The M-current was first described approximately thirty years ago (Brown and Adams, 1980) and is now recognized as a key regulator of many neurological processes where it plays a dominant role in controlling excitability. In more recent years a number of small molecule modulators of the proteins that underlie the M- current (the Kv7 family of voltage-gated ion channels) have been reported. Both activators and inhibitors of the channel have been described and at least one activator, Retigabine, has progressed to late-stage clinical trials for the treatment of epilepsy. For years the mechanism that underlies the M-current's name (suppression of the current by agonist of Gq- coupled muscarinic acetylcholine receptors) remained mysterious. However, the work of Suh and Hille (2002) revealed that muscarinic receptor stimulated depletion of plasma membrane PIP2 was the likely mechanism governing muscarinic receptors suppression of the M-current. In subsequent years this mechanism of modulation of M-current has been of intense research interest. However, to date there have been no reports of easy-to-use;HTS-compatible assays to assess M-current modulation. Neither have there been any small- molecular tools reported that specifically target 7TM receptors'ability to modulate this critically important conductance. To address this problem we have initiated an effort to develop an HTS-compatible assay system and a suite of secondary assays to enable a screen focused on the discovery and characterization of small molecules that specifically modulate 7TM receptor suppression of M-current activity. Discovery of such tools will advance our understanding the role of 7TM receptors in modulating neuronal excitability via the M-current and may reveal novel therapeutic opportunities for Kv7 targets. Furthermore, with the growing appreciation of functional selectivity and context dependent pharmacology, there is an intense need for new 7TM receptor assay technologies that reflect known physiologically relevant effectors not presently addressed by standard assay technologies (e.g. intracellular calcium flux). The proposed M-current assay represents just such a novel assay system. In fact, though intracellular calcium flux is the most common cell-based functional assay technology for Gq-coupled muscarinic receptors, it appears that it is not the major signal transduction modality for muscarinic responses in some tissues including the neurons of the superior cervical ganglion (Hernandez et al, 2008) where muscarinic modulation of M-current is known to occur. Thus, not only does the proposed assay system represent an opportunity to discover novel and important small molecule probes, it also represents an important new mechanism for characterizing muscarinic receptor modulators.
The proposed research focuses on the development on novel technologies to enable the discovery of chemical modulators of the interactions between neuro-transmitter receptors and neuronal voltage-gated ion channels. These receptors and channels play key roles in nervous system function and are implicated in causing as well as treating numerous nervous system disorders. The proposed research will advance our knowledge regarding the role of these receptors and channels in normal and pathological processes with a focus on translating these into therapies for disease.
