A novel H+ permeability dominating intracellular pH in the early mouse embryo.
Most cell types are relatively impermeant to H+ and are able to regulate their intracellular pH by means of plasma membrane proteins, which transport H+ or bicarbonate across the membrane in response to perturbations of intracellular pH. Mouse preimplantation embryos at the 2-cell stage, however, do not appear to possess specific pH-regulatory mechanisms for relieving acidosis. They are, instead, highly permeable to H+, so that the intracellular pH in the acid and neutral range is determined by the electrochemical equilibrium of H+ across the plasma membrane. When intracellular pH is perturbed, the rate of the ensuing H+ flux across the plasma membrane is determined by the H+ electrochemical gradient: its dependence on external K+ concentration indicates probable dependence on membrane potential and the rate depends on the H+ concentration gradient across the membrane. The large permeability at the 2-cell stage is absent or greatly diminished in the trophectoderm of blastocysts, but still present in the inner cell mass. Thus, the permeability to H+ appears to be developmentally regulated.
Baltz
J M
JM
Laboratory of Human Reproduction and Reproductive Biology, Harvard Medical School, Boston, MA 02115.
Biggers
J D
JD
Lechene
C
C
D000818:Animals; D001755:Blastocyst / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D051379:Mice; D008815:Mice, Inbred Strains; D011188:Potassium / Q000378:metabolism; D017494:Proton Pumps / Q000502:physiology*
D017494:Proton Pumps; D011188:Potassium