Pharmacological characterization of TMEM16A currents

Area of Science:

• Ion channel physiology
• Molecular pharmacology

Background:

• Transmembrane protein 16A (TMEM16A) is identified as a subunit of calcium-activated chloride channels (CACCs).
• Previous studies utilized pharmacological agents to explore CACC functions, but their specific impact on TMEM16A currents remains under-characterized.

Purpose of the Study:

• To systematically investigate the voltage and concentration-dependent effects of established and novel CACC inhibitors on TMEM16A currents.
• To evaluate the potency and characteristics of niflumic acid, anthracene-9-carboxylic acid, CACC(inh)A01, and T16A(inh)A01 as TMEM16A inhibitors.

Main Methods:

• Utilized the whole-cell patch clamp technique to record TMEM16A currents.
• Expressed human TMEM16A in HEK293 cells for stable current recording.
• Characterized the inhibitory effects (IC50, voltage-dependence, deactivation kinetics) of four different CACC inhibitors.

Main Results:

• All four inhibitors (niflumic acid, A-9-C, CACC(inh)A01, T16A(inh)A01) inhibited TMEM16A currents, with IC50 values ranging from 1.5 to 58 μM.
• Niflumic acid and A-9-C showed reduced efficacy at negative potentials and altered deactivation kinetics, consistent with previous CACC studies.
• CACC(inh)A01 and T16A(inh)A01 demonstrated potent, voltage-independent inhibition without affecting deactivation rates.

Conclusions:

• Findings support the hypothesis that TMEM16A encodes CACCs, particularly in vascular smooth muscle, based on the effects of niflumic acid and A-9-C.
• CACC(inh)A01 and T16A(inh)A01 are identified as highly potent TMEM16A inhibitors with voltage-independent action.
• These novel inhibitors represent valuable pharmacological tools for future investigations into the functional roles of TMEM16A channels.