Direct Free Fatty Acid Storage in Different Sized Adipocytes from the Same Depot

Objective: Human adipocytes take up free fatty acids (FFA) directly from the circulation, even at times of high lipolytic activity. Whether these processes occurs simultaneously within the same cells or are partitioned between different cells, for example large and small cells, is unknown. Methods: The direct FFA storage in subcutaneous fat in 13 adults were measured using a continuous infusion of [U-C-13] palmitate and a bolus of [1-C-14] palmitate followed 30 min later by abdominal and femoral adipose biopsies. The adipocytes were isolated by digestion procedures and separated into small, medium and large populations by differential floatation. Results: Populations of adipocytes were isolated that were statistically and clinically (similar to 3 fold different) in size. Adipocyte lipid SA was not different between small, medium and large cells, therefore, FFA storage per unit lipid was not different. However, FFA storage rates were significantly (two to four times) greater per cell in large than small cells (P < 0.005). In summary, relative to lipid content, FFA storage rates are not different in large and small adipocytes, however, large cells have greater storage rates per cell. Conclusions: This suggests that the processes of FFA release and storage are taking place simultaneously in adipocytes.