The effect of osmolarity on human placental mitochondria function

Human placental explants survive large changes in osmolarity, but the mechanism for this property is unknown. The goal of this work was to examine the effect of osmolarity on human placental mitochondria. Mitochondria from human term placenta were isolated by differential centrifugation, and incubated in the presence of different concentrations of sucrose or KCl, to modify the osmolarity of the media. Rat liver mitochondria were used as control. The parameters studied were: respiration rate, adenine nucleotide hydrolysis, calcium transport, membrane potential, and mitochondrial morphology. Stimulation of the mitochondrial respiration rate and an increase in Ca2+ transport was observed in the presence of K+. With sucrose, Ca2+ transport showed a complex kinetic behavior, whereas the respiratory control was slightly diminished. Although the ATPase activity was enhanced in the absence of a respiratory substrate, no change in ATP hydrolysis due to osmolarity was observed. ADP hydrolysis was inhibited by a high K+ concentration, but not by sucrose. The membrane potential was not modified by osmolarity, even in the absence of sucrose or K+ in the medium. Mitochondria isolated with KCl showed aggregation, whereas dispersed mitochondria were observed with sucrose. This study showed that sucrose-induced changes in osmolarity, does not modify metabolic and transport properties of human placental mitochondria, whereas KCl-induced osmolarity changes does affect these functions.