Maturation of pig oocytes: observations on membrane potential.

The membrane-potential changes of pig oocytes during maturation are described. Cumulus-enclosed oocytes have a restingpotential of -41.81 ± 0.60 my; the removal of cumulus cells caused this potential to drop to -30.95 ± 0A3 my. Adding LHto the culture medium did not influence the potential of denuded oocytes but depolarized the potential of cumulus-enclosedoocytes to -32.90 ± 0.43 mY. FSH did not affect the membrane potential of denuded or cumulus-enclosed oocytes, but significantly reduced the amplitude of the depolarization induced by LH. The effect of gonadotropins on cultured granulosa cells wasalso investigated. Plated granulosa cells have a resting potential of -45.21 ± 0.72 mV, similar to that of cumulus-enclosed oocytes.As recorded in cumulus-enclosed oocytes, LII depolarized granulosa cell membrane potential (-30.33 ± 0.69 mY) and FSHreduced this effect. To evaluate if oocyte maturation in vivo is accompanied by membrane-potential depolarization, folliculargrowth and oocyte maturation were induced in 6 prepubertal gilts by using an eCG-hCG treatment. Twenty hours after thebeginning of oocyte maturation in vivo (induced by hCG), the membrane potential of the oocyte was depolarized to -28.84 ±1.01 mV, a value similar to that observed in vitro.These data indicate that both LB and FSH can influence the membrane potential of fofficular somatic cells and, consequently,that of the oocyte. The electrical coupling between somatic cell and oocyteoocyte. The electrical coupling between somatic cell and oocyte may represent a means by which the gonadotropinmessage is passed to the genninal cell by the somatic compartment.[...]