THE ORGANIZATION OF THE CORTICAL ENDOPLASMIC-RETICULUM IN XENOPUS EGGS DEPENDS ON INTRACELLULAR PH - ARTIFACT OF FIXATION OR NOT

The cortical endoplasmic reticulum (CER), which develops and becomes organized during oocyte maturation in Xenopus laevis (anuran amphibians), has been thought to be essential for the propagation of the activating signal at the time of fertilization, possibly by regulating intracellular Ca2+ (Ca2+i) (Charbonneau and Grey, Dev. Biol. 102, 90-97, 1984). The present paper demonstrates that changing intracellular pH (pHi) has an influence on the structure and organization of the CER in unactivated Xenopus eggs. Acidifying the egg cytoplasm from its normal value, pH 7.5, to about 6.8, with CO2, produced a dramatic increase in the proportion of the CER being in the form of a continuous and well-developed network. On the other hand, alkalinizing the egg cytoplasm from 7.5 to about 8.2, with NH4Cl, induced a general disruption and vesicularization of the CER. These effects of pHi on a Ca2+i-regulating system are discussed, taking into account possible artefacts generated during fixation. © 1990 Elsevier Scientific Publishers Ireland, Ltd. All rights reserved.