By homogenising cells and centrifuging the homogenate, one can harvest the lighter density intracellular fractions to determine if cell signalling can be detected in intracellular compartments. These intracellular fractions are separated further on a sucrose density gradient and markers such as Na+/K+ ATPase is used to identify fractions containing plasma membrane material, while calnexin is used to identify fractions containing material from the ER.
