Progesterone-induced down-regulation of an electrogenic Na+, K+-ATPase during the first meiotic division in amphibian oocytes

Abstract

Progesterone initiates the resumption of the meiotic divisions in the amphibian oocyte. Depolarization of the Rama pipiens oocyte plasma membrane begins 6-10 hr after exposure to progesterone (1-2 hr before nuclear breakdown). The oocyte cytoplasm becomes essentially isopotential with the medium by the end of the first meiotic division (20-22 hr). Voltage-clamp studies indicate that the depolarization coincides with the disappearance of an electrogenic Na+, K+-pump, and other electrophysiological studies indicate a decrease in both K+ and Cl- conductances of the oocyte plasma membrane. Measurement of [3H]-ouabain binding to the plasma-vitelline membrane complex indicates that there are high-affinity (Kd = 4.2 x 10-8M), K+-sensitive ouabain-binding sites on the unstimulated (prophase-arrest) oocyte and that ouabain binding virtually disappears during membrane depolarization. [3H]-Leucine incorporation into the plasma-vitelline membrane complex increased ninefold during depolarization with no significant change in uptake or incorporation into cytoplasmic proteins or acid soluble pool(s). This together with previous findings suggest that progesterone acts at a translational level to produce a cytoplasmic factor(s) that down-regulates the membrane Na+, K+-ATPase and alters the ion permeability and transport properties of both nuclear and plasma membranes.

Ion currents modulating oocyte maturation in animals

“…In Ambystoma, an interplay between the fluctuation of sodium currents and decreased hydrogen ion conductance was described during the progesterone-induced oocyte maturation [Baud and Barish 1984]. These findings further support the hypothesis that progesterone induced GVBD via a down-regulation of the membrane sodium-potassium ATPase and, hence, influence the ion permeability and transport properties of both nuclear and plasma membranes [Weinstein et al 1982].…”

Progesterone binding to the α1-subunit of the Na/K-ATPase on the cell surface: Insights from computational modeling

“…The present study uses: 1) our published data on progesterone-ouabain competition for a binding site on the external surface of isolated plasma membranes from Rana pipiens oocytes [8,12], 2) site-directed mutagenesis studies of ouabain binding to sheep and human Na/KATPase α1-subunits by other investigators (e.g. [13]), and 3) the known amino acid sequence of α1-subunit isoforms from protein data banks.…”

“…The outer surface of the amphibian oocyte plasma membrane is known to have binding sites for both progesterone [15] and ouabain [12]. Table 2 summarizes the dissociation constants, binding capacity and estimated molecular weights of the ouabain binding component in plasma-vitelline membranes from prophase-arrested (unstimulated) R. pipiens oocytes.…”

“…Ouabain binding to the oocyte plasma membrane was measured after incubation of prophasearrested oocytes (denuded of follicle cells) in [ 3 H]ouabain, followed by the rapid manual isolation of plasma membranes [12]. Scatchard analysis of [ 3 H]ouabain binding to the isolated plasma membrane indicates the presence of at least two components: a K + -sensitive, high affinity site (K d = 3 × 10 −8 M) linked to inhibition of the pump, and a low affinity site (K d = 2 × 10 −6 M) which does not appear to be associated with transport inhibition [12].…”

“…Scatchard analysis of [ 3 H]ouabain binding to the isolated plasma membrane indicates the presence of at least two components: a K + -sensitive, high affinity site (K d = 3 × 10 −8 M) linked to inhibition of the pump, and a low affinity site (K d = 2 × 10 −6 M) which does not appear to be associated with transport inhibition [12]. The binding capacity for the low-affinity ouabain site and the progesterone site are comparable.…”