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 in ternal composition, functions which are accomplished by transport prot eins situated in their plasma membranes. The repertoire of transport m echanisms present in preimplantation embryos is beginning to be elucid ated, and it is clear that embryonic transporters are in many cases un ique. We are studying the set of transporters which regulate intracell ular pH (pH(i)) in embryos. In sea urchins, it was known that activati on of a pH(i) regulatory transporter is a crucial step in egg activati on at fertilization. However, this does not appear to be the case in m ammals. One pH(i) regulatory mechanism, the HCO3-/Cl- exchanger, which acts to counter alkalosis, is very active in the preimplantation embr yo and is necessary for embryo development. In contrast, however, the otherwise ubiquitous mechanisms used to counter acidosis are apparentl y absent from the preimplantation embryo. The restriction of pH(i) reg ulation to the alkaline range may reflect the alkalinity of oviductal fluid.