nprofile1qy2hwumn8ghj7un9d3shjtnddaehgu3wwp6kyqpqxfh4n3lx98vn7470hdfc6fe2umtkyjv0y2k586act7n3v84nme0stmv3l9 (nprofile…v3l9) Some info here: https://en.wikipedia.org/wiki/Taste#Saltiness
There's an ion channel that lets sodium ions through, and that activates the receptor. Other elements in the same column of the periodic table can trigger it too, such as potassium.