Reciprocal Changes in Calcification of the Gastrolith and Cuticle During the Molt Cycle of the Red Claw CrayfishCherax quadricarinatus

Abstract

Mobilization of calcium during the molt cycle from the cuticle to transient calcium deposits is widely spread in crustaceans. The dynamics of calcium transport to transient calcium deposits called gastroliths and to the cuticle over the course of the molt cycle were studied in the crayfish Cherax quadricarinatus. In this species, calcium was deposited in the gastroliths during premolt and transported back to the cuticle during postmolt, shown by digital X-ray radiograph analysis. The predominant mineral in the crayfish is amorphous calcium carbonate embedded in an organic matrix composed mainly of chitin. Scanning electron micrographs of the cuticle during premolt showed that the endocuticle and parts of the exocuticle were the source of most of the labile calcium, while the epicuticle did not undergo degradation and remained mineralized throughout the molt cycle. The gastroliths are made of concentric layers of amorphous calcium carbonate intercalated between chitinous lamella. Measurements of pH and calcium levels during gastrolith deposition showed that calcium concentrations in the gastroliths, stomach, and muscle were about the same (10 to 11 mmol l(-1)). On the other hand, pH varied greatly, from 8.7+/-0.15 in the gastrolith cavity through 7.6+/-0.2 in muscle to 6.9+/-0.5 in the stomach.

Solubility and bioavailability of stabilized amorphous calcium carbonate

“…(18) Based on our findings, phosphoproteins in this remarkable organism were found to be capable of stabilizing one of the least stable salts in nature, ACC. (17) The unique physicochemical properties of ACC enable the crayfish to store large quantities of calcium in transient storage sites and, when needed, to rapidly and efficiently reabsorb calcium through the intestinal epithelia.…”

“…In an attempt to further increase the similarity of synthetically produced ACC to the ACC produced by the crayfish, embedded in a chitin matrix and serving as our biologic inspiration, (17,18) chitosan, the commonly used deacetylated derivative of chitin, was added during the synthesis of ACC-C. Chitosan is also suggested to increase intestinal absorption of macromolecules such as octreotide, insulin, and low-molecular-weight heparin (LMWH). (45)(46)(47) It is proposed that polycations such as chitosan increase molecule absorption by enhancing permeability through tight junctions in the intestine.…”

“…(16,17) When needed, the thermodynamic instability of ACC can be exploited to dissolve calcium and allow for fast transport of this ion across the intestinal epithelium and into the bloodstream. (18,19) The bioavailability of calcium in both humans and rats has been suggested to be governed by factors such as dose quantity, the nature of the chelating molecule, solubility of the salt, and the hormonal state of the receiving subject. (1) Furthermore, calcium in humans is absorbed by at least two and possibly three different pathways along the gastrointestinal tract.…”

Molt and gastroliths inAustropotamobius pallipes(Lereboullet, 1858)

“…In particular, both height (GH) and diameter (GD) were surveyed only for the right gastrolith (since they are symmetric structures), and the left one of the same specimen was prepared for a scanning electron microscope (SEM) by rinsing in water and drying in air. Then dry samples were dipped in liquid N 2 , broken, and gold-sputtered according to Shechter et al (2008), in order to count the number of the gastrolith layers (GL), i.e. concentric layers of amorphous calcium carbonate intercalated between chitinous lamellae (Shechter et al, 2008).…”

“…Then dry samples were dipped in liquid N 2 , broken, and gold-sputtered according to Shechter et al (2008), in order to count the number of the gastrolith layers (GL), i.e. concentric layers of amorphous calcium carbonate intercalated between chitinous lamellae (Shechter et al, 2008). Finally, captivity observations were made, using animals collected from the same study area with the aim of detecting the exact molting time.…”