Ionic Currents in Lymnaea stagnalis Eggs During Maturation Divisions and First Mitotic Cell Cycle

Abstract

The eggs of the mollusc Lymnaea stagnalis generate weak extracellular ionic currents, which have been mapped from oviposition through first cleavage. Throughout this period the current is inward in the animal hemisphere, with highest density at the animal pole, and outward in the vegetal hemisphere, with highest density at the vegetal pole. Peak current densities are measured at the time of first and second polar body formation. During anaphase and telophase of the first mitotic cell cycle, the outward current at the vegetal pole reaches its minimum density and its direction is reversed in most eggs, whereas the inward current at the animal pole gradually increases. This coincides with the segregation of the so-called animal pole plasm to the animal pole (Raven, 1970). The organic calcium channel blockers diltiazem and D600 cause abnormal maturation division(s) and/or first cleavage. At the same time they reduce and eventually abolish the associated ionic currents. These results suggest the existence of a cell-cycle correlated, calcium-dependent component of ionic currents in Lymnaea eggs.

Cell cycle-related fluctuations in transcellular ionic currents and plasma membrane Ca2+/Mg2+ ATPase activity during early cleavages of Lymnaea stagnalis embryos

“…The polar pattern of currents observed during the first four mitotic divisions agrees with the polar pattern measured in the same species during meiosis (Zivkovic and Dohmen 1989). A similar current pattern, showing an animal-vegetal polarity, has also been observed in Xenopus oocytes before maturation (Robinson 1979).…”

“…Details concerning maintenance of Lymnaea stagnalis snails under laboratory conditions, as well as obtaining and handling of eggs and embryos for vibrating probe measurements and Ca2+/Mg z+ ATPase enzyme cytochemistry, have been described previously (Dohmen et al 1986;Zivkovic and Dohmen 1989;Zivkovic et al 1990). …”

“…The magnitude and pattern of the ion currents were measured using the extracellular vibrating probe (Jaffe and Nuccitelli 1974) as described previously (Zivkovic and Dohmen 1989). We used a one-dimensional vibrating probe system with metal electrodes provided with a 15-25 gm platinum tip, which were vibrated with amplitudes of 15-30 lain (Scheffey 1988).…”

“…1986;Zivkovic and Dohmen 1989). The aim of the present study was to document exactly the correlation between temporal changes in the pattern of ionic currents and a particular phase of the cell cycle.…”

Cell lineage in molluscan development

“…These currents have also been detected in molluscan eggs viz. in Lymnaea stagnalis (Zivkovic and Dohmen, 1989;Zivkovic et al, 1991a,b) and in Bithynia terztaculata (Zivkovic, 1990;Zivkovic and Dohmen, 1991). The highest densities of inward and outward current are measured at the animal or vegetal pole of the egg, indicating that ion transport systems are either accumulated, or preferentially activated, at the poles.…”