In 1990 Lisa Matsuda cloned CB1, the first cannabinoid receptor discovered in rats, and Shawn Munro cloned a second receptor (CB2 in humans) in 1993. (scientificamerican.com)
This suggests that unlike all the other tastes we've cracked so far, salt perception has two parts: some receptor that's involved in making salt attractive, and a second receptor, or other biological process, that makes it unattractive at high concentrations. (discovermagazine.com)
Lassa virus entry in susceptible species involves a pH - dependent switch to a second receptor within the lysosome. (science.sciencemag.org)