Evidence for the involvement of carbonic anhydrase and urease in calcium carbonate formation in the gravity-sensing organ of Aplysia californica

To better understand the mechanisms that could modulate the formation of otoconia, calcium carbonate granules in the inner ear of vertebrate species, we examined statoconia formation in the gravity-sensing organ, the statocyst, of the gastropod mollusk Aplysia californica using an in vitro organ cul...

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Bibliographic Details
Published in:Calcified tissue international 1997-09, Vol.61 (3), p.247-255
Main Authors: Pedrozo, H. A., Schwartz, Z., Dean, D. D., Harrison, J. L., Campbell, J. W., Wiederhold, M. L., Boyan, B. D.
Format: Article
Language:English
Subjects:
Animals
Aplysia - enzymology
Aplysia - metabolism
Aplysia - ultrastructure
Calcium
Calcium Carbonate - metabolism
Carbonic Anhydrases - metabolism
Enzymes
Gravitation
Gravity
Homeostasis
Hydrogen-Ion Concentration
In Vitro Techniques
Life Sciences (General)
Protein synthesis
Sense Organs - metabolism
Space life sciences
Urease - metabolism
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Summary:To better understand the mechanisms that could modulate the formation of otoconia, calcium carbonate granules in the inner ear of vertebrate species, we examined statoconia formation in the gravity-sensing organ, the statocyst, of the gastropod mollusk Aplysia californica using an in vitro organ culture model. We determined the type of calcium carbonate present in the statoconia and investigated the role of carbonic anhydrase (CA) and urease in regulating statocyst pH as well as the role of protein synthesis and urease in statoconia production and homeostasis in vitro. The type of mineral present in statoconia was found to be aragonitic calcium carbonate. When the CA inhibitor, acetazolamide (AZ), was added to cultures of statocysts, the pH initially (30 min) increased and then decreased. The urease inhibitor, acetohydroxamic acid (AHA), decreased statocyst pH. Simultaneous addition of AZ and AHA caused a decrease in pH. Inhibition of urease activity also reduced total statoconia number, but had no effect on statoconia volume. Inhibition of protein synthesis reduced statoconia production and increased statoconia volume. In a previous study, inhibition of CA was shown to decrease statoconia production. Taken together, these data show that urease and CA play a role in regulating statocyst pH and the formation and maintenance of statoconia. CA produces carbonate ion for calcium carbonate formation and urease neutralizes the acid formed due to CA action, by production of ammonia.
ISSN:0171-967X
1432-0827
DOI:10.1007/s002239900330