1719-Plat Stretch-Gated Ion Channels in Neuronal Mechanoreceptors Slav N. Bagriantsev, Eve R. Schneider, Evan O. Anderson, Jon Matson, Elena O. Gracheva. Cellular & Molecular Physiology, Yale University, New Haven, CT, USA. The sense of touch, or mechanosensitivity, is crucial for virtually all aspects of everyday life, yet among all the senses possessed by vertebrates, it remains least explored at the cellular and molecular levels. Key to touch sensitivity are neuronal mechanoreceptors, which constitute a minor group of neurons in the somatosensory ganglia of most vertebrates. The scarcity of neuronal mechanoreceptors coupled with the absence of unequivocal markers for their identification impedes progress in understanding the molecular mechanism of touch sensitivity. Towards this end, we developed a novel animal model - the trigeminal system of duck embryos. Ducks are tactile specialists capable of foraging by means of acute mechanosensitivity of the glabrous skin covering their bill. We found that in contrast to rodents and other vertebrates, the trigem- inal ganglia innervating duck head are dominated by mechanoreceptors instead of thermoreceptors and nociceptors. Electrophysiological analysis showed that duck trigeminal neurons have an augmented ability to convert touch into exci- tation, presumably due to the properties of the resident stretch-sensitive ion channels. We determined that a majority of duck trigeminal neurons express mechano-activated ion channels of the Piezo and Nav classes. We explored functional properties of these channels in vitro and inquired into their contribu- tion to mechanically activated excitatory current and action potential genera- tion in rapidly-adapting neuronal mechanoreceptors. Our data suggest a molecular mechanism underlying the sense of touch in the glabrous skin of vertebrates. 1720-Plat Biophysical Factors that Promote Mechanically-Induced Action Potentials in Neocortical and Hippocampal Pyramidal Neurons Yury A. Nikolaev 1 , Peter J. Dosen 1 , Derek R. Laver 1 , Dirk F. Van Helden 1 , Owen P. Hamill 2 . 1 School of Biomedical Sciences and Pharmacy, University of Newcastle, Callaghan, Australia, 2 Neuroscience, UTMB, Galveston, TX, USA. Pressure activation of single mechanosensitive (MS) cation channel currents can trigger action potentials in neocortical and hippocampal pyramidal neurons (Nikolaev et al., 2015). Here we describe several factors that underlie this powerful influence on neuronal activity. First, cell-attached patch recordings indicate the MS cation channels are located on the soma and therefore inject a depolarizing current close to the axonal initial segment/spike initiation zone (SIZ) where action potential threshold is lowest. Second, the rapid rise of the single MS channel current (< 50 ms) generates a rapid depolarizing (dV/dt) event that lowers spike threshold by favoring fast Na þ channel activa- tion over slower inactivation. Finally, with pressure activation the gating of the MS channel switches from single brief spontaneous openings (< 1 ms) to longer bursts of openings (~ 10 ms) during which a spike may be triggered by each stochastic opening within the burst. Thus, the combination of SIZ prox- imity and rapid, burst gating underlies the powerful influence of single MS channels on central neuronal activity. For comparison, whereas a unitary excit- atory post-synaptic current activated on a distal dendrite typically fails to trigger an action potential even when generating as much as 1000 fC charge transfer across the synaptic membrane, a single MS channel current that gener- ates less than 200 fC can trigger repetitive spiking. Nikolaev, Y.A. et al., Single mechanically-gated cation channel currents can trigger action potentials in neocortical and hippocampal pyramidal neurons (2015) Brain Research. 1608: 1-13. 1721-Plat Inflammatory Cytokine Il-1a Up-Regulates Piezo1 and Hyper-Sensitizes Chondrocytes to Compression Whasil Lee, Holly Leddy, Amy McNulty, Farshid Guilak, Wolfgang Liedtke. Duke University, Durham, NC, USA. In diarthrodial joints, chondrocyte mechanotransduction play a critical role in the maintenance of cartilage and in the pathogenesis of osteoarthritis (OA). The mechanistic understanding of chondrocyte mechanotransduction both in health and disease is essential for the rational prevention and treatment of joint diseases. We recently identified that injurious mechanical stress is transduced by the mechano-sensitive ion channels Piezo1 and Piezo2 in chondrocytes; blocking Piezo1/2 protected chondrocytes from injurious mechanical stress, suggesting a possible therapeutic benefit of this approach in cartilage injury or OA. Yet, little is known about how the OA joint environment may influence Piezo1/2-mediated mechanotransduction. We hypothesize that