FIGURE 5.

Sphingosine influences ceramide channel formation in liposomes in a biphasic fashion. (A) The release of carboxyfluorescein from liposomes by C₁₆-ceramide (80 μg) alone or after the liposomes (90 μg of lipid) were pretreated with the indicated amounts of sphingosine (see Materials and Methods). The release is expressed as a fraction of the release achieved with 0.08% Triton X100. (B) The fluorescence level achieved in the experiments described in A 100 s after ceramide addition. Results are representative of two experiments.