Biomedical subjects
Publications and source records attributed to F Heitz.
Chest radiographs of 11 patients with supero-inferior ventricles proven by echocardiography and angiocardiography are presented. The main feature is the modified configuration of the left heart contour. Even if not specific, this sign is encountered frequently (72%) and may suggest the diagnosis.
M-mode echocardiographic features suggesting a patent ductus arteriosus are based on two groups of indirect criteria: dilation of the left cardiac cavities and changes of systolic time intervals. The reliability of the first group of criteria has been questioned in fluid-limited, mechanically ventilated preterm infants. The sensitivity of the systolic time intervals in the same circumstances is investigated. Twenty-three patients with a large patent ductus arteriosus were selected. Review of their echocardiograms shows that the sensitivity of the various criteria (expressed as percentage of positivity) was as follows: inversion of the ratio of left ventricular preejection period to right ventricular preejection period, 91.3%; left ventricular preejection period to left ventricular ejection time over right ventricular preejection period to right ventricular ejection time less than 1,83%; left atrium dilation, 74%; shortening of left ventricular preejection period, 70%; dilation of left ventricular internal dimensions in diastole, 65%; increase in left atrium/aorta, 52%; and decrease of left ventricular preejection period to left ventricular ejection time, 48%. Three criteria involving time intervals (left ventricular preejection period to right ventricular preejection period, left ventricular preejection period, and left ventricular preejection period to left ventricular ejection time) had 100% specificity. The lowest specificity was found with criteria involving the left atrium (left atrial to aortic root ratio 75% and left atrium 63%). It is concluded that study of systolic time intervals is a reliable means of detecting preterm infants with hemodynamically significant left-to-right shunt through a patent ductus arteriosus even if the infants are mechanically ventilated and fluid restricted.
Proteolipid apoproteins have been isolated from a whole bovine brain homogenate by chloroform/methanol extraction, and fractionated by chromatography on modified (lipophilic) Sephadex, followed by ion-exchange chromatography on CM-Trisacryl. The various final, highly hydrophobic, fractions are homogeneous (sodium dodecyl sulfate/polyacrylamide gel electrophoresis). Transmembrane ion transfers were studied by 22Na + flux and electrical conductance measurements. Single channel events were observed at low protein concentrations, in particular with one of the final homogeneous apoproteolipids of molecular mass 24 kDa.
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From spectroscopic data (infrared, CD and 13C-NMR) it is shown that Ca2+ interacts with gramicidin A and that a head-to-head gramicidin A dimer can have two Ca2+-binding sites located near the COOH termini. On the basis of this result, we can propose an explanation for the blocking effect of Ca2+ on the transport of alkali metal ions (Cs+ and K+) through gramicidin channels. The binding of Ca2+ is competitive with the alkali metal ion binding; Ca2+ cannot cross the gramicidin channel and its binding in the channel is voltage dependent. From the proposed model, it is possible to account for the influence of the addition of Ca2+ on the single-channel limiting conductance and on the variation of the single-channel current as a function of the voltage in the presence of Cs+ or K+.
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Analysis of the single-channel behavior of an analogue of gramicidin A in which all four tryptophyl residues are substituted by phenylalanyl suggests that the nature of the side chains may play an important role in the ion translocation process. Indeed, while infrared spectroscopy indicates that both peptides have very similar backbone conformations, they have different single-channel characteristics. The unit conductance of the analogue is much smaller than that of the natural product. Moreover, contrary to gramicidin A, it is voltage dependent.
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From infrared observations it is concluded that the conformation of poly (D Trp-L leu), poly (D Leu-L Trp), poly (D Phe-L leu) and poly (D val-L Val-D Val-L Ala) wich are model polymers of Gramicidin A is the same as one species of the antibiotic. Diffraction investigations indicate that poly-(D Phe-L Leu) and poly (D Val-L Val-D Val-L Ala) have a helical conformation which is most probably the pi DL 8 helix.
On the basis of the finding of two sets of coupling constants (8.8 Hz and 6.7 Hz) in the 270-MHz proton magnetic resonance spectra of linear Gramicidin in dimethylsulfoxide and the comparison of its infrared spectrum with those of known conformations of alternating poly(gamma-benzyl-D-glutamate--gamma-benzyl-L-glutamate), it is proposed that the antibiotic has an LD-ribbon structure.
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