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Influence of the toxicity of cryoprotective agents on the involvement of insulin-like growth factor-I receptor in surf clam (Spisula sachalinensis) larvae.

BACKGROUND
The signaling of insulin-like growth factor-I (IGF-I) is involved in the development, growth, reproduction and aging of vertebrates. However, few studies have investigated the involvement of IGF-I during states of extreme shock, such as those induced by potently toxic cryoprotective agents (CPAs) or low temperature conditions, in bivalves.


OBJECTIVE
We investigated the toxicity of CPAs and the potential relationship between larval viability and the IGF-I receptor (IGF-IR) after treatment with CPAs or freezing in surf clam (Spisula sachalinensis) larvae.


MATERIALS AND METHODS
The umbo larvae and different concentrations of CPAs (dimethyl sulfoxide, DMSO; ethylene glycol, EG) were used to investigate the toxicity of CPAs and the vitrification of surf clam larvae. The relationship between larval viability and the IGF-I receptor (IGF-IR) after treatment with CPAs or freezing was investigated using immunoblot analysis.


RESULTS
An increase in concentration greater than 4M DMSO was fatal in larvae; however, 5M EG combined with a mixture of CPAs had no harmful effects. Moreover, live larvae immersed in a 5M EG solution remained intact and maintained their normal shape and organs. However, even though the larvae survived the CPA toxicity test, none of the vitrified larvae survived. After immersion into CPAs and vitrification, 97-kDa IGF-IR ß-subunits could be detected in all larvae; but tyrosine phosphorylation of the intracellular β-subunits was detected only in the control and live groups.


CONCLUSION
IGF-IR was activated in the umbo larvae but not in dead surf clam larvae treated with CPA and frozen. Activation of IGF-IR has relevance to the umbo larval stage in live surf clams treated with CPAs.