Pharmacological Potentiators of TRPM5 Channel Activity

Abstract

TRPM5 belongs to the ‘melastatin’ transient receptor potential subfamily, fluxes mainly Na+, and is activated by cytosolic Ca2+ increases (< 1 μM). TRPM5 activates and deactivates rapidly even during sustained Ca2+ rises, which leads to transient membrane depolarization kinetics. Only the Ca2+ ionophore ionomycin yielded significant and transient membrane potential (MP) signals in HEK293 cells stably expressing TRPM5. Various agonists for endogenous Gq‐GPCRs induced significant Ca2+ signals, but did not or only weakly activate TRPM5. Five tool potentiators were assessed using two TRPM5‐expressing cell clones, and various pharmacological concentrations of the indirect stimulator ionomycin. For both cell lines, potencies and efficacies of potentiators were best using an EC80 (rather than an EC20) concentration of ionomycin. This indirectly indicates that maximal cytosolic Ca2+ increases lead only to submaximal TRPM5 activation. EC60–80 concentrations of ionomycin yielded acceptable MP assay statistics, and a focused compound library was tested to find further and more potent TRPM5 potentiators. 114 TRPM5 potentiator hits were found (EC50 values: 0.11 –40 μM), and 67 thereof confirmed in a patch clamp assay. 38 of these novel TRPM5 potentiators increased currents over 100%. This work was supported by the Novartis Institutes for BioMedical Research (NIBR).