Metabolism of glucose by rat pancreatic islets and kidney: comparison of membrane preparations with intact tissue.
BACKGROUND
Insulin secretion in the pancreatic islet of Langerhans is closely related to glucose oxidation. Our previous membrane preparations from the islet of Langerhans and kidney contained Na+/K+ ATPase. Although ATP is a modulator of insulin release, we have not demonstrated that membranes contain glycolytic enzymes.


OBJECTIVE
To compare glucose oxidation in intact islets of Langerhans with that seen in islet membranes, and to examine renal tissue because of easy access to this tissue and because our previous work contrasted islets and kidney Na+/K+ ATPase activity.


METHODS
To examine whether membrane preparations of both islets and kidney contain glycolytic activity, we designed an apparatus that determines tissue glucose oxidation rates by measuring 14CO2 production from 14C-1-D-glucose. In contrast to previous methods, O2 was supplied and pH was maintained in physiologic ranges throughout the incubations.


RESULTS
At 5.5 mM glucose, oxidation was linear over 2 hours in intact islets and kidney. Islets produced approximately twice the 14CO2 as kidney, or 1000 nmol CO2/mg protein/hour. Membranes oxidized glucose at less than 10% of the rates observed with intact tissue. Concentration dependency was linear from 0-11.0 mM glucose; however, at 16.5 mM, oxidation decreased to less than half of that seen at 11.0 mM.


CONCLUSIONS
Our "membrane" preparations contain some glycolytic activity but are unlikely to contribute significant amounts of ATP in most studies of ATP hydrolysis, such as that seen in experiments that measure ATPase activity.
Song
Moon K
MK
Diabetes Research Laboratory, Medical and Research Services, West LA VA Medical Center, 11301 Wilshire Boulevard, Los Angeles, CA 90073, U.S.A.
Levin
Seymour R
SR
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D002245:Carbon Dioxide / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002469:Cell Separation / Q000379:methods; D005947:Glucose / Q000378:metabolism*; D007515:Islets of Langerhans / Q000166:cytology / Q000378:metabolism*; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D051381:Rats
D002245:Carbon Dioxide; D000251:Adenosine Triphosphatases; D005947:Glucose