Maturation and fertilization in Lottia gigantea oocytes: intracellular pH, Ca(2+), and electrophysiology.
Intracellular pH and Ca(2+) were measured with BCECF- and Calcium Green-dextran during maturation and fertilization of oocytes of the limpet Lottia gigantea. Maturation of oocytes from prophase to metaphase I of meiosis was induced in seawater adjusted to pH 9 with NH(4)OH. Intracellular pH rose during maturation induction, and maturation was also induced by microinjecting pH 8, but not pH 7, HEPES buffer. Intracellular Ca(2+) rose during NH(4)OH-induced maturation, but maturation was not inhibited when the increase was blocked by microinjection of BAPTA. When the metaphase I oocytes were fertilized(), there was an abrupt increase in intracellular Ca(2+), and activation (polar body formation) failed to occur in BAPTA-injected oocytes. Intracellular pH did not rise during fertilization. These observations show that maturation from prophase to metaphase I of meiosis is pH-dependent and activation of the metaphase I oocytes is Ca(2+)-dependent. A Ca(2+) action potential was present in both immature and mature oocytes but was more prominent in mature oocytes whose input resistance was higher. Fertilization produced a long-lasting (17-20 min) Na(+)-dependent fertilization potential with superimposed oscillations resembling Ca(2+) action potentials.
Gould
M C
MC
Instituto de Biología Celular y Molecular, Universidad Autónoma de Baja California, Ensenada 22800, BC., Mexico. mgould@faro.ens.uabc.mx
Stephano
J L
JL
Ortíz-Barrón
B J
BJ
Pérez-Quezada
I
I
D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004594:Electrophysiology; D005260:Female; D005306:Fertilization / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D008974:Mollusca / Q000502:physiology*; D009865:Oocytes / Q000502:physiology*; D012741:Sexual Maturation / Q000502:physiology*
D002118:Calcium