Accumulation of lipophilic substances in the plasma membrane may affect the membrane lipid order and consequently affect the function of these proteins. Changes in the activity of the Na+/K+ -ATPase, which is the major active transport system responsible for the electrochemical potential in mammalian cells, can therefore be an indication of the effect that a chemical may have on the viability of the cell membrane and possibly the whole cell. - [Read Hamster Ovary Cell NA+/K+ -ATPase Test]
Plasma membranes are isolated from the yeast Saccharomyces cerevisiae. The cell wall is initially digested by helicase, followed by hypoosmotic lysis and homogenization. Membranes are prepared by subsequent differential centrifugation. The activity of the H+-ATPase is then determined by measuring the amount of inorganic phosphate released from ATP. - [Read Yeast Plasma Membrane H+ -ATPASE Toxcity Test Protocol]