Single plasma membrane K+ channel detection by using dual-color quantum dot labeling

K+ channels are widely expressed in eukaryotic and prokaryotic cells, where one of their key functions is to set the membrane potential. Many K+ channels are tetramers that share common architectural properties. The crystal structure of bacterial and mammalian K+ channels has been resolved and provides the basis for modeling their three-dimensional structure in different functional states. This wealth of information on K+ channel structure contrasts with the difficulties to visualize single K+ channel proteins in their physiological environment. We describe a method to identify single Ca2+-activated K+ channel molecules in the plasma membrane of migrating cells. Our method is based on dual-color labeling with quantum dots. We show that >90% of the observed quantum dots correspond to single K+ channel proteins. We anticipate that our method can be adopted to label any other ion channel in the plasma membrane on the single molecule level.