mechanotrans- duction of chondrocytes is altered by OA-related inflammatory stress, and that Piezo1/2 gene expression and function is altered in the context of OA. Here, we present new data in support of increased expression of Piezo1 in chon- drocytes under inflammatory conditions, associated with sensitization to me- chanical stimulation. We found that in the presence of pathophysiologically relevant concentrations of IL-1a, (1) the basal Ca 2þ concentration of articular chondrocytes was increased (~90nM), (2) mechanically activated Ca 2þ influx was increased (~50 nM by a compression force of 300nN), (3) Piezo1 mRNA levels increased (~2 fold). These findings suggest sensitization of chon- drocytes to mechanical cues via enhanced expression of Piezo1 channels. Also IL-1a treatment resulted in increased cell strain (~4%) at the same compressive load and attenuated cortical actin labeling, indicative of increased actin desta- bilization, whereas b-tubulin remained unaffected. These data indicate that IL-1a-exposed chondrocytes (and potentially their membranes) can deform more readily, thereby elevating gating probabilities of mechanosensitive ion channels. Our study shows that the OA-associated inflammatory cytokine IL-1a alters chondrocyte mechanotransduction, suggesting that chondrocytes’ mechanical hypersensitivity is due to upregulated Piezo1 mRNA expression caused by IL-1a-signaling. 1722-Plat Structural and Functional Characterizations of the Mechanosensitive Piezo Channel Bailong Xiao. Tsinghua University, Beijing, China. Piezo proteins are evolutionarily conserved and functionally diverse mechano- sensitive cation channels that play critical roles in various mechanotransduction processes. However, the overall structural architecture, ion permeation and gating mechanisms of Piezo channels have remained unknown. Here we deter- mine the cryo-electron microscopy structure of the full-length (2,547 amino acids) mouse Piezo1 (Piezo1) at a resolution of 4.8 A ˚ . Piezo1 forms a trimeric propeller-like structure (about 900 kilodalton), with the extracellular domains resembling three distal blades and a central cap. The transmembrane region has 14 apparently resolved segments per subunit. These segments form three peripheral wings and a central pore module that encloses a potential ion- conducting pore. The rather flexible extracellular blade domains are connected to the central intracellular domain by three long beam-like structures. This trimeric architecture suggests that Piezo1 may use its peripheral regions as force sensors to gate the central ion-conducting pore. Importantly, by character- izing the structurally revealed featured domains, we provide functional evi- dence to support this hypothesis. Taken together, these findings significantly advance our understanding of the structure-function relationship of this novel class of mechanosensitive cation channels. 1723-Plat Bending Piezo1: The Effect of Amphipaths on the Gating of a Mechanosen- sitive Channel Charles D. Cox 1 , Boris Martinac 1,2 . 1 Molecular Cardiology and Biophysics, Victor Chang Cardiac Research Institute, Sydney, Australia, 2 St Vincent’s Clinical School, University of New South Wales, Sydney, Australia. The PIEZO ion channel family represents an important and structurally novel class of molecular force transducer. These channels respond not only to mem- brane tension but also to shear stress induced by fluid flow. Here we investigate the effect of amphipathic compounds and asymmetric incorporation of conical and signaling lipids on PIEZO1 channels. One difficulty in studying such ef- fects is the fact that PIEZO1 activity ‘runs down’ in response to patch excision (inside-out patches). Recent data suggests this run down can be ameliorated by the addition of PIP2. We not only confirm this interesting finding but show that other amphipathic compounds and signaling lipids can also prevent this ‘run down’. For example, a physiologically important eicosanoid 20-HETE previ- ously shown to sensitize a member of the TRP channel family (TRPC6) to mechanical force increases the sensitivity of PIEZO1 channels in excised inside-out patches. This has potentially important implications for the physio- logical regulation of PIEZO1. Whether these effects are a result of local curva- ture or changes in line tension is unknown. However these results, in addition to our work with cytoskeletal deficient membrane blebs, support the proposal that Piezo1 channels are gated according to the force-from-lipids paradigm. Platform: Networks and Synthetic Biology 1724-Plat The Nonequilibrium Statistical Thermodynamics of Biological Cycles Jason A. Wagoner, Ken Dill. Laufer Center for Physical and Quantitative Biology, Stony Brook University, Stony Brook, NY, USA. Tuesday, March 1, 2016 349a