Purpose: We have previously reported that myristate, a saturated free fatty acid (FFA) with 14 carbons (C14), antagonizes volatile anesthetics in goldfish. The hydrophobicity and molecular configuration of FFAs may play an important role in the antagonizing effect. To examine their contribution, we investigated the antagonizing potencies of saturated and unsaturated long-chain FFAs in goldfish.
Methods: Saturated and monounsaturated FFAs of C14-18 were tested. We determined the anesthetic concentration producing a 50% effect (EC50) of isoflurane in the absence or presence of FFA by observing the escape reaction of goldfish against an electrical stimulus.
Results: All FFAs increased the EC50 of isoflurane dose-dependently compared with reactions in the absence of FFA ( P < 0.05). For saturated FFAs, the relationship between chain lengths and antagonizing potencies was not linear. C18 was the most effective and C16 was the least effective antagonist ( P < 0.05). Among unsaturated FFAs, C14 was the most effective antagonist ( P < 0.05). In a comparison of saturated and unsaturated FFAs, saturated C14 and C18 were more effective antagonists than unsaturated FFAs of the same carbon numbers ( P <<0.05).
Conclusion: The hydrophobicity of FFAs increases as the chain length increases. Therefore, our findings suggest that the antagonizing effect of long-chain FFAs in goldfish, in terms of their capacity to perturb the lipid membrane structure, may be determined not solely by their hydrophobicity but also by their molecular configuration.