镁对在体兔缺血—再灌心脏的电生理效应

本实验通过结扎兔冠状动脉左室支复制动脉缺血－再灌注模型，应用心外膜接触电极记录单相动作电位，观察后除极电位在再灌注性心律失常中及镁离子的拮抗作用。结果表明，再灌性心律失常的５２．６％与早期后去极化有关。硫酸镁可终止及预防ＲＡ，对再灌中出现触发活动有抑制作用。     

Effect of melanin produced by a recombinant Escherichia coli on antibacterial activity of antibiotics.

A recombinant plasmid, pYL-1, containing a tyrosinase gene whose expression is under the control of a phage T5 promoter and 2 lac operators, was constructed. Escherichia coli JM109 harboring pYL-1 was used for production of bacterial melanin. A simple procedure for the isolation and purification of melanin was developed. The ultraviolet (UV)-visible light absorption spectra of melanin prepared by chemical synthesis and derived from different organisms, including bacteria, a plant and an animal source, were determined. Melanins produced by both bacteria and chemical synthesis showed a steady increase of absorption at wavelengths of UV light ranging from approximately 200-400 nm, while melanin derived either from plant or animal sources showed an additional discrete absorption peak at wavelength 280 nm upon a similar steady increase of absorption. This additional absorption peak could be due to the presence of protein-bound melanins in animal and plant sources while a free form of melanin was obtained from bacteria and chemical synthesis. Analysis of the effect of bacterial melanin on the activity of antibiotics against E. coli revealed that the activities of polymyxin B, kanamycin, tetracycline, and ampicillin were markedly reduced in the presence of melanin, whereas the activity of norfloxacin was not affected. The reduction of the antibacterial activity may result directly from the interaction of antibiotics with melanin. However, the mechanism of this interaction remains to be demonstrated.     

A tctex1-Ca2+ channel complex for selective surface expression of Ca2+ channels in neurons

Voltage-gated Ca(2+) channels (VGCCs) are important in regulating a variety of cellular functions in neurons. It remains poorly understood how VGCCs with different functions are sorted within neurons. Here we show that the t-complex testis-expressed 1 (tctex1) protein, a light-chain subunit of the dynein motor complex, interacts directly and selectively with N- and P/Q-type Ca(2+) channels, but not L-type Ca(2+) channels. The interaction is insensitive to Ca(2+). Overexpression in hippocampal neurons of a channel fragment containing the binding domain for tctex1 significantly decreases the surface expression of endogenous N- and P/Q-type Ca(2+) channels but not L-type Ca(2+) channels, as determined by immunostaining. Furthermore, disruption of the tctex1-Ca(2+) channel interaction significantly reduces the Ca(2+) current density in hippocampal neurons. These results underscore the importance of the specific tctex1-channel interaction in determining sorting and trafficking of neuronal Ca(2+) channels with different functionalities.     

The B/C gene of simian virus 40.

Temperature-sensitive B, C, and BC mutants of Simian virus 40 (SV40) map in the late region of the viral genome inHin fragments K, F, J, and G, a DNA segment of about 1200 nucleotide pairs (Lai, C.-J., and Nathans, D. (1975)Virology 66, 70–81). To define the B/C region further, mutants of SV40 with deletions in this genomic segment were constructed by enzymatic excision of DNA from the viral genome, followed by cloning in the presence of a complementing tsA mutant of SV40. After localization of deleted genome segments by analysis of endo R fragments and electron microscopic heteroduplex mapping, selected deletion mutants were tested for complementation by ts mutants and were screened for their ability to produce new viral proteins in infected cells. Complementation tests indicated that B/C deletion mutations are in a cistron distinct from that of tsA and tsD mutations and that the junction between the B/C and D genes is within Hin-K. Two of the deletion mutants produced new proteins detectable in infected cells. More detailed analysis of one of these proteins (of molecular weight 25,000) indicated that it precipitated with antiserum against dissociated SV40 capsids, and that all but one of its lysine-containing tryptic peptides cochromatographed with SV40 VP1 tryptic peptides. We conclude that the B/C gene, containing approximately 1200 nucleotide pairs, codes for VPl. Since deletion mutants lacking Hin-E do not complement B mutants, we suggest that the Hin-E DNA segment has a signal required for expression of the B/C gene.     

Cytoplasmic crystalline inclusions in a anaplastic oligoastrocytoma

A 41-year-old male presented with an ill-demarcated mass involving the left fronto-temporal lobe and the basal ganglia. Light microscopically the tumor was diagnosed as an anaplastic oligoastrocytoma. Electron microscopy revealed several cytoplasmic crystalline inclusions in tumor cells of oligodendroglial lineage. No crystalline inclusions were membrane bound. The morphologic features with unique ultrastructural findings are presented.     

Pulmonary artery angiosarcoma: a clinicopathologic and radiological correlation

A 69-year-old man presented with cough, shortness of breath, and fatigue. He was initially treated for allergies and then for pulmonary embolism. Radiologically, a tumor mass was found to occlude the right pulmonary artery and involve the pulmonary trunk. A right pneumonectomy was performed. Histologically, a cellular malignant spindle and epithelioid tumor with areas of necrosis and brisk mitotic activity was seen. In some areas, the tumor appeared to form vascular channels. Focal osteosarcomatous differentiation was present. Immunohistochemical studies were performed including vimentin, smooth muscle actin, desmin, CD31, CD34, S100, and pan-cytokeratin. The tumor cells were positive for CD31 and vimentin and negative for pan-cytokeratin, CD34, and S100. Two months after surgery, the patient was alive and well.