Emerging Concepts in Ion Channel Biophysics

Emerging Concepts in Ion Channel Biophysics

Poster Abstracts

67-POS Board 67 Voltage-dependent Activation of TMEM16A, a Calcium-Activated Chloride Channel Guadalupe Segura-Covarrubias 1 , Silvia Cruz-Rangel 2 , José J. De Jesús-Pérez 2 , Ataúlfo Matinez Torres 3 , Patricia Pérez-Cornejo 2 , Jorge Arreola 2 . 1 Instituto Potosino de Investigación Científica y Tecnológica, San Luis Potosí, San Luis Potosí, Mexico, 2 Universidad Autónoma de San Luis Potosí, San Luis Potosí, San Luis Potosí, Mexico, 3 Instituto de Neurobiología UNAM, Querétaro, Querétaro, Mexico. The Ca 2+ -activated Cl- channel (CaCC) TMEM16A is widely expressed and play relevant role in critical physiological processes. The mechanism of activation of TMEM16A is complex. It involves an increase in intracellular Ca 2+ concentration ([Ca 2+ ] i ) along with membrane depolarization. In addition, highly permeant anions and protons facilitate channel gating. It has been proposed that the voltage dependence of TMEM16A result from the voltage-dependent binding of Ca 2+ . In this work, we show that WT TMEM16A and TMEM16A lacking the high affinity Ca 2+ binding site are activated by voltage in the absence of intracellular Ca 2+ albeit to a lower extent than Ca 2+ . Even so, tannic acid, specific blocker TMEM16A, inhibited the currents recorded from cells dialyzed with zero and with 0.2 μM Ca 2+ with the same apparent affinity indicating that tinny currents are flowing through TMEM16A. The current magnitude increased after eliminating 448 EAVK 451 located in the first intracellular loop of TMEM16A with high affinity Ca 2+ binding site (E702Q/E705Q) mutated. The magnitude of the currents through this channel depended on the [Cl - ] e and has an anion selectivity similar to that of the wild channel. Deleting 5 glutamic acids located before 448 EAVK 451 did not significant change the voltage dependence. Based on these results we propose that TMEM16A has an intrinsic voltage dependence that is negatively regulated by the first intracellular loop. Thus, the voltage dependence TMEM16A comes from the intrinsic voltage dependence here described and from the voltage dependence of the Ca 2+ binding.

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