Experiments have been performed to investigate the use of coral skeletons as bone graft substitutes. Skeletal fragments of different coral genera were implanted into cortical and spongy bone defects and used to bridge transcortical resections in the femur. The implant site was monitored for up to 18 months. Radiographically, both cortical and spongy bone defects were at least partially filled by new bone after 8 weeks while the implants underwent continuous resorption. Coral resorption and replacement by new tissue was also observed in the transcortical resections. The process of resorption was attributed to the enzymatic attack, especially carboanhydrase. This was confirmed by experiments in which dogs were implanted with coral in transcortical resections and treated daily with acetazolamide, a carboanhydrase inhibitor; the absorption appeared delayed and the resections failed to heal.

The use of coral as a bone graft substitute.

Previous studies showed that natural coral implanted into bone tissue was gradually resorbed and progressively replaced by newly formed bone. The objectives of this study were to compare the fate of two Madreporian corals, Porites and Acropora, after implantation during 1 and 2 months into sheep and pig long bones. These materials are identical in composition (CaCo3) but differ in volume (49 +/- 2%, 12 +/- 4%, respectively) and mean size (250 vs. 500 microns) of porosities. The non-decalcified histological slices were observed under light microscopy. Implant resorption and new bone formation were quantified through an automatic image analysis system. Quantitative results showed that the larger the porosity volume, the greater was the coral resorption as well as the new bone apposition. Large differences were found between the two animal species. Histological findings were identical to those previously reported: implants were resorbed and progressively replaced by newly formed bone. Coral was found to be an osteoconductive biomaterial which acted as a scaffold for a direct osteoblastic apposition and consequently could be an interesting alternative to bone auto-, allo-, or xenografts.

Comparison of coral resorption and bone apposition with two natural corals of different porosities.

Carbonate Precipitation and Dissolution: Its Relevance to Fossil Preservation

Behavioural components of prey selection by dogwhelks, Nucella lapillus (L.), feeding on mussels, Mytilus edulis L., in the laboratory

The whelk, Buccinum undatum tries to attack all bivalves in the same way: It orients itself so that the front edge of the foot lies in contact with the edge of the valves of the prey; when the bivalve opens, the whelk suddenly inserts its lip between the valves thus preventing their closing. Buccinum may introduce its proboscis through the narrow slit or the valves may in some cases be wedged further open. Cardium edule is quickly devoured by this technique but a number of other cardiids as well as Nuculana pernula, Venus ovata, Spisula subtruncata and S. elliptica leap away when attacked. Pectinids swim away when touched by the foot of Buccinum. Species such as Mytilus edulis, Modiolus modiolus, Astarte montagui, Arctica islandica, and Venus striatula keep closed so long that Buccinum usually gives up and crawls away. Mya arenaria is buried so deep that it cannot be reached by the whelk. Stomach contents of specimens from the Oresund show a high occurrence of Modiolus, but it is concluded that t...

Observations on Buccinum Undatum L. attacking bivalves and on prey responses, with a short review on attack methods of other prosobranchs

In land gastropods, calcium is precipitated in the shell, in connective calcium cells which are largely distributed through the whole connective tissue, in epithelial calcium cells of the digestive gland, and in the calcium gland cells of the skin and the mantle collar. Calcium is taken up from the external medium by food and by absorption through the sole skin. To adapt to terrestrial life, these animals have to eliminate appreciable amounts of calcium for their protection and their reproduction. During the egg laying period, a calcium flux occurs through the epithelium of the reproductive tract in order to supply the egg shell and the egg fluids. This egg calcium is taken up by the embryo. The maintenance of a positive calcium balance between its uptake and the loss is due to an important reservoir of easily mobilizable calcium in the form of calcium carbonate. This reservoir consists of the connective calcium cells which are constantly able to accumulate or release calcium as long as calcium is locally available or required. The epithelial calcium cells of the digestive gland are loaded with calcium phosphate; they are not a major calcium storage compartment, but have an essential function in detoxification. All of the calcium movement occurring across cell membranes and through epithelia concerns only calcium ions. All calcium movement can be regarded either as on-off systems or as reversible systems, both of which are certainly controlled by complex processes

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Calcium Dynamics in Land Gastropods

Measurement of carbonic anhydrase (CA) activity in homogenates of accessory boring organs of the muricid gastropod, Purpura lapillus , by Meldrum and Roughton's manometric method showed that CA is always present in boring as well as in inactive ABOs, but in variable amounts. Tests by the same method on whole ABOs in an isotonic solution were negative, proving that CA remains intracellularly.

Experiments in vivo on inhibition and activation demonstrated clearly that CA is responsible for demineralization of the valves of lamellibranchs by Purpura: (a) at low concentrations of Diamox, partial inhibition of the enzymeoccurred, that is, the number of complete holes decreased or disappeared and etchings increased; and at higher concentrations full inhibition took place. Inhibition is reversed when snails are replaced in normal sea water; (b) action of pure CO2 or mixtures of CO2 and O2 accelerated boring: in the optimal mixture, three times more boreholes were produced by snails than in the controls, and in about half the time. Under these conditions the reaction catalyzed by CA goes to the right with hydration of CO2 and is accompanied by release of H+ ions; in the presence of an increased concentration of CO2, the reaction is intensified and results in an additional release of H+ ions. Consequently, destruction of CaCO3 by the ABO of Purpura in sea water enriched with CO2 is accelerated.

To identify the nature of the exchanged ion, we tested the effect of NaCl and KC1 on the boring mechanism in vivo by increasing the amount of these salts in the seawater of snails with prey. In this case augmentation of the boring activity was noticed. These results suggest that the boring activity is accompanied by complex ionic exchanges.

Shell-Boring Mechanism of the Gastropod, Purpura (Thaïs) lapillus: a Physiological Demonstration of the Role of Carbonic Anhydrase in the Dissolution of CaCO3

Jean Fournié

Papers

Calcium Dynamics in Land Gastropods

Shell-Boring Mechanism of the Gastropod, Purpura (Thaïs) lapillus: a Physiological Demonstration of the Role of Carbonic Anhydrase in the Dissolution of CaCO3