PubMed · 1186860
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L Dybas. 1975-10-30. Cell within a cell or a circulating cell pair.. https://doi.org/10.1038/257790a0
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In order to test the involvement of Ca2+ in maturation and activation of eggs, we have treated Chaetopterus eggs with ionophore A23187 and quercetin, an inhibitor of Ca2+-dependent ATPase. Ionophore A23187 induced rapid germinal vesicle breakdown (GVBD) and activated eggs as evidence by fertilization envelope elevation at a wide range of concentrations. Higher concentrations of A23187 induced GVBD in Ca2+-free artificial sea water, demonstrating the independence of GVBD in Chaetopterus from external Ca2+. At high concentrations of ionophore, eggs became ameboid and underwent the initial phases of differentiation without cleavage. Low concentrations of quercetin induced GVBD with or without external CA2+. This treatment did not activate eggs, but allowed them to be fertilized and undergo some development. The results of these experiments indicate 1) that Ca2+ fluxes regulate GVBD and activation in Chaetopterus, 2) that these fluxes can be internally generated, and 3) that Ca2+ sequestration by Ca2+-dependent ATPase may have a role in maintaining the intact germinal vesicle.
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The muscular system in the posterior sucker of Branchiobdella pentodonta Whit. has circular, longitudinal and radial fibers. In the anterior sucker, which has circular and longitudinal fibers, the muscle system is scarce. Concentric fibers are found around the mouth. In both suckers the glandular element form voluminous complexes secreting mucus for attachment to the substrate. Suckers show neuromuscular junctions and three distinct types of neuroglandular junctions: one with typical neurosecretory granules, one with larger neurosecretory granules produced by cells located at the origin of the segmental nerves, and one with presynaptic vesicles. The second type is peculiar to the posterior sucker. A comparison is made between suckers of Branchiobdella and those of leeches.