The Cytosensor Microphysiometer assay is an in vitro cellular toxicity test used to evaluate ocular irritancy. A microphysiometer is used to detect and monitor the extracellular changes in pH in L929 (mouse fibroblast) cells after exposure to a test material. Changes in the pH are caused by variations in the metabolic rate, measured indirectly as a function of changes in extracellular acidification.
Metabolism in living cells is tightly coupled to cellular ATP usage and extracellular release of acidic byproducts such as protons, lactic acid, and CO2. Events that disturb the metabolism of cells (such as toxic assault by a test material) will result in a change in the rate at which the cell releases these metabolic byproducts. The amount of these acidic byproducts can be measured by changes in the pH of the culture medium surrounding the cells.
In a microphysiometer, measuring of changes in pH occurs in the sensor chamber. A silicon chip that serves as a light addressable potentiometric sensor (LAPS) makes up the lower surface of the chamber. A small light producing diode (LED) is located in the Cytosensor under the chamber. This LED pulses light on the LAPS chip producing a photocurrent that is detected by the exterior circuit formed by the framework. The Cytosensor monitors the changes in photocurrent as changes in the cells acidification rate. For specific assay procedures, please see Step-by-Step.