Fertilization in crabs: IV. The fertilization potential consists of a sustained egg membrane hyperpolarization

AbstractThe electrophysiological properties of immature and mature oocytes of two crabs were analyzed. Growing immature oocytes of Carcinus maenas and fully grown immature oocytes of Maia squinado had essentially K+ dependent resting potentials, Em, of −61 ∓ 1 mV, n=19, and −67.3 ± 0.5 mV, n=68, respectively. Fully grown immature oocytes of Carcinus maenas showed an Em of −40 ± 1.5 mV, n=19, that was k+ and Cl− dependent. In mature oocytes of both species, the plasma membrane became exclusively permeable to cl− and the Em attained–41 ± 1 mV, n=49 and −34 ± 1.5 mV, n=27 for Carcinus maenas and Maia squinado, respectively. After in vitro insemination, a dramatic increase in egg membrane permeability to K+ was observed. This instantaneously caused a sustained hyperpolarization constituting, for these crabs, the fertilization potential. We observed that concurrently with this electrical response to fertilization, sperm reinitiated the oocyte meiotic maturation previously arrested at the first metaphase. The triggering mechanism of the fertilization potential as well as the possible occurrence of a physiological polyspermy are discussed.