Abstract
Several lines of evidence suggest that ionic messengers are primary agents in the metabolic derepression which occurs at fertilisation. The derepression at fertilisation or partheno-genetic activation of the sea urchin egg occurs in two main phases. The first phase, which triggers the early events of fertilisation, is mediated by transitory increase of intracellular free calcium1β3. The second, which triggers the late events of fertilisation, is mediated by a rise in the intracellular pH (refs 4β6). The transition from the early events of fertilisation of sea urchin eggs to the late events requires a minimal concentration of sodium in the external medium7. External Na+ is required for the acid efflux which follows fertilisation8. Na+ requirement and the acid efflux have been correlated in a hypothesis which proposes that internal protons are exchanged for external Na+ (refs 8, 9). By using pH-sensitive microelectrodes, we have examined the relationship between external Na+ and internal pH more closely. We demonstrate here that the increase of the intracellular pH following egg activation does require external Na+. However, the relative insensitivity of the alkalisation of the egg cytoplasm to large reductions of external Na+ is evidence against the NaβH exchange hypothesis.
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Shen, S., Steinhardt, R. Intracellular pH and the sodium requirement at fertilisation. Nature 282, 87β89 (1979). https://doi.org/10.1038/282087a0
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DOI: https://doi.org/10.1038/282087a0
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