Propanediol alters intracellular pH and developmental potential of mouse zygotes independently of volume change

Prior to treatment, mouse zygotes were incubated with acridine orange (AO) a fluorescent dye which fluoresces within a physiological pH range. The zygotes were then perifused with 1,2-propanediol (PROH) at rates of 0.18 mol/min, 0.36 mol/min and 1.0 mol/min and zygote volume and intracellular pH monitored. Zygotes perifused with phosphate-buffered saline maintained their initial volume and AO fluorescence. All of the zygotes exposed to PROH at a rate of 1 mol/min decreased in volume and lost their AO fluorescence by 10 min. The volume of the zygotes perifused at less than or equal to 0.36 mol/min was not altered. However, only 25% of the zygotes perifused at 0.36 mol/min maintained their fluorescence at 10 min and all lost their fluorescence by 15 min. At 0.18 mol/min 95% of the zygotes maintained their fluorescence at 10 min and 49% at 15 min. All of the PROH-exposed zygotes lost their fluorescence by 20 min. Although 2-cell development was not affected by 3.0 M PROH for 2.5 min, blastocyst development was reduced compared with controls (P less than 0.05). Longer exposures resulted in a significant decrease in both 2-cell and blastocyst development. These data demonstrate that a 2-7-min exposure to greater than or equal to 2.5 M PROH alters both the intracellular pH and developmental potential. Since these detrimental effects are independent of volume changes and therefore intracellular PROH concentrations, it is postulated that PROH mediates its toxic action by directly altering the cell membrane.