title: Calcium fluxes in hydrozoan embryos depend, in part, on exocytosis and fluid phase endocytosis.
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.
authors.affiliation: Friday Harbor Laboratories, University of Washington, USA.
authors.forename: E B
authors.initials: EB
authors.lastname: Ridgway
authors.forename: G
authors.initials: G
authors.lastname: Freeman
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004705:Endocytosis / Q000502:physiology*; D005089:Exocytosis / Q000502:physiology*; D006829:Hydra / Q000196:embryology*; D010477:Perfusion / Q000295:instrumentation; D011189:Potassium Chloride / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism; D013997:Time Factors
chemical_list: D013395:Sucrose; D011189:Potassium Chloride; D002118:Calcium