Cell-to-cell transfer of glial proteins to the squid giant axon: The glia- neuron protein transfer hypothesis

The hypothesis that glial cells synthesize proteins which are transferred to adjacent neurons was evaluated in the giant fiber of the squid (Loligo pealei). When giant fibers are separated from their neuron cell bodies and incubated in the presence of radioactive amino acids, labeled proteins appear in the glial cells and axoplasm. Labeled axonal proteins were detected by three methods: extrusion of the axoplasm from the giant fiber, autoradiography, and perfusion of the giant fiber. This protein synthesis is completely inhibited by puromycin but is not affected by chloramphenicol. The following evidence indicates that the labeled axonal proteins are not synthesized within the axon itself. (a) The axon does not contain a significant amount of ribosomes or ribosomal RNA. (b) Isolated axoplasm did not incorporate [(3)H]leucine into proteins. (c) Injection of Rnase into the giant axon did not reduce the appearance of newly synthesized proteins in the axoplasm of the giant fiber. These findings, coupled with other evidence, have led us to conclude that the adaxonal glial cells synthesize a class of proteins which are transferred to the giant axon. Analysis of the kinetics of this phenomenon indicates that some proteins are transferred to the axon within minutes of their synthesis in the glial cells. One or more of the steps in the transfer process appear to involve Ca++, since replacement of extracellular Ca++ by either Mg++ or Co++ significantly reduces the appearance of labeled proteins in the axon. A substantial fraction of newly synthesized glial proteins, possibly as much as 40 percent, are transferred to the giant axon. These proteins are heterogeneous and range in size from 12,000 to greater than 200,000 daltons. Comparisons of the amount of amino acid incorporation in glia cells and neuron cell bodies raise the possibility that the adaxonal glial cells may provide an important source of axonal proteins which is supplemental to that provided by axonal transport from the cell body. These findings are discussed with reference to a possible trophic effect of glia on neurons and metabolic cooperation between adaxonal glia and the axon.     

Prostaglandin G2 levels during reaction of prostaglandin H synthase with arachidonic acid

Prostaglandin H synthase catalyzes the formation of prostaglandin (PG) G2 from arachidonic acid (cyclooxygenase activity), and also the reduction of PGG2 to PGH2 (peroxidase activity). The ability of the pure synthase to accumulate the hydroperoxide, PGG2, under conditions allowing the concurrent function of both catalytic activities was investigated. The peroxidase velocity was continuously determined from the absorbance increases at 611 nm that accompanied oxidation of a peroxidase cosubstrate, N,N,N',N'-tetramethylphenylenediamine, and PGG2 concentrations were calculated from the peroxidase velocities and the peroxidase Vmax and Km values. Cyclooxygenase velocities were then calculated from the changes in PGG2. Parallel reactions monitored by the use of radiolabelled arachidonate or with a polarographic oxygen electrode were used to confirm the calculated PGG2 levels and the cyclooxygenase velocities. The concentration of PGG2 was found to follow a transient course as the reaction of the synthase progressed, rapidly rising to a maximum of 0.7 microM in the first 10 s, and then declining slowly, reaching 0.1 microM after 60 s. The maximal level of PGG2 achieved during the reaction was constant at about 0.7 microM with higher amounts of added cyclooxygenase capacity (0.3-0.6 microM PGG2/s) but was only about 0.4 microM when the added cyclooxygenase capacity was 0.1 microM PGG2/s. The peroxidase was found to lose only 30% of its activity after 90 s, a point where the cyclooxygenase was almost completely inactive. These results support the concept of a burst of catalytic action from the cyclooxygenase and a reactive, more sustained, catalytic action from the peroxidase during the reaction of the synthase with arachidonic acid.     

Echocardiographic assessment and percutaneous closure of multiple atrial septal defects

Percutaneous coronary intervention can be associated with distal embolization of thrombotic material causing myocardial necrosis and infarction. We discuss the role of intravascular imaging to guide the use of a distal protection device by describing the outcome of a young woman presenting with non-ST elevation myocardial infarction. Coronary angiography demonstrated an isolated minor stenosis in the proximal left anterior descending coronary artery with slight haziness beyond the lesion. Intravascular ultrasound confirmed an extensive thrombus overlying a bulky atherosclerotic plaque. A distal filter wire was therefore successfully used to reduce the risk of distal embolization. The use of intravascular ultrasound in patients presenting with acute coronary syndrome may reveal large thrombi that are difficult to image using conventional angiographic techniques. Intravascular ultrasound can therefore be used as a tool to select lesions requiring distal protection.     

Attachment of substrate metabolite to prostaglandin H synthase upon reaction with arachidonic acid

Prostaglandin H synthase was incubated with [14C]arachidonate and then analyzed by polyacrylamide gel electrophoresis under denaturing conditions and by high pressure liquid chromatography. A maximum of 1 mol of arachidonate metabolite was found to become attached per mol of synthase subunit in a time-dependent process that was much slower than the rate of self-catalyzed inactivation of the cyclooxygenase activity. Incubation of a mixture of the synthase and ovalbumin with [14C]arachidonate resulted in a selective attachment of radiolabel to the synthase. These results suggest the presence of a single site on the synthase that is susceptible to reaction with an arachidonate metabolite.     

Sequence variations in small-subunit ribosomal RNAs of Hartmannella vermiformis and their phylogenetic implications

Evidence of associations between free-living amoebas and human disease has been increasing in recent years. Knowledge about phylogenetic relationships that may be important for the understanding of pathogenicity in the genera involved is very limited at present. Consequently, we have begun to study these relationships and report here on the phylogeny of Hartmannella vermiformis, a free-living amoeba that can harbor the etiologic agent of Legionnaires' disease. Our analysis is based on studies of small-subunit ribosomal RNA genes (srDNA). Nucleotide sequences were determined for nuclear srDNA from three strains of H. vermiformis isolated from the United Kingdom, Germany, and the United States. These sequences then were compared with a sequence previously obtained for a North American isolate by J. H. Gunderson and M. L. Sogin. The four genes are 1,840 bp long, with an average GC content of 49.6%. Sequence differences among the strains range are 0.38%-0.76%. Variation occurs at 19 positions and includes 2 single-base indels plus 14 monotypic and 3 ditypic single-base substitutions. Variation is limited to eight helix/loop structures according to a current model for srRNA secondary structure. Parsimony, distance, and bootstrap analyses used to examine phylogenetic relationships between the srDNA sequences of H. vermiformis and other eukaryotes indicated that Hartmannella sequences were most closely related to those of Acanthamoeba and the alga Cryptomonas. All ditypic sites were consistent with a separation between European and North American strains of Hartmannella, but results of other tests of this relationship were statistically inconclusive.      

Protection of prostaglandin H synthase from trypsin upon binding of heme

The sensitivity of the apo- and holoenzyme forms of prostaglandin H synthase to trypsin have been investigated. Both the cyclooxygenase and peroxidase activities associated with the synthase were rapidly lost from the apoenzyme when incubated with trypsin. However, both activities were resistant to trypsin in the holoenzyme, suggesting that some structural change accompanies heme binding. Inactive protein present in some holoenzyme preparations, although indistinguishable from the synthase subunit by polyacrylamide gel electrophoresis, was also hydrolyzed by trypsin.