Pannexin-1 channels as facilitators of anandamide membrane transport

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The regulated movement of ions and small signaling molecules across the plasma membrane occurring through facilitated transport (channels and transporters) is a fundamental basis of cellular physiology. The close regulation of Ca2+ influx, for example, can determine the difference between normal and detrimental signaling. For several decades, my research program has been investigating mechanisms of facilitated transport and we having made several seminal discoveries. As an NSERC funded postdoc, I challenged the concept that ATP transport into the Golgi complex was mediated by a classical transporter. Rather I showed it was an ATP permeable anion channel. Since starting my own lab (in 2008), our research program has discovered that the ionotropic receptor for glutamate, the N-Methyl-D-Aspartate receptor (NMDAR) has a metabotropic signaling role in addition to its canonical ionotropic function. Thus, we continue to question the concept that channels are only channels, transporters are only transporters and that there is a clear distinction between ionotropic and metabotropic receptors. This Discovery grant proposal is focused on understanding the biophysics and neurophysiology of a novel facilitated transport role of the pannexin-1 (Panx1) channel. Panx1 is a non-selective ion and metabolite channel belonging to the gap junction superfamily. Importantly, it does not form intracellular gap junctions, rather it functions in plasma membranes as a bona fide channel, joining the intra- and extracellular spaces. Panx1 is best characterized as an ATP permeable channel that contributes to, and is regulated by, purinergic signaling pathways. Our previous NSERC grant focused on understanding the roles of Panx1 in purinergic signaling and immune responses. During this funding period we had several critical insights that have shaped the present proposal. For example, the mechanisms that regulate the opening of Panx1 channels are poorly characterized. Our understanding of the scope of the types of ions and molecules that can permeate the channels is limited, which restricts characterization of the likely diverse physiological roles of Panx1. In this regard, we made the important discovery that Panx1 can facilitate the transport of the signaling lipid, N-arachidonoylethanolamine (andandamide; AEA), a critical ligand in the endocannabinoid system. This Discovery grant will test the general hypothesis that Panx1 facilitates the transport of AEA to regulate endocannabinoid signaling in the brain. Our approach is unique and innovative, providing exciting opportunities for the training and development of highly qualified personnel. The work here will dramatically increase our understanding of the diverse biological roles of Panx1 through identifying a new and unique transport mechanism for anandamide and determining how this modulates neuronal function and circuit output.