Fig. 1. ICl,swell activity in mouse oocytes and embryos. (A) Magnitudes (mean ± s.e.m.) of whole-cell currents measured at +50 mV at various developmental stages of oocytes and embryos first in isotonic (240 mOsM; white bars, see key), then in hypotonic (180 mOsM; black bars), and then in hypotonic solution after the introduction of DIDS (180+DIDS; gray bars). Data are shown for oocytes in prophase of first meiosis (GV) and metaphase of second meiosis (O), as well as for 1-cell (1c), 2-cell (2c), 4-cell (4c), and 8-cell (8c) cleavage-stage embryos, morulae (M) and blastocysts (B). The time since ovulation was induced is indicated below as hours post-hCG (GV oocytes were obtained before hCG would have been administered; for embryos, fertilization occurred at about 12 hours post-hCG). Mean increase in total oocyte/embryo diameter in 180 mOsM medium at the time of the reported measurements (black bars) was 17-20%, except for oocytes and 1-cell embryos where it was 13-15%. Number of replicates (number of oocytes or embryos) is indicated above bars. Significant difference in current before swelling or after DIDS introduction relative to current at maximal swelling is indicated by asterisks (***P<0.001; **P<0.01; ns, P>0.05; ND, not determined). (B) Examples of currents elicited by swelling in ovulated (second meiotic metaphase) oocyte, 1-cell embryo, and 8-cell embryo (as indicated at bottom). At the top are traces of current over time, with each spike representing currents elicited by a voltage ramp (see text). The superimposed solid line shows total oocyte or embryo diameter relative to initial diameter before swelling (axis at right). The variable lag time between introduction of hypotonic solution and the initiation of cell swelling evident here was routinely observed. This probably arises from the time needed for the hypotonic solution to wash out the more dense and viscous 240 mOsM solution. External solutions are indicated by bars with same shadings as in the key in A. The 8-cell embryo shown here was one of the few to exhibit any significant ICl,swell. At the bottom are current versus voltage plots for the same oocyte/embryos (solid line, before swelling; dotted line, after swelling; dashed line, after DIDS). Voltage has been corrected for 10 mV liquid junction potential (LJP).
