of aortic St Jude Medical (SJM) valve prostheses with respect to their size and to verify the validity of the continuity equation in the determination of prosthetic valve functional surface area. Forty patients with apparently normally functioning SJM prostheses without other cardiac disease were investigated at least one month after surgery. The group consisted in 1 n. 19, 6 n. 21, 9 n. 23, 12 n. 25 and 12 n. 27 SJM prostheses. The following parameters were measured: the maximum transprosthetic velocity, maximum and mean transprosthetic pressure gradients, permeability index and the Doppler surface area calculated by the continuity equation using the method proposed by Skjaerpe. The global results were as follows: maximum velocity = 2.5 +/- 0.4 m/s (1.8-3.7 m/s); maximum gradient = 26.9 +/- 9.8 mmHg (14-53 mmHg); mean gradient = 13.7 +/- 5.6 mmHg (7-30 mmHg); permeability index = 0.41 +/- 0.09 (0.23-0.57); Doppler surface area = 1.89 +/- 0.66 cm2 (0.73-3.23 cm2). When the prostheses were considered according to their sizes a weak negative correlation was observed between the mean pressure gradients and the size of the prostheses: r = -0.43, p less than 0.05 and a positive correlation between Doppler surface area and the theoretical prosthetic surface area: r = 0.71, p less than 0.005; SD = 0.45 cm2. No significant differences were observed between the pressure gradients and velocities of each size of prosthesis except when sizes 21 + 23 were compared with the large sizes (n. 25 + 27).(ABSTRACT TRUNCATED AT 250 WORDS)