On the Mechanism of TBA Block of the TRPV1 Channel

Abstract

The transient receptor potential vanilloid 1 (TRPV1) channel is a nonselective cation channel activated by capsaicin and responsible for thermosensation. To date, little is known about the gating characteristics of these channels. Here we used tetrabutylammonium (TBA) to determine whether this molecule behaves as an ion conduction blocker in TRPV1 channels and to gain insight into the nature of the activation gate of this protein. TBA belongs to a family of classic potassium channel blockers that have been widely used as tools for determining the localization of the activation gate and the properties of the pore of several ion channels. We found TBA to be a voltage-dependent pore blocker and that the properties of block are consistent with an open-state blocker, with the TBA molecule binding to multiple open states, each with different blocker affinities. Kinetics of channel closure and burst-length analysis in the presence of blocker are consistent with a state-dependent blocking mechanism, with TBA interfering with closing of an activation gate. This activation gate may be located cytoplasmically with respect to the binding site of TBA ions, similar to what has been observed in potassium channels. We propose an allosteric model for TRPV1 activation and block by TBA, which explains our experimental data.

Extracellular Quaternary Ammonium Blockade of Transient Receptor Potential Vanilloid Subtype 1 Channels Expressed in Xenopus laevis Oocytes

“…In Xenopus laevis oocytes, we have found that lidocaine and QX-314 exert biphasic effects on TRPV1 channels, inhibiting capsaicin-evoked TRPV1 currents at lower (micromolar) concentrations and activating TRPV1 channels at higher (millimolar) concentrations. Whereas the mechanisms are unknown, studies into the permeation and gating pathway of TRPV1 have found, similar to results obtained with Kv channels, that permanently charged quaternary ammonium compounds are able to potently block TRPV1 intracellularly, thus delimiting similarities among these seemingly disparate family members (Oseguera et al, 2007;Jara-Oseguera et al, 2008). However, it remains unclear whether TRPV1 is also susceptible to extracellular inhibition by quaternary ammonium compounds.…”

“…To more directly assess the role of charge in TRPV1 inhibition, we characterized extracellular block by the quaternary permanently charged amines, TEA and TMA, which have been instrumental in the structure-function study of potassium channel pore regions. More recently, these compounds have been successfully used to help define the structure and basic biophysical properties of the intracellular TRPV1 channel pore (Oseguera et al, 2007;Jara-Oseguera et al, 2008). In our current study, similar to results with both lidocaine and QX-314, extracellular application of TEA produced a reduction in capsaicin-evoked inward currents, albeit with substantially higher affinity (Fig.…”

Identification of a Binding Motif in the S5 Helix That Confers Cholesterol Sensitivity to the TRPV1 Ion Channel

“…To further explore the underlying cause of these observed cholesterol decreases in capsaicin-induced rTRPV1 currents, we performed noise analysis on rTRPV1 channels (37) in the presence and absence of cholesterol. Fig.…”

Biological physics in México

“…Biological physics research at Universidad de Sonora [25][26][27][28][29] has been growing well in recent years. Although institutions like the Instituto de Fisiología Celular [30][31][32] at UNAM and the Center for Research and Advanced Studies (Cinvestav) offer graduate programs in biophysics, their emphasis is more in the biological side of the subject [32,33]. With regards to BP, Cinvestav's physics department is already developing a research core [34][35][36][37][38][39], which other departments at Cinvestav are also doing research in biological physics and related issues [40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57].…”