INTRACELLULAR DIVALENT-CATION HOMEOSTASIS AND DEVELOPMENTAL COMPETENCE IN THE HAMSTER PREIMPLANTATION EMBRYO

The intracellular magnesium and calcium ion concentrations of in vivo- developed 2-cell hamster embryos were measured using ratiometric fluor ometry. Intracellular magnesium and calcium ion concentrations were fo und to be 0.369 +/- 0.011 mM and 129.3 +/- 7.5 nM respectively. Cultur e of 1-cell hamster embryos for 24 hr to the 2cell stage in control me dium containing 0.5 mM magnesium and 2.0 mM calcium resulted in approx imately a threefold increase to 343.5 +/- 8.0 nM in intracellular calc ium ion concen tration, while magnesium ion levels were not altered (0 .355 +/- 0.007 mM). Increasing medium magnesium concentrations to 2.0 mM significantly increased intracellular magnesium ion concentrations of cultured 2-cell embryos with a concomitant reduction in intracellul ar calcium ion concentrations. Furthermore, increasing the medium magn esium concentration to 2.0 mM significantly increased development of 1 -cell embryos collected at either 3 or 9 hr post-egg activation to the morula/blastocyst and blastocyst stages. Resultant blastocysts had an increased total cell number and increased development of the inner ce ll mass. Most important, however, culture with 2.0 mM magnesium increa sed the fetal potential of cultured 1-cells twofold. Therefore, becaus e highest rates of development were observed in a medium that resulted in reduced intracellular calcium ion concentrations, it appears that altered calcium homeostasis is associated with impaired developmental competence of 1-cell embryos in culture. Mol. Reprod. Dev. 50:443-450, 1998. (C) 1998 Wiley-Liss, Inc.