Biophysicists found that greater electrical conductance was conferred by cell membrane's proteins when measuring the electric current passing through cell membranes, which are now called ion channels. Then a rich variety of channels has been isolated and analyzed from a wide range of cell membranes. Ion channels, proteins expressed by virtually all living cells that creates a pathway for charged ions from dissolved salts, including sodium, potassium, calcium, and chloride ions, to pass through the impermeant lipid cell membrane, are pore-forming membrane proteins that allow ions to pass through the channel pore.