TRPV1 is a cation channel that was originally cloned as the capsaicin (or """"""""hot pepper"""""""") receptor. TRPV1 is expressed in the peripheral nervous system where it serves to sense and integrate a large number of noxious stimuli such as heat, protons, and lipid mediators. Very recent data indicate that TRPV1 is also expressed in some epithelial cells (e.g., those of the colon, lung, and bladder) and plays a vital role in sensing noxious stressors including wall tension and cellular acidosis. Based upon Northern analysis and RNase protection assays, others have postulated the existence of novel splice variants of TRPV1 expressed only in the kidney. To date, convincing splice variants have not been described in any tissue. In the course of identifying a rat kidney TRPV1 clone, we discovered several novel splice variants of TRPV1 predicted to encode proteins with either small or large C-terminal deletions. These variants were not found in central or peripheral nervous system. In other models, including the related TRPC4 channel, splice variants have encoded dominant negative-acting channel subunits. In addition, we noted anti-TRPV1 immunoreactivity in lysates prepared from renal epithelial MDCK cells; furthermore, this immunoreactivity could be downregulated by protracted treatment with the TRPV1 agonist, capsaicin. Moreover, MDCK cells exhibited robust calcium transients in response to TRPV1 agonists. In aggregate, these data suggested an intact TRPV1 system in kidney tubule cells with unique regulatory features (i.e., splice variants). As such, the first objective is to identify the anatomic and subcellular localization of TRPV1 and of the novel kidney-specific TRPV1 splice variants in the mammalian kidney, through a combination of immunoblotting, immunohistochemistry, RNase protection, and in situ hybridization techniques. The second objective is to describe the functional significance of variant TRPV1 expression in the kidney, via fura-2-based calcium imaging, protein interaction strategies, and electrophysiological methods. The long-term objectives are to establish the sensory role of TRPV1 in the kidney (through a combination of anatomic and functional studies), and to determine whether one of these unique kidney-specific splice products encodes either a channel with unique properties, or an inhibitor or modulator of TRPV1 function. In addition, such a reagent might have potential therapeutic utility with respect to this important pathway mediating nociception.
