O-039 Mitochondrial ATP generation in mammalian eggs and Ca2+ signaling

Abstract textIn metaphase II arrested mammalian oocytes (eggs) and cleavage stage embryos the mitochondria are responsible for nearly all ATP production because glycolysis is inactivated. Luciferase assays show that ATP levels in eggs are strictly dependent upon pyruvate and fatty acid oxidation. The level of ATP in eggs appears to be maximal in conventional medium because the addition of extra mitochondrial substrates to eggs does not increase cytosolic ATP. The only clear elevation of ATP is seen at fertilization and is associated with sperm induced Ca2+ oscillations. Our recent findings suggest that the level of ATP modulates events at fertilization.At fertilization, the egg is activated by sperm derived PLCzeta which triggers a series of Ca2+ oscillations, with each Ca2+ release event causes by inositol trisphosphate (InsP3). Previous studies have shown that mouse eggs are more sensitive to PLCzeta, and generate higher frequency Ca2+ oscillations, than human eggs. Mouse eggs also generate Ca2+ oscillations and activate in response to Sr2+ that directly stimulates InsP3 receptors. In contrast, human eggs that contain the same type of InsP3 receptors do not generate Ca2+ oscillations in response to Sr2+.The difference in sensitivity of Ca2+ release between species can be explained by the fact that mouse eggs are about ten times more sensitive to InsP3 than human eggs. The reason for this difference appears to be due to ATP. The ATP level in unfertilized mouse eggs is about ...
Source: Human Reproduction - Category: Reproduction Medicine Source Type: research