Selective blocking effects of octanol on the various receptor responses of the ganglion cells of Aplysia

Abstract

Straight-chain n-alcohols are known to modulate some neuronal activities through direct binding to the ligand-gated ion channel. It has not been established, however, whether effects of alcohol on the receptor-induced current responses are due to a direct interaction with the agonist binding or are secondary to a perturbation of the membrane lipids. Octanol is one of the long chain alcohols and known to block the gap junction composed of two hemichannels. To compare the effects of octanol on receptor-induced responses of neurons, we applied 30-100 μM 1-octanol to Aplysia ganglion cells and tested with various receptors of ionotropic and metabotropic types using conventional voltage-clamp method. Application of octanol reduced significantly and reversibly nicotinic type of Na⁺-current response, another nicotinic type of Cl⁻-current response, GABA_A type of Cl⁻-current response, and dopamine-induced fast Na⁺-current response. In contrast, the same concentration of octanol did not reduce M₂ type of K⁺-current response, D₂ type of K⁺-current response, H₂ type of K⁺-current response, FMRFamide-induced K⁺-current response, D₁ type of Na⁺-currrent response, nor serotonin-induced Na⁺-currrent response. The former 4 types of receptors are known to be ionotropic and the latter 6 types to be metabotropic. Therefore, all types of ionotropic receptor responses examined so far were selectively inhibited by octanol. Keinetic analysis suggested that the inhibition of octanol of these responses is not caused by competition at their receptors. [J Physiol Sci. 2008;58 Suppl:S86]