The Endoplasmic Reticulum-Located TRPV1 Channel Is Not Thermal Sensitive.

Abstract

Transient receptor potential vanilloid subfamily member 1 (TRPV1), also known as the capsaicin receptor, plays a central role in detecting noxious heat, regulating thermal homeostasis, and mediating inflammatory responses. TRPV1 is a cell membrane-associated, nonselective cation channel. TRPV1 activation triggers transmembrane depolarizing currents and elevates the level of cytosolic calcium. A large fraction of TRPV1 is known to reside in the endoplasmic reticulum (ER), and ligand-dependent activation of this fraction elicits calcium release from the ER. However, whether ER-located TRPV1 participates in the heat-evoked cytosolic calcium elevation remains unresolved. In this study, we heterologously expressed human TRPV1 in HEK293TN cells, which do not normally exhibit physiological responses to temperature variations, and recorded calcium changes in response to heat stimulation and capsaicin treatment in the presence of extracellular calcium and after its removal. Our experiments revealed that heat-evoked calcium responses were abolished in hTRPV1-expressing HEK293TN cells upon removal of extracellular calcium, whereas the TRPV1 agonist capsaicin still elicited an elevation of intracellular calcium. The restoration of extracellular calcium after its withdrawal recovered heat-evoked calcium responses. Our findings argue for differential sensitivity of TRPV1 pools (ER vs plasma membrane) for discriminating various physiological and noxious signals and may allow for elucidating the structural basis of temperature-dependent gating.