Diclofenac, a nonsteroidal anti‐inflammatory drug, is an antagonist of human TRPM3 isoforms

The effects of diclofenac (Dic), an acetic acid derivative‐type nonsteroidal anti‐inflammatory drug, were examined on the function of transient receptor potential (TRP) melastatin (TRPM) 3 (TRPM3) in human embryonic kidney 293 cell‐line (HEK293) cells with recombinant human TRPM3 isoforms (TRPM3(1325), TRPM3‐3, TRPM3‐9, and TRPM3‐S) and in a neuroblastoma cell line human neuroblastoma IMR‐32 cells (IMR‐32 cells) derived from human peripheral neurons. TRPM3 responses evoked by pregnenolone sulfate (PregS) were effectively inhibited by Dic in a concentration‐dependent manner in Ca(2+) measurement and electrophysiological assays. The apparent IC (50) for PregS‐induced Ca(2+) response of TRPM3(1325), TRPM3‐3, and TRPM3‐9 was calculated to be 18.8, 42.5, and 7.1 μmol/L, respectively. The TRPM3‐dependent Ca(2+) responses evoked by nifedipine, another TRPM3 agonist, were also significantly inhibited by Dic. In contrast, aceclofenac, an acetoxymethyl analog of Dic, had no effects on PregS‐induced TRPM3 responses. Constitutive channel activity of TRPM3‐S without TRPM3 agonists was substantially inhibited by Dic, ruling out the possibility of interaction of Dic against TRPM3 agonists to the channel binding sites. Moreover, Dic reversibly inhibited TRPM3 single‐channel activity recorded in excised outside‐out patches without affecting the channel conductance. In differentiated neuronal IMR‐32 cells with endogenous TRPM3, Dic inhibited PregS‐evoked Ca(2+) responses with an apparent IC (50) of 17.1 μmol/L. Taken together, our findings demonstrate that Dic inhibits human TRPM3 without interacting with the channel pore.