HEK 293 cells endogenously express low levels of TRPML1 and TRPML3. Their expression can be increased in HEK 293 cells by transfecting the cells with plasmids encoding these proteins.
Also, chemical agents like ML-SA1 (TRPML1 agonist) and MK6-83 (TRPML3 agonist) can also be used to activate these endogenous channels in HEK 293 cells without transfection.