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Biomedical subjects

J Grandjean

Publications and source records attributed to J Grandjean.

At least 19 recordsLinked to original sources
PubMed1997

Verapamil reduces tachycardia-induced electrical remodeling of the atria.

BACKGROUND: Prolonged periods of atrial fibrillation or rapid atrial pacing induce shortening of the atrial effective refractory period (AERP), which is thought to be related to the lower success rates of various antifibrillatory treatments when the arrhythmia has lasted for a longer period of time. METHODS AND RESULTS: To investigate whether an increase in intracellular calcium could be the stimulus for electrical remodeling, the effects of verapamil on shortening of the AERP in response to 24 hours of rapid atrial pacing (300 bpm) were studied in five chronically instrumented conscious goats during infusion of saline or verapamil. During rapid atrial pacing, the ventricular rate was kept constant by ventricular pacing (150 bpm). The AERP was measured by programmed electrical stimulation at basic cycle lengths of 430, 300, and 200 ms. Verapamil had no effects on the AERP before rapid atrial pacing. However, in the course of 24 hours of rapid atrial pacing, the AERP shortened significantly less (27% to 58%) in the presence of verapamil compared with control (at 430, 300, and 200 ms, P < .001, P < .01, and P < .01, respectively). Also, after cessation of pacing, complete recovery of the AERP during verapamil infusion occurred much sooner than in the control experiments. Despite a significant reduction in electrical remodeling, there was only a minimal reduction in inducibility of atrial fibrillation by verapamil (34% versus 39% in the control experiments, P = .03). CONCLUSIONS: Electrical remodeling of the atrium during rapid atrial pacing was significantly attenuated by verapamil. This suggests that electrical remodeling of the atrium is triggered by the high calcium influx during rapid atrial pacing rates.

Animals↗
PubMed1997

Multinuclear Magnetic Resonance Studies on Aqueous Suspensions of Synthetic Saponites

The structure at the liquid/solid interface of synthetic saponites is monitored by NMR methods. These results are compared with data obtained with a natural saponite. The mean orientation of interfacial water molecules is different for synthetic and natural saponites. Interaction of water molecules or counterions with the solid surface depends on the charge layer of the synthetic clays. Water/acetonitrile and sodium/tetrapropylammonium cation competitions have been studied. Significant changes of the orientation of interfacial water molecules and removal of sodium counterions are observed only with the lowest charged saponite.

Journal Article↗
PubMed1997

NOTE

2H NMR quadrupolar splittings of clay suspensions monitor the orientation of water molecules near the solid surface. Two limiting water interfacial sites explain our results on montmorillonite, hectorite, and saponite suspensions. The location of cation isomorphous substitution and the Ca2+/Na+ molar ratio of exchangeable cations modulate their relative importance. With beidellite suspensions, water orientation at the clay surface cannot be described within the above scheme.

Journal Article↗
PubMed1996

Interaction of nonionic polymers at a clay interface.

The structure and dynamics at the interface of swelling clays (smectites) are crucial to such diverse applications as drilling for oil, cosmetics, paints, water treatment, or chemical reactions. From our previous NMR studies on clay suspensions, we have shown how the orientation of interfacial molecules is affected by the clay structure1, by the nature of counterions 2, or by the composition of the liquid phase3. These results have been mainly obtained from the analysis of residual quadrupolar splittings of nuclei from interfacial species. In this work, we report our studies on a clay montmorillonite suspended in aqueous solutions of non ionic polymers. The polymer perturbs the structure within the interfacial region as deduced from the variations of the splittings of water quadrupolar nuclei and of sodium-23 relaxation parameters in terms of the polymer concentration. Proton self-diffusion coefficients and carbon-13 relaxation times are measured to describe the influence of the clay on the polymer mobility. The dependence of the polymer nature on these parameters is also investigated.

Aluminum Silicates↗
PubMed1995

Video assisted coronary bypass surgery.

An alternative way to revascularize coronary vessels is described, using arterial conduits without extracorporeal circulation. The heart is exposed via a small thoracotomy over the fifth left intercostal space. A thoracoscope is introduced into the thorax, to assist in the harvesting of the left internal mammary artery (LIMA). In selected patients with two or three vessel disease, the same procedure can be achieved on the right side, harvesting the right internal mammary artery to revascularize the right coronary artery. The gastroepiploic artery can be easily reached and used to revascularize the posterior descending artery, through a mini-subxiphoid median laparotomy. This technique was used to revascularize 30 patients from April 1994 to June 1995. All received a LIMA graft to the left anterior descending artery, and two had a free radial artery graft from the LIMA, sequentially bypassing the diagonal and obtuse marginal branches. There was neither perioperative mortality nor morbidity myocardial infarction. Fifteen patients were restudied angiographically before discharge. Average hospital stay was 43 +/- 11 hours.

Aged↗
PubMed1987

Ion transport by lasalocid A across red-blood-cell membranes. A multinuclear NMR study.

