The whole cell patch clamp experiments and intracellular Ca2+ measurement demonstrated that depletion of polyP by the exopolyphosphatase scPPX1 inhibited TRPM8 currents and Ca2+-entry. To understand whether the effect of polyP
is direct or indirect on the TRPM8 channel protein, we examined the single channel properties of TRPM8 incorporated in planar lipid bilayers and the effect of subsequent treatment of the protein with scPPX1. The purified TRPM8 protein
derived in dodecylmaltoside (DDM) micelles was incorporated into lipid micelles consisting of a mixture of 1-palmitoyl-2-oleoyl-glycero-3-phosphoco line and 1-palmitoyl-2-oleoyl-glycero-3-phosphoet hanolaminein POPC/POPE (3:1,
v/v), and then into planar lipid bilayers of the same lipid composition between aqueous solutions of 150 mM KCl, 0.2 mM MgCl2 in 20 mM Hepes, pH 7.2. The presence of Mg2+ in the experimental solution was required to sustain normal
channel activity of TRPM8 with optimal concentration of 0.2 mM. Higher concentrationsof Mg2+ (≥2 mM) evoked an inhibition of TRPM8 currents. We also found that the presence of Mg2+ was necessary during the protein purification.