Starfish oocytes of A. pectinifera reveal marked differences in sperm-induced electrical and intracellular calcium changes during oocyte maturation and at fertilization.

Abstract

Although changes in membrane potential and intracellular Ca2+ (Cai ) during fertilization in starfish oocytes have been known for long time, little is known precisely about how and what kind of channels are involved during oocyte maturation and in fertilization, and how the mechanisms of changes in Cai in oocytes develop during oocyte maturation. Since in starfish, oocyte maturation-inducing hormone, 1-methyladenine (1MA) is well known, we took advantage of it to investigate the developmental process of channel-function and changes in Cai in three different developmental stages using 1MA. Sperm-induced membrane current at voltage clamp and changes in Cai in starfish oocytes, Asterina pectinifera, were examined in stages of immature, partly mature (a state in 15-20 min after sufficient concentration, 1 µM of 1MA addition, or 30-40 min exposure to subthreshold concentration of 1MA), and mature oocytes (MO). We found some immature and many partly MOs showed fluctuating responses in membrane current, membrane potential, and corresponding changes in Cai , which are distinct from those in MOs. The responses in immature and partly MOs indicate physiologically characteristic responses of insufficient changes in Cai and its corresponding electrical responses at the partial developmental stage during maturation. Our data should shed light on the mechanism of egg activation and oocyte maturation in terms of examining membrane current and corresponding changes in Cai .