Heat conduction microcalorimetry of overall metabolism in rabbit alveolar macrophages in monolayers and in suspensions

A technique has been developed for studying the overall metabolism in small numbers of cells in monolayers and in suspensions by measuring the heat exchange rate with a thermopile heat-conduction microcalorimeter. The system was tested with alveolar macrophages from rabbits, and heat flux-time curves could be monitored from numbers of cells as low as 0.05 . 10(6). The metabolic activity was found to be unchanged or to decrease very slowly over a period of 20 h. In a conventional cell medium, without the addition of serum, a mean heat flux value of 19.4 (S.D. 3.2) pW. cell-1 (37 degrees C, pH = 7.4) was obtained for alveolar macrophages in monolayers. The corresponding value for cells in the same medium, with the addition of 20% homologous rabbit serum, was 27.0 (S.D. 2.0). We suggest that this calorimetric method can be used as a short-term cytotoxic test for measuring potentially toxic agents in our environment; this test can involve alveolar macrophages of either animal or human origin. In such an assay, the cells should be used in monolayers, and suspensions should be avoided. We found that when alveolar macrophages were used in suspension, the metabolic activity, measured as heat flux, was dependent on cell concentration, even at values as low as 0.2. 10(6) cells per ml.