Date of Award

1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Molecular and Cellular Biology and Pathobiology

College

College of Graduate Studies

First Advisor

Maria G. Buse

Second Advisor

Jerome Ondo

Third Advisor

William Gorospe

Fourth Advisor

John Ramsdell

Fifth Advisor

Somsankar Dasgupta

Abstract

Insulin stimulates glucose transport into skeletal muscle upon binding to its cell surface receptor. The signals which stimulate transport are unknown. Studies of insulin's effects on muscle cell lines and adipocytes suggest that increases in sn-l,2-diacyglycerol (DAG) content may mediate insulin-stimulated glucose transport. To test this, the effect of insulin on muscle DAG content was measured. DAG increased in diaphragm and soleus muscles exposed to insulin in vitro and in diaphragm in vivo. However, the supraphysiologic insulin dose (60 nM) and incubation time required (10 min) are not consistent with a role for DAG as a mediator of insulin stimulated glucose transport (which is activated within 2.5 min in isolated muscle cells and by 0.6 nM insulin in intact muscle in vitro). There is evidence that individual chemical species of DAG may provide a more specific signal. The DAG fraction from muscle was resolved into 5 peaks by gas chromatography. The species associated with these peaks were identified by comparing their retention times to those of standards. None of the species increased in response to 5 min incubation with insulin; 2 species increased after 10 min; 4 after 20 min. These changes paralleled insulin-stimulated increases in total DAG mass. To distinguish between insulin-stimulated phospholipase catalyzed hydrolysis of membrane phospholipids and insulin-stimulated de novo synthesis of DAG, phosphatidylcholine hydrolysis and glucose flux into lipids was measured. Insulin had no effect on the content of choline or phosphocholine, which suggests that phosphatidylcholine hydrolysis in muscle is not induced by insulin. Insulin did, however, promote glucose flux into DAG. Flux into total lipids also increased. These data suggest that the insulin-stimulated increment in total DAG mass in skeletal muscle is a downstream effect of insulin-stimulated glucose transport and metabolism and therefore appears not to be involved in mediating insulin-stimulated glucose transport.

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