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

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.