Biomedical subjects
Publications and source records attributed to D J Keller.
Merely ten years after its invention, the scanning force microscope is becoming a powerful method to investigate the structure and dynamics of biological molecules under aqueous environments. From the visualization of transcription in real time to the mechanical manipulation of individual proteins, the advances made during the past year open up a vast number of exciting applications of this technique in biology.
Scanning force microscope images of membrane-bound Escherichia coli ATP synthase F0 complexes have been obtained in aqueous solution. The images show a consistent set of internal features: a ring structure which surrounds a central dimple and contains an asymmetric lateral mass. Images of trypsin-treated F0 complexes, which have lost part of their b subunits, show a reduced asymmetric mass, while images of c-subunit oligomers, which lack both the a and b subunits, show a ring and dimple but do not have an asymmetric mass. These results support models in which the F0 complex contains a ring of 9-12 c subunits with the b subunits located outside this ring, and show that scanning force microscopy is able to provide structural information on membrane proteins of molecular mass less than 200 000 Da.
The purpose of this study was to determine whether a subthreshold dose of cocaine (one that is well-tolerated in a resting state with no significant hemodynamic changes) causes cardiotoxic responses when superimposed upon a subthreshold infusion of norepinephrine. Adult mongrel dogs were anesthetized, instrumented and assigned to one of five treatment groups: saline control, norepinephrine infusion (0.75 microgram/kg/min, i.v. for 60 min); cocaine (5.0 mg/kg, i.v. bolus); combination of cocaine (0.5 mg/kg) or (5.0 mg/kg) with the last 45 min of norepinephrine infusion. The combination groups exhibited increased blood pressure and contractility (dP/dt), and a greater variety and frequency of arrhythmias. Cocaine did not increase plasma catecholamine levels beyond norepinephrine alone. There were significantly more contraction band lesions/mm2 with cocaine in combination with norepinephrine than in any of the individual treatment groups. These data indicate that, even in anesthetized animals, a well-tolerated dose of cocaine may become toxic when superimposed on an excited or hyperadrenergic state with elevated levels of norepinephrine.
Molecules of the transcriptional enzyme E. coli RNA polymerase (RNAP) have been deposited using three different deposition methods: (1) passive adsorption onto gold, (2) electrochemical adsorption onto gold and (3) adsorption onto mica. In all cases SFM imaging was straightforward and reliable, and surface coverage by the protein varied with deposition conditions as expected. To determine the nature of the electrochemical treatment on the gold substrate, cyclic voltammetry was performed with various chemical solutions. Finally, a comparison is made between the SFM images of RNAP obtained with these methods and STM images obtained earlier. Both STM and SFM show strikingly similar results; however, heights and widths of individual molecules differ.
Membrane bilayers of dipalmitoyl phosphatidylcholine (DPPC) and dipalmitoyl phosphatidylethanolamine (DPPE) adsorbed to a freshly cleaved mica substrate have been imaged by Atomic Force Microscopy (AFM). The membranes were mounted for imaging by two methods: (a) by dialysis of a detergent solution of the lipid in the presence of the substrate material, and (b) by adsorption of lipid vesicles onto the substrate surface from a vesicle suspension. The images were taken in air, and show lipid bilayers adhering to the surface either in isolated patches or in continuous sheets, depending on the deposition conditions. Epifluorescence light-microscopy shows that the lipid is distributed on the substrate surfaces as seen in the AFM images. In some instances, when DPPE was used, whole, unfused vesicles, which were bound to the substrate, could be imaged by the AFM. Such membranes should be capable of acting as natural anchors for imaging membrane proteins by AFM.
During the 1977-78, 1978-79, and 1979-80 ski seasons, 76 acute anterior shoulder dislocations were treated by one of three Orthopedic Surgeons at the Rutland Vermont Hospital Emergency Room: 68 (89.4%) were reduced on first attempt using the Milch technique of abduction and external rotation. Four (5.2%) required general anesthesia and four were reduced using meperidine hydrochloride (Demerol, Winthrop) and diazepam (Valium, Roche) and a traction-countertraction technique. Of the 68 shoulders reduced with the Milch technique, 47 (69.1%) required no analgesics or muscle relaxants. There were no complications attributable to the technique itself. Males were injured more frequently than females in a 4.4:1 ratio. Left shoulder injuries were as common as right. Recurrent dislocations occurred more frequently in younger individuals. Fractures of the greater tuberosity were associated injuries in five (6.6%) of all dislocations. These all occurred in individuals older than age 39 years and were coincident with primary dislocations.
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