KINETICS OF PLASMA-MEMBRANE ELECTRON-TRANSPORT IN A PULMONARY ENDOTHELIAL CELL-COLUMN

Thiazine dyes such as toluidine blue O (TBO) are reduced at the lumina l endothelial surface. The purpose of this study was to determine the rate of this reaction in endothelial cells in culture. A multiple indi cator dilution method was used to measure the reaction kinetics during transient passage of a TBO-containing bolus through a chromatographic column filled with bovine pulmonary arterial endothelial cells grown on microcarrier beads (cell-column). A bolus containing TBO and an ine rt extracellular reference indicator (FITC-Dextran) was injected upstr eam of the cell-column, and the indicator concentrations were measured downstream using on-line photodetection. The effects of column flow r ate, PO2, and TBO concentration were studied. The fraction of TBO redu ced upon passage through the cell-column decreased with increasing flo w indicating that the reaction rate rather than TBO delivery controlle d TBO reduction. The fraction of TBO reduced did not change with PO2 o r dose in the ranges studied. TBO reduction was about 10 times that fo r steady state TBO sequestration by these cells which, along with the lack of a PO2 effect indicates that the rapid rate of reduction is not the rate-limiting step in steady state sequestration. [S0090-6964(98) 00901-1].