Microcalorimetric measurement of production heat in isolated human adipocytes

A method for the quantitative measurement of heat production in isolated human adipocytes is described. Fat cells are isolated by collagenase treatment of biopsy specimens of adipose tissue, and heat production measured by microcalorimetry. The heat effect was constant for at least 4 h. Heat values increased with increasing pH (about 6% per 0.1 pH unit) and temperature (about 9% per degrees C at 37 degrees C). The apparent activation energy was calculated as 44 kJ/mol. Heat production was about 50% higher in cell suspensions containing glucose and insulin. Imprecision was about 6.5% (coefficient of variation) and sensitivity allowed measurements in samples containing 20-30 mg adipocyte lipid. Heat production in normal volunteers under standardized conditions (i.e. in Krebs-Ringer-bicarbonate buffer pH 7.4, at 37 degrees C and in the presence of 11 mmol/l glucose and 0.1 U/ml insulin) was 133 +/- 48 (mean +/- SD) microW/g adipocyte lipid weight, corresponding to 49 +/- 15 pW/cell. The technique seems of importance for the characterization of energy balance in the fat cell under normal and pathophysiological conditions.