LOW INTRACELLULAR PH IS INVOLVED IN THE EARLY EMBRYONIC DEATH OF DDK MOUSE EGGS FERTILIZED BY ALIEN SPERM

Intracellular pH was measured in normal 8-cell stage mouse embryos and in embryos from a cross between DDK females and C3H males. DDK/C3H em bryos display the DDK syndrome and spontaneously begin to decompact to ward the late 16-cell stage. Ultimately, 90% fail to form blastocysts. Normal embryos have a resting intracellular pH close to neutrality. I n DDK/C3H embryos a substantial proportion (46%) has an intracellular pH below 6.7. An equivalent proportion of DDK/C3H embryos was found pr eviously to show slow communication through gap junctions at the 8-cel l stage. This is probably a consequence of low intracellular pH. In no rmal embryos the weak acid, butyric acid, decreased intracellular pH a nd slowed the transfer of Lucifer Yellow through gap junctions. Normal embryos treated with butyrate for between 1 and 6 hr beginning at the 8-cell stage and cultured for 24 hr, reproduced the DDK/C3H phenotype . After 48 hr some butyrate treated embryos recovered, while others re mained as decompacted morulae. Treatment of control and DDK/C3H 8-cell stage embryos with dibutyryl cyclic AMP or forskolin, which win incre ase intracellular cyclic AMP, speeded gap junctional communication. Fo rskolin treatment prevented expression of the DDK syndrome in DDK/C3H embryos, although the rescue was transient and the syndrome returned w hen forskolin was removed. The finding that the DDK syndrome is manife sted as low intracellular pH may provide clues to the molecular basis of the defect. (C) 1994 Wiley-Liss, Inc.