Biphasic currents evoked by chemical or thermal activation of the heat-gated ion channel, TRPV3

2-Aminoethyl diphenylborinate was recently identified as a chemical activator of TRPV1, TRPV2, and TRPV3, three heat-gated members of the transient receptor potential vanilloid (TRPV) ion channel subfamily. Here we demonstrated that two structurally related compounds, diphenylboronic anhydride ( DPBA) and diphenyltetrahydrofuran (DPTHF), can also modulate the activity of these channels. DPBA acted as a TRPV3 agonist, whereas DPTHF exhibited prominent antagonistic activity. However, all three diphenyl-containing compounds promoted some degree of channel activation or potentiation, followed by channel block. Strong TRPV3 activation by DPBA often leads to the appearance of a secondary, enhanced, current phase. A similar biphasic response was observed during TRPV3 heat stimulation; an initial, gradually sensitizing phase (I-1) was followed by an abrupt transition to a secondary phase (I-2). I-2 was characterized by larger current amplitude, loss of outward rectification, and alterations in the following properties: permeability among cations; ruthenium red and DPTHF sensitivity; temperature dependence; and voltage-dependent gating. The I-1 to I-2 transition depended strongly on TRPV3 current density. Removal of extracellular divalent cations resulted in heat-evoked currents resembling I-2, whereas mutation of a putative Ca2+-binding residue in the pore loop domain, aspartate 641, facilitated detection of the I-1 to I-2 transition, suggesting that the conversion to I-2 resulted from the agonist- and time-dependent loss of divalent cationic inhibition. Primary keratinocytes overexpressing exogenous TRPV3 also exhibited biphasic agonist- evoked currents. Thus, strong activation by either chemical or thermal stimuli led to biphasic TRPV3 signaling behavior that may be associated with changes in the channel pore.