Na+ and K+ fluxes mediated by lasalocid A across erythrocyte membranes have been determined from 23Na-NMR peak areas and chemical shifts, respectively. In similar experiments, Cl- transport has been monitored by NMR signal intensities. Taking into account the external pH variations, the results are readily explainable in terms of charge-balance conservation. The effect of disodium 4,4'-diisothiocyanostilbene-2,2'-disulfonate, an anion-exchange inhibitor, has also been studied.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1985

Arterial metabolism as studied in vitro by NMR: preliminary results in normotensive and hypertensive aortas.

Arterial tissue has been analysed by 31P-, 13C-, 23Na- and 1H-NMR spectroscopy. Rabbit thoracic aortas were mounted on a system with perfusate circulation and studied in basal conditions. Phosphorus spectra remained stable for hours and showed low levels of phosphocreatine (PCr) compared to skeletal, cardiac or even to nonvascular smooth muscle. Significant levels of sugar-phosphates (SP), phosphodiesters (PDE) were detected, as well as occasionnally a peak in the diphosphodiester region. Experiments with phosphate-free perfusate demonstrated a very low level of intracellular inorganic phosphate. As expected from previous data, free ADP levels in tonic arterial tissue were found much higher than in any other muscle. Addition of norepinephrine into the perfusate induced transient decrease in ATP and PCr levels, associated with an increased production of phosphorylated intermediates. At the early stage of renovascular hypertension, aortic energetic pattern was characterized by an increased ADP/ATP ratio. Natural abundant 13C spectra were recorded from dog aortic fragments and showed mainly resonances attributed to fatty components. After addition of a shift-reagent, dysprosium tripolyphosphate, 23Na-NMR allowed separation of intra- and extracellular Na of perfused rabbits aortas. Proton NMR of lyophilized aortic fragments revealed several peaks originating from biologically relevant molecules, lactate, creatine, taurine... These preliminary data demonstrate the feasability of multinuclear NMR spectroscopy of vascular tissue and are suggestive of the potential of the method when it will be combined with monitoring of functional parameters.

Adenosine Diphosphate↗
PubMed1983

A synthetic crown ether carboxylic acid ionophore displays synergistic transport of Pr3+ in conjunction with lasalocid.

Transport of Pr3+ across phosphatidyl choline vesicles, as monitored by 31P nmr, is second-order in the crown ether carboxylic acid 2, as it is with respect to lasalocid (X-537 A). When the synthetic (2) and the natural (lasalocid) ionophores are incorporated together in approximately 3:1 ratio into the lipidic phase, the transport velocity is markedly enhanced.

Animals↗
PubMed1982

[NMR study of fixation of sodium cations to bovine Gla protein].

Decalcified bovine Gla protein binds sodium cations on the three gamma-carboxylglutamic (Gla) residues. Sodium-23 nuclear magnetic resonance serves to determine the correlation time tau c of bound sodium ions. Its value (tau c = 2.5 ns) matches the reorientational correlation time of the protein (tau R = 2.6 ns).

1-Carboxyglutamic Acid↗
PubMed1980

Sodium-23 nuclear magnetic resonance as an indicator of sodium binding to troponin C and tryptic fragments, in relation to calcium content and attendant conformational changes.

The relaxation rate enhancements of the 23Na nuclei for NaHCO3 solutions of troponin C and its tryptic peptides TR-1 and TR-2 indicate true binding of Na+ ions to these biomolecules. The low-affinity sites I and II of TR-1 and troponin C are the sites of competitive Na+/Ca2+ binding, below one calcium ion per molecule, with log KNa approximately 2. At low calcium content Na+ ions bind to TR-2 and to troponin C non-competitively with Ca2+ ions; binding of Ca2+ ions to the high-affinity sites III and IV allosterically affects the binding of the Na+ ions: even when sites I and II, located on TR-1 or sites I, II, III, IV of troponin C, are saturated with Ca2+ ions, Na+ ions continue to bind weakly at secondary binding sites.

Animals↗
PubMed1980

Sodium-23 nuclear magnetic resonance as an indicator of sodium binding to calmodulin and tryptic fragments, in relation to calcium content.

The relaxation rate enhancements of the 23Na nuclei for NaHCO3 solutions of calmodulin and its tryptic peptides TR-1 and TR-2 indicate true binding of Na+ ions to these biomolecules. With both TR-1 and TR-2, Na+ binding occurs in competition with Ca2+ and Mg2+ binding: log KNa approximately equal to 2, log KMg apoproximately equal to 4, log KCa approximately equal to 6 for TR-1; and log KNa approximately equal to 2, log KMg approximately equal to 3, log KCa approximately equal to 5 for TR-2. All the binding constants are systemically greater for binding to TR-1, as compared to TR-2. There is also an increase in KNa for TR-1 of calmodulin as compared to the homologous tryptic fragment of troponin C. The increased binding is identified tentatively with site I of calmodulin. The binding constants KNa, KCa and KMg of calmodulin appear to be finely tuned to the intracellular concentrations of these cations.

Animals↗