Forms nonselective divalent cation-conducting channels which mediate the influx of Na(2+), Ca(2+), Mg(2+), Mn(2+), Ba(2+), and Ni(2+) into the cytoplasm, leading to membrane depolarization. Impermeable to zinc ions. In addition, forms heteromultimeric ion channels with TRPM3 which are permeable for calcium and zinc ions. Essential for the depolarizing photoresponse of retinal ON bipolar cells. It is part of the GRM6 signaling cascade. May play a role in metastasis suppression. May act as a spontaneously active, calcium-permeable plasma membrane channel.