Interplay of Ca²⁺ and PIP₂ in TMEM16A channel function.

Area of Science:

• Ion channel physiology
• Membrane biophysics
• Cell signaling

Background:

• The TMEM16A channel is a Ca²⁺-activated chloride channel crucial for various physiological processes.
• Channel activity depends on both Ca²⁺ and the phospholipid PIP₂.
• PIP₂-dependent channels exhibit rundown in excised patches due to PIP₂ depletion.

Purpose of the Study:

• To investigate the influence of intracellular Ca²⁺ concentration on the rundown kinetics of TMEM16A currents.
• To elucidate the mechanisms by which Ca²⁺ modulates PIP₂ regulation and TMEM16A channel activity.

Main Methods:

• Inside-out patch-clamp recordings from Xenopus laevis oocytes.
• Manipulation of intracellular Ca²⁺ concentrations.
• Application of Mg-ATP, a phospholipase C (PLC) inhibitor, and diC8-PIP₂.

Main Results:

• TMEM16A current rundown is accelerated by elevated intracellular Ca²⁺, with half-maximal acceleration around 150 µM Ca²⁺.
• Ca²⁺-activated PLC and phosphatases contribute to PIP₂ degradation, enhancing rundown.
• Refuelling with Mg-ATP and PLC inhibition slowed rundown, indicating a balance between PIP₂ resynthesis and degradation.
• Directly supplying PIP₂ prevented rundown, confirming its critical role.

Conclusions:

• Ca²⁺ acts as a dual modulator of TMEM16A, directly gating the channel and indirectly promoting inhibition via PIP₂ hydrolysis and dephosphorylation.
• Enzymatic degradation pathways involving PLC and phosphatases are key mediators of Ca²⁺-induced PIP₂ depletion and TMEM16A rundown.
• Understanding these regulatory mechanisms is vital for comprehending TMEM16A channel function in physiological and pathological contexts.