Gadolinium activates and sensitizes the vanilloid receptor TRPV1 through the external protonation sites

Gadolinium is a recognized blocker of many types of cation channels, including several channels of the transient receptor potential (TRP) superfamily. In this study, we demonstrate that Gd3+, in addition to its blocking effects, activates and potentiates the recombinant vanilloid receptor TRPV1 expressed in HEK293T cells. Whole-cell currents through TRPV1 were induced by Gd3+ with a half-maximal activation achieved at 72 μM at +40 mV. Gd3+, at concentrations up to 100 μM, lowered the threshold for heat activation and potentiated the currents induced by capsaicin (1 μM) and low extracellular pH (6). Higher concentrations of Gd3+ (>300 μM) blocked the TRPV1 channel. Neutralizations of the two acidic residues, Glu600 and Glu648, which are the key residues conferring the proton-sensitivity to TRPV1, resulted in a loss of Gd3+-induced activation and/or a reduction in its potentiating effects. A trivalent nonlanthanide, Al3+, that possesses much a smaller atomic mass than Gd3+ blocked but did not activate or sensitize the TRPV1 channel. These findings indicate that Gd3+ activates and potentiates the TRPV1 by neutralizing two specific proton-sensitive sites on the extracellular side of the pore-forming loop.