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 e xamine the effect of osmolarity on human placental mitochondria. Mitoc hondria from human term placenta were isolated by differential centrif ugation, and incubated in the presence of different concentrations of sucrose or KCI, to modify the osmolarity of the media. Rat liver mitoc hondria were used as control. The parameters studied were: respiration rate, adenine nucleotide hydrolysis, calcium transport, membrane pote ntial, 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. Al though the ATPase activity was enhanced in the absence of a respirator y substrate, no change in ATP hydrolysis due to osmolarity was observe d. 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 w ith KCl showed aggregation, whereas dispersed mitochondria were observ ed with sucrose. This study showed that sucrose-induced changes in osm olarity, does not modify metabolic and transport properties of human p lacental mitochondria, whereas KCl-induced osmolarity changes does aff ect these functions.