Calcium-mediated transduction of the hormonal message in meiosis reinitiation of starfish oocytes: modulation following injection of cholera toxin and cAMP-dependent protein kinase

Injections of the regulatory subunit of type I cAMP-dependent protein kinase, of the heat-stable inhibitor protein of cAMP-dependent protein kinase and of calmodulin have no effect on meiosis reinitiation. Drugs, including theophylline, caffeine and procaine, which have been shown previously to inhibit 1-methyladenine (1-MeAde)-induced Ca²⁺ release, both in living starfish oocytes and from plasma membrane-rich fractions obtained from isolated cortices, inhibit meiosis reinitiation when added before—but not after—the end of the hormone-dependent period (period when presence of the hormone in the medium is required for meiosis to occur). In the same conditions, theophylline suppresses 1-MeAde-induced stimulation of protein phosphorylation. Injection of cholera toxin subunit A increases oocyte sensitivity to 1-MeAde. Catalytic subunit of cAMP-dependent protein kinase (C) inhibits meiosis reinitiation when injected before the end of the hormone-dependent period. Oocytes can be released from inhibition due to C injection by raising 1-Me-Ade concentration. These findings support the view that Ca²⁺ release occurs until transduction of the hormonal message (i.e., its intramembrane transfer) has been completed and show that protein phosphorylation remains under plasma membrane control until that time. They also suggest that transduction of the hormonal message might be modulated by intracellular cAMP and membrane phosphorylation, although cAMP content does not change following 1-MeAde addition.