Ion Channel Transporter Interactions

Project Summary Voltage-gated potassium (Kv) channels, essential for cellular electrical activity, are generated by tetramers of pore-forming α subunits, often in complexes with other, non-pore-forming β subunits and other protein classes. Sodium-coupled solute transporters provide a mechanism for transport of water-soluble ions, neurotransmitters, vitamins, sugars and other small molecules across cell membranes and against the electrochemical gradient. In prior award cycles we discovered that Kv channels form physical complexes with sodium-coupled solute transporters and we defined multiple modes of co-regulation in these “chansporter” complexes, establishing a new class of cellular signaling hub. Concomitant with this work, we discovered a range of novel small-molecule modulators of Kv channels and chansporter complexes, including synthetic compounds and plant metabolites, some with therapeutic potential. In this latest cycle, we propose to pursue both these fields of study, focusing primarily on the Kv1 (KCNA) and Kv7 (KCNQ) Kv channel families, disruption of which causes disorders as diverse as ataxia, cardiac arrhythmia, diabetes, achlorhydria, hypothyroidism, and epilepsy, and the transporters with which they interact. We will build on our prior work and preliminary data that include novel chansporter complexes, novel modes of Kv channel chemosensing in chansporter complexes, and screening results revealing abundant new Kv channel modulators from plants. We have established two new, unpublished transgenic rodent lines for this project that will facilitate study of new therapeutic approaches to treat Episodic Ataxia 1 (EA1) (a mouse model), and of the precise roles in vivo of KCNQ5 and KCNQ5-transporter complexes (a Kcnq5 knockout rat line). We use a highly integrated approach to investigate the molecular mechanistic bases for channel and chansporter biology and pathophysiology, drawing from our long experience in studying molecular basis of biology and disease in multiple tissues, cellular electrophysiology, transport and radioligand assays, transcriptomics, various imaging modalities, structure-function studies, and biochemical techniques. In the next five years, we aim to address several critical knowledge gaps, pursuing the following novel research directions: (1) Molecular mechanistic studies of new and known channel-transporter complexes to dissect novel forms of co-regulation and signaling; (2) Channel/transporter-active small molecule discovery from plants, drawing from our completed dual-target screen of 1444 plant extracts; (3) elucidation of novel roles for KCNQ5 in the vasculature and brain; (4) in vivo testing of the first compounds known to directly rescue EA1-linked Kv1.1 sequence variants. Our overarching goals are to uncover new chansporter complexes and their roles in vivo, enhance understanding of Kv channel biology, and discover novel and therapeutically relevant channel/transporter-targeted small molecules.