Calcium fluxes in hydrozoan embryos depend, in part, on exocytosis and fluid phase endocytosis. |
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Authors: | E B Ridgway G Freeman |
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Institution: | Friday Harbor Laboratories, University of Washington, USA. |
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Abstract: | In the hydrozoan Phialidium gregarium, the constitutive calcium influx of cleavage stage embryos in sea water is 1.96 +/- 0.75 x 10(-15) moles/embryo/minute. Treating embryos with 227 mM KCl in seawater briefly increases the calcium influx more than 100-fold, to 3.9 x 10(-13) mol/embryo/min. About 62% of the KCl-induced calcium influx is due to calcium flowing through voltage-sensitive calcium channels. This causes a marked intracellular calcium transient and secretion of intracellular vesicles. The other component (approximately 38%) of the calcium influx occurs via fluid phase endocytosis of the extracellular medium (detected using extracellular 3H-sucrose). KCl-treatment of 45Ca loaded embryos induces a 45Ca efflux which can reach peak fractional rates of 0.98/min, during which 55-75% (mean 66%) of the total 45Ca is lost. The KCl-induced calcium efflux is due, in part, to secretion because loaded 3H-sucrose is effluxed simultaneously. This pathway may be important for the calcium efflux necessary for long-term calcium homeostasis in cells. |
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