Identification and classification of a new TRPM3 variant (γ subtype)

TRPM3 is a non-selective cation channel that is activated by neural steroids such as pregnenolone sulfate, nifedipine, and clotrimazole. Despite the number of TRPM3 variants, few reports have described functional analyses of these different TRPM3 types. Here we identified a new TRPM variant from mouse dorsal root ganglion, termed TRPM3 gamma 3. We classified TRPM3 gamma 3 and another known variant (variant 6) into the y subtype, and analyzed the TRPM3 gamma variants. mRNA expression of TRPM3 gamma was higher than that of TRPM3 alpha variants in the mouse dorsal root ganglion. In Ca2+-imaging of HEK293 cells expressing either the TRPM3 gamma variants or TRPM3 alpha 2, increases in cytosolic Ca2+ concentrations ([Ca2+],) induced by pregnenolone sulfate or nifedipine were smaller in cells expressing the TRPM3 gamma variants compared to those expressing TRPM3 alpha 2. On the other hand, co-expression of TRPM3 gamma variants had no effect on [Ca2+], increases induced by pregnenolone sulfate or nifedipine treatment of HEK293 cells expressing TRPM3 alpha 2. In Xenopus oocytes, small responses of TRPM3 gamma variants to chemical agonists compared to TRPM3 alpha 2 were also observed. Interestingly, Xenopus oocytes expressing TRPM3 alpha 2 displayed heat-evoked currents with clear thresholds of about 40 degrees C that were larger than those evoked in oocytes expressing TRPM3 gamma variants. Overall, these findings indicate that TRPM3 gamma variants have low channel activity compared to TRPM3 alpha.