INTRACELLULAR PH AND ITS REGULATION DURING FERTILIZATION AND EARLY EMBRYOGENESIS

Both in vivo and in vitro, mammalian embryos depend on their external environment for metabolites and for control and regulation of their internal composition, functions which are accomplished by transport proteins situated in their plasma membranes. The repertoire of transport mechanisms present in preimplantation embryos is beginning to be elucidated, and it is clear that embryonic transporters are in many cases unique. We are studying the set of transporters which regulate intracellular pH (pH(i)) in embryos. In sea urchins, it was known that activation of a pH(i) regulatory transporter is a crucial step in egg activation at fertilization. However, this does not appear to be the case in mammals. One pH(i) regulatory mechanism, the HCO3-/Cl- exchanger, which acts to counter alkalosis, is very active in the preimplantation embryo and is necessary for embryo development. In contrast, however, the otherwise ubiquitous mechanisms used to counter acidosis are apparently absent from the preimplantation embryo. The restriction of pH(i) regulation to the alkaline range may reflect the alkalinity of oviductal fluid.