Contrasting effects of phosphatidylinositol 4,5-bisphosphate on cloned TMEM16A and TMEM16B channels.

BACKGROUND AND PURPOSE

Ca -activated Cl channels (CaCCs) are gated open by a rise in intracellular Ca concentration ([Ca ] ), typically provoked by activation of G -protein coupled receptors (G PCR). G PCR activation initiates depletion of plasmalemmal phosphatidylinositol 4,5-bisphosphate (PIP ). Here, we determined whether PIP acts as a signalling lipid for CaCCs coded by the TMEM16A and TMEM16B genes.

EXPERIMENTAL APPROACH

Patch-clamp electrophysiology, in conjunction with genetically encoded systems to control cellular PIP content, was used to define the mechanism of action of PIP on TMEM16A and TMEM16B channels.

KEY RESULTS

A water-soluble PIP analogue (diC8-PIP ) activated TMEM16A channels by up to fivefold and inhibited TMEM16B by ~0.2-fold. The effects of diC8-PIP on TMEM16A currents were especially pronounced at low [Ca ] . In contrast, diC8-PIP modulation of TMEM16B channels did not vary over a broad [Ca ] range but was only detectable at highly depolarized membrane potentials. Modulation of TMEM16A and TMEM16B currents was due to changes in channel gating, while single channel conductance was unaltered. Co-expression of TMEM16A or TMEM16B with a Danio rerio voltage-sensitive phosphatase (DrVSP), which degrades PIP , led to reduction and enhancement of TMEM16A and TMEM16B currents respectively. These effects were abolished by an inactivating mutation in DrVSP and antagonized by simultaneous co-expression of a phosphatidylinositol-4-phosphate 5-kinase that catalyses PIP formation.

CONCLUSIONS AND IMPLICATIONS

PIP acts as a modifier of TMEM16A and TMEM16B channel gating. Drugs interacting with PIP signalling may affect TMEM16A and TMEM16B channel gating and have potential uses in basic science and implications for therapy.