GLUT4 and transferrin receptor are differentially sorted along the endocytic pathway in CHO cells

The trafficking of GLUT4, a facilitative glucose transporter, is examined in transfected CHO cells. In previous work, we expressed GLUT4 in neuroendocrine cells and fibroblasts and found that it was targeted to a population of small vesicles slightly larger than synaptic vesicles (Herman, G.A, F. Bonzelius, A.M. Cieutat, and R.B. Kelly. 1994. Proc. Natl. Acad. Sci. USA. 91: 12750-12754.). In this study, we demonstrate that at 37 degrees C, GLUT4-containing small vesicles (GSVs) are detected after cell surface radiolabeling of GLUT4 whereas uptake of radioiodinated human transferrin does not show appreciable accumulation within these small vesicles. Immunofluorescence microscopy experiments show that at 37 degrees C, cell surface-labeled GLUT4 as well as transferrin is internalized into peripheral and perinuclear structures. At 15 degrees C, endocytosis of GLUT4 continues to occur at a slowed rate, but whereas fluorescently labeled GLUT4 is seen to accumulate within large peripheral endosomes, no perinuclear structures are labeled, and no radiolabeled GSVs are detectable. Shifting cells to 37 degrees C after accumulating labeled GLUT4 at 15 degrees C results in the reappearance of GLUT4 in perinuclear structures and GSV reformation. Cytosol acidification or treatment with hypertonic media containing sucrose prevents the exit of GLUT4 from peripheral endosomes as well as GSV formation, suggesting that coat proteins may be involved in the endocytic trafficking of GLUT4. In contrast, at 15 degrees C, transferrin continues to traffic to perinuclear structures and overall labels structures similar in distribution to those observed at 37 degrees C. Furthermore, treatment with hypertonic media has no apparent effect on transferrin trafficking from peripheral endosomes. Double-labeling experiments after the internalization of both transferrin and surface-labeled GLUT4 show that GLUT4 accumulates within peripheral compartments that exclude the transferrin receptor (TfR) at both 15 degrees and 37 degrees C. Thus, GLUT4 is sorted differently from the transferrin receptor as evidenced by the targeting of each protein to distinct early endosomal compartments and by the formation of GSVs. These results suggest that the sorting of GLUT4 from TfR may occur primarily at the level of the plasma membrane into distinct endosomes and that the organization of the endocytic system in CHO cells more closely resembles that of neuroendocrine cells than previously appreciated.

Clinical teaching in physical therapy education. An ethnographic study

The purpose of this ethnographic study was to examine the process of clinical education from the viewpoint of clinical teachers. A three-month field study based on a grounded theory approach and involving simultaneous collection and codification of data led to the discovery and explication of two major components of the clinical education process. One component, the clinical teaching situation, identified the organizational and human factors that influence the type, quality, and quantity of the student learning. The second component, teaching tools used by the clinical teachers, identified the strategies used to pace the student to professional competence. The authors view the findings as a beginning understanding of how and why clinical education is fundamentally different from academic education.

Class of 1980

The purpose of this study was to collect and summarize comprehensive demographic data and other information about students graduating from entry-level physical therapy education programs. A survey of graduating students from 83 institutions with approved programs listed in the October 1979 issue of Physical Therapy resulted in responses from 2,280 students from 81 institutions. The findings present a description of the 2,280 respondents and profiles for male and female students and for graduates of different types of entry-level programs. This information should be useful to those involved with educational programs, the professional Association, and other individuals as they make decisions and plan educational strategies for the preparation of future physical therapists.