PIP₂ Activates TRPV5 and Releases Its Inhibition by Intracellular Mg²⁺

The transient receptor potential type V5 channel (TRPV5) is a Ca²⁺-selective TRP channel important for epithelial Ca²⁺ transport. Intracellular Mg²⁺ causes a fast voltage-dependent block of the TRPV5 channel by binding to the selectivity filter. Here, we report that intracellular Mg²⁺ binding to the selectivity filter of TRPV5 also causes a slower reversible conformational change leading to channel closure. We further report that PIP₂ activates TRPV5. Activation of TRPV5 by PIP₂ is independent of Mg²⁺. Yet, PIP₂ decreases sensitivity of the channel to the Mg²⁺-induced slow inhibition. Mutation of aspartate-542, a critical Mg²⁺-binding site in the selectivity filter, abolishes Mg²⁺-induced slow inhibition. PIP₂ has no effects on Mg²⁺-induced voltage-dependent block. Thus, PIP₂ prevents the Mg²⁺-induced conformational change without affecting Mg²⁺ binding to the selectivity filter. Hydrolysis of PIP₂ via receptor activation of phospholipase C sensitizes TRPV5 to the Mg²⁺-induced slow inhibition. These results provide a novel mechanism for regulation of TRP channels by phospholipase C–activating hormones via alteration of the sensitivity to intracellular Mg²⁺.