Effect of potassium concentration, type of protein supplement, and embryo density on mouse preimplantation development in vitro

Mouse preimplantation embryos were used to test the effects of three culture parameters on development of 2-cell stage embryos to the late morula stage (40 to 43 hours of culture, 65 to 80 hours after fertilization): (1) concentration of potassium (K)—0.6 mM, 1.4 mM, and 6.0 mM; (2) type of protein supplement, bovine serum albumin (BSA), and bovine serum immunoglobulins (BSIG); and (3) number of embryos (2 or 20) cultured per 10- to 12-µl drop of T6 culture medium under paraffin oil. Cell number per embryo of cultured late morulae was compared with that of same-age embryos developing in vivo. The developmental rate to late morula stage with 20 embryos per drop of medium was media containing 0.6- and 1.4-mM K, 0.15% BSA, 0.15% BSIG > medium containing 1.4-mM K, 0.3% BSA > all media containing 6.0-mM K (P < 0.01 comparing media containing 0.6- or 1.4-mM K with media containing 6.0-mM K). For a given medium, developmental rate was significantly slower for 2 embryos per drop than for 20 embryos per drop of medium with those media containing either 0.3% BSA (for all concentrations of K tested) or 6.0-mM K (for 0.3% BSA and for 0.15% BSA + 0.15% BSIG). Finally, cell number per embryo was: in vivo-developed embryos > medium containing 1.4-mM K, 0.15% BSA, 0.15% BSIG >> 6.0- or 1.4-mM K, 0.3% BSA. These data suggest that developmental rate and embryo cell number are enhanced by media containing a reduced concentration of K in combination with a mixture of serum proteins and by culturing several embryos together.