Measurements of CO2, lactic acid and sodium bicarbonate secreted by cultured cells using a flow-through type pH/CO2 sensor system based on ISFET

We developed a pH/CO2 sensor system using two ion-sensitive field effect transistors (ISFETs) to evaluate the metabolic activity of cultured cells. One ISFET measures total pH changes and the other ISFET, covered with a gas-permeable silicon tube, measures pH changes due to CO2. These ISFETs were placed in a flow-through chamber with a window to be attached to a glass plate on which cells were cultured. Measurements were performed with a baseline solution of low buffer capacity. In the quantitative estimation of cellular products, we assumed that cells secreted CO2, lactic acid and sodium bicarbonate (NaHCO3), and then lactic acid and NaHCO3 proceeded to the neutralization reaction to form sodium lactate and additional CO2. We applied this system to evaluate the metabolic activity of bovine aortic endothelial cells (BAEC) and rabbit aortic smooth muscle cells (RASMC). The production of CO2 by RASMC was significantly higher than that by BAEC (204 ± 16 and 4.1 ± 0.3 × 108 molecules/cell/s, respectively). More NaHCO3 than lactic acid was produced in RASMC, whereas they were not significantly different in BAEC.