Faculty Bibliography

OBJECTIVES: To create and test a dissected bovine heart model (BHM) to facilitate the interpretation of cardiac sonography (CS). METHODS: After a pretest and an instructional video on CS, emergency physicians (EPs) were randomized into two groups. Group 1 viewed two-dimensional (2D) anatomic pictures of human hearts. Group 2 examined the BHM and the same anatomic pictures as group 1. The EPs retook the pretest. The differences between the raw pretest and posttest scores of the groups were compared with an unpaired Student's t-test. Multiple linear regression was used to adjust for confounding by variation in education and initial test scores. EPs with previous experience in CS were excluded from the analysis. RESULTS: Thirty-five participants met the inclusion criteria, 16 in group 1 and 19 in group 2. The groups were well balanced with respect to postgraduate year training. The EPs in group 1 had a higher average pretest score of 11.6 versus 8.1 in group 2. Compared with the pretest scores, the average improvements in group 1 and group 2 were 7.6 and 11.3 points, respectively. Group 2 improved an average of 3.7 points (95% confidence interval [95% CI] = 0.7 to 6.7; p = 0.016) more than group 1. After adjusting for confounding by the difference in initial scores, group 2 improved 1.8 (95% CI = -1.1 to 4.8; p = 0.22) more points on average than group 1. CONCLUSIONS: A dissected bovine heart model did not significantly improve the ability of EPs to label structures on static ultrasounds over inspection of static-labeled anatomic pictures alone

Ribophorins I and II are two transmembrane glycoproteins that are characteristic of the rough endoplasmic reticulum and are thought to be part of the apparatus that affects the co-translational translocation of polypeptides synthesized on membrane-bound polysomes. A ribophorin I cDNA clone containing a 0.6-kb insert was isolated from a rat liver lambda gtll cDNA library by immunoscreening with specific antibodies. This cDNA was used to isolate a clone (2.3 kb) from a rat brain lambda gtll cDNA library that contains the entire ribophorin I coding sequence. SP6 RNA transcripts of the insert in this clone directed the in vitro synthesis of a polypeptide of the expected size that was immunoprecipitated with anti-ribophorin I antibodies. When synthesized in the presence of microsomes, this polypeptide, like the translation product of the natural ribophorin I mRNA, underwent membrane insertion, signal cleavage, and co-translational glycosylation. The complete amino acid sequence of the polypeptide encoded in the cDNA insert was derived from the nucleotide sequence and found to contain a segment that corresponds to a partial amino terminal sequence of ribophorin I that was obtained by Edman degradation. This confirmed the identity of the cDNA clone and established that ribophorin I contains 583 amino acids and is synthesized with a cleavable amino terminal insertion signal of 22 residues. Analysis of the amino acid sequence of ribophorin I suggested that the polypeptide has a simple transmembrane disposition with a rather hydrophilic carboxy terminal segment of 150 amino acids exposed on the cytoplasmic face of the membrane, and a luminal domain of 414 amino acids containing three potential N-glycosylation sites. Hybridization measurements using the cloned cDNA as a probe showed that ribophorin I mRNA levels increase fourfold 15 h after partial hepatectomy, in confirmation of measurements made by in vitro translation of liver mRNA. Southern blot analysis of rat genomic DNA suggests that there is a single copy of the ribophorin I gene in the haploid rat genome

Ribophorins are two transmembrane glycoproteins characteristic of the rough endoplasmic reticulum, which are thought to be involved in the binding of ribosomes. Their biosynthesis was studied in vivo using lines of cultured rat hepatocytes (clone 9) and pituitary cells (GH 3.1) and in cell-free synthesis experiments. In vitro translation of mRNA extracted from free and bound polysomes of clone 9 cells demonstrated that ribophorins are made exclusively on bound polysomes. The primary translation products of ribophorin messengers obtained from cultured hepatocytes or from regenerating livers co-migrated with the respective mature proteins, but had slightly higher apparent molecular weights (2,000) than the unglycosylated forms immunoprecipitated from cells treated with tunicamycin. This indicates that ribophorins, in contrast to all other endoplasmic reticulum membrane proteins previously studied, contain transient amino-terminal insertion signals which are removed co-translationally. Kinetic and pulse-chase experiments with [35S]methionine and [3H]mannose demonstrated that ribophorins are not subjected to electrophoretically detectable posttranslational modifications, such as proteolytic cleavage or trimming and terminal glycosylation of oligosaccharide side chain(s). Direct analysis of the oligosaccharides of ribophorin l showed that they do not contain the terminal sugars characteristic of complex oligosaccharides and that they range in composition from Man8GlcNAc to Man5GlcNAc. These findings, as well as the observation that the mature proteins are sensitive to endoglycosidase H and insensitive to endoglycosidase D, are consistent with the notion that the biosynthetic pathway of the ribophorins does not require a stage of passage through the Golgi apparatus