OTOP1 and kidney disorder: Multiple sour taste receptor candidates have been proposed such as acid-sensing ion channels (ASICs; Ugawa et al., 2003), hyperpolarization-activated cyclic nucleotide-gated potassium channels (HCNs; Stevens et al., 2001), potassium channels (Lin et al., 2004; Richter et al., 2004), polycystic kidney disease 2L1 (PKD2L1) and PKD1L3 heteromers (Huang et al., 2006; Ishimaru et al., 2006; Lopezjimenez et al., 2006), and Otop1 (Tu et al., 2018).