On the other hand: the stereoselectivity of drug action at ion channels.

Ion channels are pharmacological receptors with specific drug binding sites. These binding sites define specific structure-function relationships for the actions of drug classes. Interpretation of these structure-function relationships may be complex because of state-dependent drug-channel interactions. These state-dependent interactions determine affinity and access of drug to binding sites and may result in both quantitative and qualitative changes in structure-function relationships including stereoselectivity. A channel-active drug may exhibit antagonist or activator properties according to membrane potential and the stereoselectivity of interaction may also change with channel state.