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Biomedical subjects

J M Lau

Publications and source records attributed to J M Lau.

15 recordsLinked to original sources
PubMed2000

Atomic force microscopy imaging of living cells: a preliminary study of the disruptive effect of the cantilever tip on cell morphology.

Recent studies have demonstrated that atomic force microscopy (AFM) is a potential tool for studying important dynamic cellular processes in real time. However, the interactions between the cantilever tip and the cell surface are not well understood, and the disruptive effect of the cantilever tip on cell morphology has not been well characterized. In this study, the disruptive effect of the scanning cantilever tip on cell morphology, in the AFM contact mode, has been investigated. The aims of this study are to identify what kinds of cell morphological changes generally occurred under normal AFM imaging conditions and to find out how long cells remain viable during scanning. Two cell lines, SK-N-SH (human neuroblastoma cells) and AV12 (Syrian hamster cells) were studied in the experiment because these are widely used in biomedical research as an expression system for studying cellular functions of neuronal receptors. The experimental results suggest that the sensitivity of cells to the cantilever disruptive effect is dependent on cell type and that there are patterns observed in the changes of cell morphology induced by the cantilever force in these two cell lines.

Animals↗
PubMed1999

Conformational variants of class II MHC/peptide complexes induced by N- and C-terminal extensions of minimal peptide epitopes.

Class II MHC molecules are known to exist in conformational variants. "Floppy" and "compact" forms of murine MHC molecules, for example, are discriminated by their migration behavior on SDS/PAGE and represent empty and ligand-loaded forms. Here we show that formation of distinctly faster-migrating ligand complexes (F-forms) rather than the normal compact (C-) forms of HLA-DR1 or -DR4 results from extensions of minimal peptide epitopes (such as HA306-318 or IC106-120) by approximately 10 amino acids at either the N or the C terminus. Two similar but distinct F-forms (FI and FII) were detected, depending on the site of the extension. Both F-forms were characterized by increased surface hydrophobicity and reduced SDS-stability. Native gel separations and size exclusion chromatography indicated that the F-forms had increased hydrodynamic radii compared with the C-form and an apparent size similar to that of empty MHC molecules. The regions on the ligand overhangs responsible for the effect began at a distance of approximately 5 amino acids on either side of the epitopes, comprised 4-8 amino acids (i.e., a total overhang of 9-14), and did not have a particular sequence preference. The possible functional significance of these forms is discussed.

Antigen Presentation↗
PubMed1994

Persistent postoperative ventricular tachycardia treatment by using external cardiopulmonary support.

Drug-resistant incessant ventricular tachycardia (DRIVT) after cardiac surgery is a rare but almost always fatal event. Antiarrhythmic therapy seems to be ineffective and electrical cardioversion is of limited value when these patients present themselves with recurrent, sustained ventricular tachycardia. A patient with DRIVT in whom external cardiopulmonary support finally succeeded in bringing about resuscitation will be described in this article. The use of external cardiopulmonary support (CPS) should be considered in patients with this kind of malignant arrhythmia.

Aged↗
PubMed1993

A review of the anomalous origin of the left coronary artery from the anterior sinus of Valsalva: is prevention possible?

The origin of the left coronary artery from the anterior sinus of Valsalva is a rare coronary anomaly. Nevertheless, it remains an important pathological entity because of the possibility of its clinical and surgical consequences. Physicians should therefore be aware of this condition and consider it in their differential diagnosis of ischemic heart disease. This is a case report and review of the literature.

Adult↗
PubMed1990

Carotenoid composition, concentrations, and relationships in various human organs.

The carotenoid content of 10 different organs obtained at autopsy from 16 humans was determined using a high-performance liquid chromatography assay. The same qualitative pattern of carotenoids found in serum was found for all the tissues, although there were important quantitative differences in the different carotenoids between organs. The median levels of zeaxanthins, lycopene and beta-carotene varied disproportionately between organs; similar levels of one carotenoid for two organs would not predict similar levels of another carotenoid for the same organs. Similarly, there was not a consistent relationship between all the carotenoids for a given organ. The uneven but wide tissue distribution of most dietary carotenoids may indicate an active biological role for these compounds.

Adult↗
PubMed1985

Testicular gonadal stromal (Sertoli cell) tumor.

Eighty-one cases of testicular gonadal stromal tumor have been reported in the literature. An additional case is herein reported. The pathologic, immunohistologic, and histogenetic aspects are presented.

Carcinoembryonic Antigen↗
PubMed1985

Structure and function of plant cell wall polysaccharides.

Studies of the primary structures of polysaccharides of growing plant cell walls have shown that these structures are far more complex than was anticipated just a few years ago. This complexity can best be appreciated by considering xyloglucan, a hemicellulose present in the cell wall of both monocots and dicots, and rhamnogalacturonan II (RG-II) and rhamnogalacturonan I (RG-I), two structurally unrelated pectic polysaccharides. This realization led us to postulate that cell wall polysaccharides have functions beyond determining the size, shape and strength of plants. Some years ago we demonstrated that oligosaccharide fragments of a branched beta-linked glucan of fungal cell walls can elicit the production of phytoalexins (antibiotics) in plants by inducing the formation of the enzymes responsible for synthesis of the phytoalexins. It has now been ascertained and confirmed by synthesis that the elicitor activity resides in a very specific hepta-beta-D-glucoside. The heptaglucoside has been shown to elicit phytoalexins by activating the expression of specific genes, that is, by causing the synthesis of the mRNAs that encode the enzymes that synthesize phytoalexins. In other words, complex carbohydrates can be regulatory molecules. Further experiments established that oligosaccharide fragments of polysaccharides, produced by acid or base hydrolysis or by enzymolysis of primary cell walls of plants, also evoked defence responses in plants. Subsequently, we learned that defined fragments of polysaccharides, released from covalent attachment within plant cell walls, can function as regulators of various physiological processes such as morphogenesis, rate of cell growth and time of flowering and rooting, in addition to activating mechanisms for resisting potential pathogens. Examples of plant oligosaccharides with regulatory properties (called oligosaccharins) will be described.

Cell Survival↗
PubMed1981

Operative techniques in infective endocarditis.

Twenty-six of 163 patients with infective endocarditis treated between 1969 and 1979 required operation. The consequences of infection in these 26 patients included leaflet destruction, annular "ring" abscess, fistula formation with ventricular and atrial septal perforation, and myocardial abscess with heart block. Surgical principles used to repair these abnormalities successfully were excision of necrotic tissue, valve replacement, repair of annular defects, and closure of perforations. Temporary and permanent cardiac pacing were used also. The operative mortality was 13%.

Abscess↗
PubMed1978

Amebic peritonitis following rupture of an amebic liver abscess. Successful treatment of two patients.

We present two successfully treated cases of amebic peritonitis. Acute peritonitis secondary to intra-abdominal rupture of an amebic liver abscess is an infrequent but serious complication of invasive amebiasis. Its diagnosis should be considered in anyone with a suspected liver abscess, jaundice, or diarrhea in whom peritonitis develops. This diagnosis should be further suggested in the United States if the patient is a male and is of Mexican origin in areas where this racial group constitutes the majority of cases of amebic disease. Use of radioisotope liver scans and the demonstration of serum precipitins to Endamoeba histolytica may provide rapid evidence of invasive disease, although surgical intervention is often necessary to make a specific diagnosis. Emetine hydrochloride alone or followed by metronidazole combined with surgical drainage is the current treatment for amebic peritonitis.

Adult↗