1‐Methyladenine induction of oocyte (starfish) maturation: Inhibition by procaine and its pH dependency

Abstract

AbstractFully grown oocytes of starfish (Asterias forbesi) are normally arrested in the dictyate stage of meiosis within the ovary. Reinitiation of meiotic maturation in these oocytes appears to be induced as a result of the interaction of 1‐methyladenine (1‐MA) with the oocyte surface. The objective of this investigation was to determine whether procaine, a membrane active pharmacological agent, alters the ability of 1‐MA to induce oocyte maturation. Procaine (0–2 mM) at pH 8.3 inhibited 1‐MA induced maturation in a dose dependent manner; inhibition of maturation was seen only when the oocytes were incubated with procaine prior to the addition of 1‐MA. The inhibitory effect of procaine was reversible as indicated by the observation that oocytes which failed to mature in seawater containing 1‐MA (1 μg/ml) and 1 or 2 mM procaine at pH 8.3 subsequently underwent maturation after washing the procaine out and incubation with 1‐MA. Procaine inhibition of oocyte maturation was dependent on pH of the seawater; this inhibitory action of procaine decreased as pH decreased from 8.5–6.0. In seawater at pH 7, procaine (2 mM) reduced the biological activity of 1‐MA to approximately 0.1 of its potency; at pH 8.3 procaine completely blocked 1‐MA induction of oocyte maturation. The amount of 1‐MA bound or incorporated into the oocytes, as measured by the radioactivity in oocytes following incubation in seawater containing 3H‐1 methyladenine, is reduced to 10% of control by 2.0 mM procaine. Taken together, the data suggests that procaine inhibits oocyte maturation by limiting the amount of hormone on or in the oocyte and that this effect is pH dependent.