Fig. 1. Monodansycadaverine (MDC)-labeled vesicles are induced by starvation. (A) CHO cells were incubated in -MEM medium (control cells) or in EBSS medium (starved cells) at 37°C for two hours. Following this incubation period, both starved and control cells were incubated with MDC at 0.05 mM for 10 minutes at 37°C and then washed four times with PBS pH 7.4. Cells were immediately analyzed by fluorescence microscopy using an inverted microscope as described in Materials and Methods. Images were obtained with a CCD camera and processed using the Meta View program. (B) Cells were incubated in -MEM medium (control cells) or in EBSS medium (starved cells) at 37°C for two hours. Following this incubation period, both starved and control cells were incubated with MDC 0.05 mM for 10 minutes at 37°C, washed four times with PBS pH 7.4, and then lysed in 10 mM Tris-HCl, pH 8 containing 0.1% Triton X-100. Intracellular MDC was measured by fluorescence photometry as indicated in Experimental Procedures. The data represent the mean±s.e.m. of at least three independent experiments. (C) CHO cells were incubated in starvation medium for different periods of time. MDC labeling and measurement was performed as in B. Data are representative of at least three independent experiments.