Triphenylphosphine oxide is a potent and selective inhibitor of the transient receptor potential melastatin-5 ion channel

TRPM5 is critical for linoleic acid-induced CCK secretion from the enteroendocrine cell line, STC-1

Fatty acid-induced stimulation of enteroendocrine cells leads to release of the hormones such as cholecystokinin (CCK) that contribute to satiety. Recently, the fatty acid activated G protein-coupled receptor GPR120 has been shown to mediate long-chain unsaturated free fatty acid-induced CCK release from the enteroendocrine cell line, STC-1, yet the downstream signaling pathway remains unclear. Here we show that linoleic acid (LA) elicits membrane depolarization and an intracellular calcium rise in STC-1 cells and that these responses are significantly reduced when activity of G proteins or phospholipase C is blocked. LA leads to activation of monovalent cation-specific transient receptor potential channel type M5 (TRPM5) in STC-1 cells. LA-induced TRPM5 currents are significantly reduced when expression of TRPM5 or GPR120 is reduced using RNA interference. Furthermore, the LA-induced rise in intracellular calcium and CCK secretion is greatly diminished when expression of TRPM5 channels is reduced using RNA interference, consistent with a role of TRPM5 in LA-induced CCK secretion in STC-1 cells.

Transient receptor potential channel type M5 is essential for fat taste

Until recently, dietary fat was considered to be tasteless, and its primary sensory attribute was believed to be its texture (Rolls et al., 1999; Verhagen et al., 2003). However, a number of studies have demonstrated the ability of components in fats, specifically free fatty acids, to activate taste cells and elicit behavioral responses consistent with there being a taste of fat. Here we show for the first time that long-chain unsaturated free fatty acid, linoleic acid (LA), depolarizes mouse taste cells and elicits a robust intracellular calcium rise via the activation of transient receptor potential channel type M5 (TRPM5). The LA-induced responses depend on G-protein-phospholipase C pathway, indicative of the involvement of G-protein-coupled receptors (GPCRs) in the transduction of fatty acids. Mice lacking TRPM5 channels exhibit no preference for and show reduced sensitivity to LA. Together, these studies show that TRPM5 channels play an essential role in fatty acid transduction in mouse taste cells and suggest that fatty acids are capable of activating taste cells in a manner consistent with other GPCR-mediated tastes.

Transient receptor potential channel type M5 is essential for fat taste

Until recently, dietary fat was considered to be tasteless, and its primary sensory attribute was believed to be its texture (Rolls et al., 1999; Verhagen et al., 2003). However, a number of studies have demonstrated the ability of components in fats, specifically free fatty acids, to activate taste cells and elicit behavioral responses consistent with there being a taste of fat. Here we show for the first time that long-chain unsaturated free fatty acid, linoleic acid (LA), depolarizes mouse taste cells and elicits a robust intracellular calcium rise via the activation of transient receptor potential channel type M5 (TRPM5). The LA-induced responses depend on G-protein-phospholipase C pathway, indicative of the involvement of G-protein-coupled receptors (GPCRs) in the transduction of fatty acids. Mice lacking TRPM5 channels exhibit no preference for and show reduced sensitivity to LA. Together, these studies show that TRPM5 channels play an essential role in fatty acid transduction in mouse taste cells and suggest that fatty acids are capable of activating taste cells in a manner consistent with other GPCR-mediated tastes.