Polar lobe formation and cytokinesis in fertilized eggs of Ilyanassa obsoleta: III. Large bleb formation caused by Sr2+, ionophores X537A and A23187, and compound 4880 |
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Authors: | Gary W Conrad Susan E Davis |
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Institution: | 1. Division of Biology, Kansas State University, Manhattan, Kansas 66506, USA;2. Mount Desert Island Biological Laboratory, Salsbury Cove, Maine 04672 USA |
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Abstract: | Fertilized eggs of Ilyanassa obsoleta form a protuberance which resembles a normal polar lobe when injected with Sr2+ or Ca2+ by microiontophoresis. Eggs also form a lobe-like protuberance when exposed to any of three drugs: compound , ionophore X537A, and ionophore A23187. Protuberances form more quickly and at lower drug concentrations if additional exogenous Ca2+ is added, whereas higher concentrations of Mg2+ do not have such an effect. When eggs are exposed to these drugs in Ca2+-, Mg2+-“free” seawater, with or without 10 mM EDTA, the eggs are still able to undergo extensive shape changes and form protuberances. Drug-induced shape changes are prevented by cytochalasin B, but will still occur in the presence of colchicine. Approximately 75% of Ilyanassa eggs are capable of forming and resorbing their third polar lobe and undergoing cytokinesis in Ca2+-, Mg2+-“free” artificial seawater (even containing 10 mM EDTA), solutions which by atomic absorption spectroscopy are shown to contain low concentrations of Ca2+ (3–5 μM) and Mg2+ (1.0–3.5 μM). The data suggest that if Ca2+ is required for normal polar lobe formation and cytokinesis, it is derived from intracellular sources or is required in only very low exogenous concentrations (i.e., less than 10?2 μM free Ca2+, in the presence of 10 mM EDTA). |
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