Fuel Choices by Human Platelets in Human Plasma

Despite the fact that homogeneous preparations of isolated cells are now being used very effectively to study a range of important biochemical questions, it is still not known what combination of fuels and energy-producing pathways is used by cells when offered the complex mixture characteristic of plasma or extracellular fluid. We have developed an in vitro system whereby highly purified and functional human platelets are incubated in human plasma that has been minimally modified from its native state. The concentration of platelets and fuels, and the complexity of fuels in the incubation are similar to those in vivo. The preparation thus represents a reasonable approximation of the physiological condition, considering the complex nature of the system being studied. Measurements carried out simultaneously during the incubation are rates of oxygen consumption, lactate production and fuel oxidation. The data allow the calculation of total ATP turnover, and contributions to this turnover by lactate production and the oxidation of individual fuels. Lactate production accounts for 24% of the ATP turnover. The oxidation of glucose and 3-hydroxybutyrate each account for under 5%, palmitate for 21%, oleate for 7% and acetate for 9%, leaving 32% of the ATP turnover as yet unaccounted for. The results confirm some previous measurements in the literature, but show that data collected under non-physiological experimental conditions can be misleading.