Photopharmacological Modulation of Lipid-Gated TRPC Channels as a Strategy to Govern Neuronal Excitability

Abstract

Lipid-gated, TRPC channel isoforms 3, 6 and 7 are widely expressed in the brain. Although, cellular regulation and signalling functions of these proteins are well characterized in overexpressing systems, their role in native cells is incompletely understood. Recent evidence suggests a complex, inverse coupling between TRPC3 constitutive activity and hippocampal excitability, potentially involving promotion of a Ca2+-activated K+ conductance and afterhyperpolarization. Constitutive Ca2+ entry through TRPC3/6 might be enforced in a positive feedback loop, which involves linkage to K+ efflux and maintenance of electrochemical driving force. Nevertheless, acute suppression of hippocampal function in response to activation of TRPC3 channels via receptor-mediated pathways has not unambiguously been demonstrated. To identify the functional consequences of TRPC3 activation in hippocampus without interference of parallel signalling events from receptor/phospholipase C activation, we used derivatives of the novel, selective TRPC3/6 agonist GSK1702934A. GSK1702934A (10 µM) reversibly suppressed firing of primary cultures of murine hippocampal neurons, while, this effect was absent in hippocampal neurons lacking TRPC3/6 expression. Our results encouraged the design and generation of photochromic ligands for TRPC activation based on the GSK1702934A structure. Inclusion of an azobenzene moiety into ligands has successfully been used in photopharmacology of a variety of channels and receptors. An azobenzene-modified GSK1702934A derivative (optoGSK1) was found suitable for fast and reversible control of heterologously expressed TRPC3 and TRPC6 channels in HEK293 cells, and enable highly efficient, optical control of neuronal firing.