3 Osmotic and Ionic Regulation in Teleost Eggs and Larvae
1988; Academic Press; Linguagem: Inglês
10.1016/s1546-5098(08)60200-9
ISSN1557-8011
Autores Tópico(s)Reproductive biology and impacts on aquatic species
ResumoThis chapter discusses the osmotic and ionic regulation in teleost eggs and larvae. The teleost egg differs in one major respect from those of the polychaetes, echinoderms, and amphibians, in having a micropyle in the outer egg membrane. In the sea-urchin egg, at the instant of sperm contact with the plasma membrane, evidence supports the occurrence of three consecutive electrical events. The initial depolarization appears to be sperm-dependent and it seems to trigger an action potential dependent on external Na+ and Ca2+ and suggests that a calcium-carrying potential-gated membrane channel is primarily responsible. The latter phase of the action potential overlaps the initial phase of activation potential and results from increased Na+ conductance by the membrane. Repolarization at the end of the activation potential appears to be the result of a resequestering of Ca2+ and a pH-dependent increase in K+ conductance. The total fertilization potential may then involve gated membrane channels and Ca2+, K+, Na+, and H+ ions. Three important functional aspects of a membrane include its water permeability, the transfer of ions, and its electrical properties. Various techniques have been used, refined, and redefined for measuring the movement of particles across a membrane. An examination of permeation characteristics at various stages of embryonic development suggests that mature oocytes have a highly permeable plasma membrane.
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