Effect of cell substratum on lateral mobility of lipids in the plasma membrane of vascular endothelial cells

Bovine vascular endothelial cells can be maintained in a highly differentiated state in vitro, either by the addition of fibroblast growth factor (FGF) to the culture medium or by plating the cells on extracellular matrix (ECM)-coated dishes. Under these conditions the cells proliferate actively and at confluence form a tightly packed monolayer composed of nonoverlapping polarized cells. A fluorescence recovery after photobleaching method was used to determine the lateral mobility coefficient D of the lipophilic fluorescent probe, 5N-(hexadecanoyl)-aminofluorescein (HEDAF), in the basal and apical plasma membranes of endothelial cells under various culture conditions (cells on glass coverslips in the presence or absence of FGF, or cells plated on ECM in the exponential growth phase or at confluence). A heterogeneous distribution of lateral diffusion coefficients D was found in a given cell population. Nevertheless, for the basal membrane, a "mean" D value close to 2.0 x 10(-9) cm2/s was found for all the culture conditions. The "mean" D value of HEDAF in the apical pole was slightly higher when sparse cells were exposed to FGF (D = 2.2 x 10(-9) cm2/s) and was further enhanced when cells were growing or confluent on ECM-coated coverslips (D = 2.7 x 10(-9) cm2/s). On the other hand, when the cells were maintained in the absence of FGF on glass coverslips, similar "mean" D values were found in both cell poles (D = 2.0 x 10(-9) cm2/s). These results show that lateral mobility of lipids in endothelial plasmalemma varies in response to external factors such as FGF and the ECM.