Effect of different concentrations of potassium on pig embryos developing in vitro

The effects of varying the potassium concentration in Whitten's medium on the development of pig embryos in vitro was investigated. Osmolality was maintained by adjusting the NaCl concentration. In Expt I, 209 one-cell to early blastocyst stage embryos were individually cultured in 50 microliters microdrops of glucose-free Whitten's medium containing 0.4% (w/v) BSA and 1.5, 3.0, 6.0 or 12.0 mmol potassium l-1. The percentages of embryos undergoing blastocoel formation and expansion for each cell stage evaluated did not differ (P > 0.10) among the various concentrations of potassium. However, more four-cell embryos commenced hatching in 3.0 mmol potassium l-1 (53%) than in 1.5 mmol potassium l-1 (16%) (P < 0.05) and 12.0 mmol potassium l-1 (24%) (P < 0.10). The time required for embryos to develop blastocoels, expand and initiate hatching was not affected (P > 0.10) by the concentration of potassium in the medium. However, blastocoel formation by one- to two-cell embryos was delayed (P < 0.05) in medium with 1.5 mmol potassium l-1. In Expt 2, 89 four-cell embryos were cultured in medium containing 6.0 or 24.0 mmol potassium l-1. No differences (P > 0.10) were observed in the percentages of embryos undergoing blastocoel formation, expansion and hatching or in the time required to develop to these stages. The number of cells in embryos recovered at 96 h was greater (P < 0.05) in medium containing 6.0 compared with 24.0 mmol potassium l-1 (32.9 +/- 1.7 versus 26.9 +/- 2.1, respectively). These results demonstrate that pig embryos are tolerant to a wide range of potassium concentrations when the osmolality of the medium is maintained by adjusting the NaCl concentration. These results also suggest that limitations in development due to culture conditions are not due to inappropriate concentrations of this ion.