Acid Release during Activation of Barnea candida (Mollusca, Pelecypoda) Oocytes. (acid release/oocyte activation/Barnea candida)

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Abstract
B. candida oocytes release acid (1.35 pmol/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 (1.10 pmol H+/oocyte). KCl activation of Barnea oocytes is completely inhibited in 100 mM sodium-acetate sea water at pH 6.5 and fertilization does not result in activation when the oocytes are transferred after 1 min into 100 mM sodium-acetate sea water at pH 6.3. When D-600, a Ca transmembrane fluxes inhibitor, is added 20 s after fertilization, GVBD is inhibited but a normal acid release is recorded. The presence of at least 10 mM Na ions in the external medium is required for 100% activation of these oocytes by an excess of KCl. While an intracellular pH increase may be a requisite for GVBD, this can not be a sufficient condition to trigger it unless a Ca influx is allowed to occur. The acid release does not result from a Ca2+-H+ exchange transport but is probably due to a Na+-H+ exchange as demonstrated in sea urchin eggs.