J Physiol 2025 Nov 30; doi: 10.1113/JP289257.

Interplay of Ca2+ and PIP2 in TMEM16A channel function.

???displayArticle.abstract???
The transmembrane member 16A (TMEM16A) forms a Ca2+-activated Cl- channel with widespread expression and diverse physiological roles. Activating these channels requires both Ca2+ and the acidic phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2). Like other PIP2-dependent channels, TMEM16A-mediated currents in excised patches display a characteristic time-dependent decline, known as rundown. We have reported that TMEM16A currents exhibit rapid rundown at high intracellular Ca2+ concentrations, providing a tractable system to study PIP2 regulation. Here, we investigated how intracellular Ca2+ affects rundown kinetics of TMEM16A currents by performing inside-out patch-clamp recordings from Xenopus laevis oocytes, where these channels are naturally abundant. We found that the rate of rundown is modulated by intracellular Ca2+ concentration, with elevated Ca2+ accelerating rundown in part by activating membrane-associated phospholipase C (PLC) and phosphatases. Refuelling kinases with Mg-ATP slowed rundown, and combining ATP with a PLC inhibitor further amplified this effect, highlighting the interplay between PIP2 resynthesis and enzymatic degradation. This study delineates the complex role of Ca2+ in TMEM16A regulation, proposing it as a dual modulator that gates the channel directly and promotes indirect inhibition through PIP2 dephosphorylation and hydrolysis by patch-associated enzymes. KEY POINTS: TMEM16A currents undergo Ca2+-accelerated rundown in excised inside-out patches due to PIP2 depletion. Rundown rate increases with intracellular Ca2+ concentration, with half-maximal acceleration at ∼150 µM Ca2+. Inhibiting phosphatases or refuelling kinases with Mg-ATP slows rundown but does not fully prevent it. Ca2+-activated phospholipase C (PLC) activity contributes to PIP2 degradation; PLC inhibition attenuates rundown. Co-application of diC8-PIP2 and Ca2+ prevents rundown, highlighting the dual role of Ca2+ in channel gating and PIP2 depletion.

???displayArticle.pubmedLink??? 41321027
???displayArticle.link??? J Physiol
???displayArticle.grants??? [+]