Biophysical Society Conference | Tahoe 2022

Molecular Biophysics of Membranes

Poster Abstracts

57-POS Board 15 FLOW-SENSITIVE ACTIVATION OF MURINE OTOP CHANNELS BY NH4CL Ziyu Liang 1 ; Bochuan Teng 1 ; Emily Liman 1 ; 1 University of Southern California, Neurobiology, Los Angeles, CA, USA The otopetrin proteins (OTOPs) constitute a family of proton-selective ion channels found in diverse tissues, one of which (OTOP1) functions as a sour taste receptor. NH4Cl, which exists in equilibrium with the membrane permeable gas NH3, is used commonly as a means to alkalize the cytosol of cells. We therefore wondered whether currents through OTOP1 and other OTOP channels could be induced by exposure to NH4Cl. To test this possibility, murine OTOP channels were expressed HEK-293T cells and currents were measure by whole-cell patch-clamp recording. We found that large currents were induced in OTOP1 and OTOP2 but not OTOP3 expressing cells. Interestingly, the responses to NH4Cl, but not to HCl, showed a markedly flow- sensitivity. We considered two possible explanations for this phenomenon: first, the cell cytosol is similarly alkalinized by NH4Cl for all flow rates and OTOP1/2 are gated in a flow-sensitive manner. Second, the degree of alkalization of the cell cytosol is flow-sensitive and the gating of the channels is unaffected by varying flow rate. To distinguish between these possibilities, we combined whole-cell patch clamp recording with pH imaging using the pH indicator, pHlourin. We found that the degree of alkalization was sensitive to flow rate and correlated with the magnitude of the currents for both mOTOP1 and mOTOP2. Thus, flow-sensitivity is conferred by the rate of diffusion of NH4Cl across the membrane and not by mechanical gating of OTOP channels. The response of OTOP channels to NH4Cl is likely to have physiologically significance: for example, NH4Cl is a potent activator of the gustatory system and is used routinely as a control in gustatory nerve recordings. Future work will be needed to determine whether OTOP channels are required for this and other physiological responses to NH4Cl.

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