Timothy G. Hales - US grants

The Cys-loop receptor family includes the nicotinic acetylcholine receptor (nAChR) and the serotonin type 3 receptor (5-HT3R). Cys-loop receptors are neurotransmitter-activated ion channels participating in neurotransmission in the nervous system. They are targets of drugs for treating disorders from nausea to anxiety. Mutations in Cys-loop receptors can lead to diseases including epilepsy. Neurotransmitter binding opens the ion channel by initiating the movement of the second transmembrane (TM2) domain of each of the channel's five subunits. In the conventional view of the channel an outer vestibule narrows to the rate-limiting region within the membrane where the gate is located; the pore then opens into the cytoplasm. Thus, in this scheme, determinants of ion conduction reside exclusively in TM2. However, recent evidence renders this textbook view of Cys-loop receptors obsolete: First, cryoelectron microscopy revealed that the nAChR has narrow "portals" at the cytoplasmic interfaces of each subunit; Second, mutagenesis of these regions in the 5-HT3R influences ion conduction. These findings necessitate revision of the model for the ion permeation pathway. Thus this project addresses a fundamental question in neuroscience: does conduction through ion channels involve cytoplasmic elements? Data from this laboratory demonstrate that intracellular regions of 5-HT¬3Rs affect all aspects of ion conduction: conductance, voltage-dependence and ionic selectivity. This study will identify the mechanisms involved, creating a new model for Cys-loop receptor function. A key objective of the study is to continue to develop a Cys-loop receptor database accessible to physicians, researchers and educators. Thus this project will enhance the infrastructure for research and education at The George Washington University and beyond. Undergraduate students spearhead the development of the Cys-loop receptor database.