Manipulation of cytokinesis affects polar ionic current around the egg of Lymnaea stagnalis

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Abstract
The fertilized egg of the mollusc Lymnaea stagnalis generates a polarized current pattern as measured with the vibrating probe. Here we investigated the basis of these polar ionic currents. Ionic currents were measured around eggs during the second meiotic division after interference with cytokinesis. Cytokinesis was either displaced by centrifugation or inhibited with cytochalasin or nocodazole. Furthermore, ectopic constrictions were induced with lectin treatment. It appeared that the inward current of the animal pole can be displaced by centrifugation and remains associated with the position of the meiotic apparatus. The influence of the meiotic apparatus on the polar current pattern seems to be directly related to membrane constrictions rather than to karyokinesis. This was demonstrated by a change in current density after induction of an ectopic constriction at the vegetal pole and by the abolishment of currents after cytochalasin treatment. Since the location of the outward current was not sensitive to centrifugation, it may be concluded that the vegetal outward current depends upon properties of the vegetal cortex. On the basis of these results, we conclude that the Lymnaea egg generates two types of ionic currents during the second meiotic division. The first is an inward current activated at the site of membrane constrictions. The second is an outward current associated with the vegetal cortex.