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Emerging Concepts in Ion Channel Biophysics
Poster Abstracts
62
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.