Journal of Lipid Research, Vol. 12, 104-111, January 1971
Copyright © 1971 by Lipid Research, Inc.

Intracellular accumulation of free fatty acids in isolated white adipose cells

A. Angel , K. S. Desai , and M. L. Halperin

Department of Medicine, University of Toronto, Toronto 181, Canada

A simple, rapid, and accurate method was developed for measuring intracellular FFA levels in isolated white adipose cells using sucrose-¹⁴C or inulin carboxyl-¹⁴C as nontransportable, nonutilizable markers of the extracellular space. Following incubation, medium and cells were separated by centrifugation and the infranatant medium was removed by aspiration. The volume of medium trapped between cells was determined by measuring the amount of sucrose-¹⁴C or inulin carboxyl-¹⁴C retained in the floating packed adipose cells. In this way the FFA content of the adipose cells could be corrected for contamination by FFA bound to extracellular albumin.

With this technique the initial events in hormone-activated lipolysis were studied under conditions of maximal and constant rates of triglyceride hydrolysis. The FFA content of isolated adipocytes of fed rats was 0.5 µmole/g cell lipid. On addition of norepinephrine in the presence of medium albumin, the concentration of intracellular FFA rapidly increased and reached a plateau at a concentration of 2-2.5 µmoles/g cell lipid. In the presence of medium albumin an initial lag in glycerol release occurred and this was attributed to partial hydrolysis of triglyceride with retention of lower glycerides. After 5 min of incubation FFA and glycerol output was constant. In the absence of medium albumin norepinephrine-stimulated lipolysis was reduced more than 90% and extracellular FFA release was not detected. Nevertheless, intracellular FFA accumulation was identical to that seen in the presence of albumin. The data suggest that most of this intracellular pool of FFA is bound to cytoplasmic constituents.

Supplementary key words lipolytic rates • hormone-stimulated lipolysis • intracellular FFA pools • fatty acid transport • fatty acid acceptors • sucrose space • fatty acid—glycerol balance

Submitted on March 30, 1970
Revised on August 3, 1970
Accepted on October 15, 1970

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