Barnea candida

Abstract: Barnea caridida oocytes release acid (135 pmole H+/oocyte) upon fertilization After artificial activation by an excess of KCl, germinal vesicle breakdown (GVBD) occurs normally and a quite similar, but not identical, acid release is recorded (110 pmole H+/oocyte) KCl activation of Barnea oocytes is completely inhibited in 100 mM sodium-acetate sea water at pH 65 and fertilization does not result in activation when the oocytes are transferred after one minute into 100 mM sodium-acetate sea water at pH 63 When D–600, a calcium transmembrane fluxes inhibitor, is added 20 seconds after fertilization, GVBD is inhibited but a normal acid release is recorded The presence of at least 10 mM sodium ions in the external medium is required for 100% activation of these oocytes by an excess of KCl These results suggest that while an intracellular pH increase may be a requisite for GVBD, this can not be a sufficient condition to trigger it unless a calcium influx is allowed to occur Moreover, the acid release does not result from a Ca++-H+ exchange transport but appears more likely to be due to a Na+-H* exchange as it has been demontrated in sea urchin eggs

Abstract: Fertilization is accompanied by changes in the structure of the egg cytoplasm (cf. Rothschild, 1958; Raven, 1961). At the level of fine structure such changes have mainly been studied in some marine invertebrates with small eggs that can easily be fertilized in vitro (Pasteels & de Harven, 1963; Schafer, 1966). Vertebrate eggs are less favourable in this respect, but electron microscope studies have been made on eggs of mammals (Flechon, 1966; Zamboni & Mastroianni, 1966; Zamboni, Mishell, Bell & Baca, 1966) and Xenopus (van Gansen, 1966). Changes generally observed soon after fertilization include the formation of polysomes or an increase in their number, a hypertrophy of the Golgi complexes, and the appearance of granulated endoplasmic reticulum and annulate lamellae. Afzelius (1957) observed the dispersal of mitochondria in fertilized sea-urchin eggs. Pasteels & de Harven (1963) reported that the structure and distribution of cytoplasmic organelles in eggs of the bivalve mollusc, Barnea Candida , are not altered by fertilization.

Abstract: Barnea candida oocytes, submitted to D-600 (100 microM) 15-20 seconds after insemination in order to inhibit Ca++ uptake but not acid release, fail to exhibit germinal vesicle breakdown (GVBD) whereas penetrated spermatozoa are able to decondense normally. Oocytes transferred in 100 mM Na-acetate seawater at pH 6.3, 1 minute after insemination, in order to inhibit acid release, fail to undergo GVBD and sperm nuclear decondensation. Upon return of these oocytes to normal seawater and treatment with an excess of KCl, they exhibit GVBD and decondensed sperm nuclei are seen within their cytoplasm. These results show that sperm nuclear decondensation does not require GVBD or Ca++ uptake but may be related to an intracellular pH increase.