Proton-independent activation of acid-sensing ion channel ASIC3 by alkaloid lindoldhamine from Laurus nobilis
BACKGROUND AND PURPOSE
Acid-sensing ion channels (ASICs) play an important role in synaptic plasticity and learning, as well as in nociception and mechanosensation. ASICs are involved in pain and in neurological and psychiatric diseases, but their therapeutic potential is limited by the lack of ligands activating them at physiological pH.
We extracted, purified and determined the structure of a bisbenzylisoquinoline alkaloid, lindoldhamine, (LIN) from laurel leaves. Its effect on ASIC3 channels were characterized, using two-electrode voltage-clamp electrophysiological recordings from Xenopus laevis oocytes.
At pH 7.4 or higher, LIN activated a sustained, proton-independent, current through rat and human ASIC3 channels, but not rat ASIC1a or ASIC2a channels. LIN also potentiated proton-induced transient currents and promoted recovery from desensitization in human, but not rat, ASIC3 channels.
CONCLUSIONS AND IMPLICATIONS
We describe a novel ASIC subtype-specific agonist LIN, which induced proton-independent activation of human and rat ASIC3 channels at physiological pH. LIN also acts as a positive allosteric modulator of human, but not rat, ASIC3 channels. This unique, species-selective, ligand of ASIC3, opens new avenues in studies of ASIC structure and function, as well as providing new approaches to drug design.