title: Characterization of mechanisms for Ca2+ and HCO3(-)/CO3(2-) acquisition for shell formation in embryos of the freshwater common pond snail Lymnaea stagnalis.
abstract: The freshwater common pond snail Lymnaea stagnalis produces embryos that complete direct development, hatching as shell-bearing individuals within 10 days despite relatively low ambient calcium and carbonate availability. This development is impaired by removal of ambient total calcium but not by removal of bicarbonate and/or carbonate. In this study we utilized pharmacological agents to target possible acquisition pathways for both Ca(2+) and accumulation of carbonate in post-metamorphic, shell-laying embryos. Using whole egg mass flux measurements and ion-specific microelectrode analytical techniques, we have demonstrated that carbonic anhydrase-catalyzed hydration of CO(2) is central in the acquisition of both shell-forming ions because it provides the hydrogen ions for an electrogenic vacuolar-type H(+)-ATPase that fuels the uptake of Ca(2+) via voltage-dependent Ca(2+) channels and possibly an electrogenic Ca(2+)/1H(+) exchanger. Additionally, CO(2) hydration provides an endogenous source of HCO(3)(-). Thus, hydration of endogenous CO(2) forms HCO(3)(-) for calcification while hydrogen ions are excreted, contributing to continued Ca(2+) uptake, as well as creating favorable alkaline internal conditions for calcification. The connections between Ca(2+) and HCO(3)(-) acquisition mechanisms that we describe here provide new insight into this efficient, embryonic calcification in freshwater.
authors.affiliation: University of Miami, Rosenstiel School of Marine and Atmospheric Science, Division of Marine Biology and Fisheries, 4600 Rickenbacker Causeway, Miami, FL 33149, USA.
authors.forename: Sue C
authors.initials: SC
authors.lastname: Ebanks
authors.forename: Michael J
authors.initials: MJ
authors.lastname: O'Donnell
authors.forename: Martin
authors.initials: M
authors.lastname: Grosell
mesh_terms: D000468:Alkalies; D000825:Animal Structures / Q000196:embryology* / Q000378:metabolism; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000187:drug effects / Q000378:metabolism*; D005618:Fresh Water; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007811:Lanthanum / Q000494:pharmacology; D008195:Lymnaea / Q000187:drug effects / Q000196:embryology* / Q000378:metabolism*; D008839:Microelectrodes; D008954:Models, Biological; D009543:Nifedipine / Q000494:pharmacology; D017186:Titrimetry; D014700:Verapamil / Q000494:pharmacology
chemical_list: D000468:Alkalies; D001639:Bicarbonates; C028521:lanthanum chloride; D007811:Lanthanum; D014700:Verapamil; D009543:Nifedipine; D002118:Calcium