Fig. 5.

Sphingosine channels in erythrocyte plasma membranes have diameters less than 2 nm. In the main figure, erythrocytes (4 mg hemoglobin/mL) were added to solutions equiosmolar in test nonelectrolytes or isolation buffer and incubated for 15 min with sphingosine at the concentrations indicated. The percent lysis of the erythrocytes is the amount of hemoglobin released expressed as a percentage of the total hemoglobin released after addition of Triton X-100. The inset is a replot of the data from the main figure portraying erythrocyte lysis as a function of sphingosine concentration. The symbols in the inset are as follows: filled circles, NaCl; open circles, glucose; filled triangles, sucrose; open triangles, raffinose; filled squares, PEG-1500. The data are means ± SD of duplicates from three separate experiments (generally error bars are smaller than the symbols). It was previously reported that sphingosine causes hemolysis (52).