Impermeability of rabbit erythrocytes to prostaglandins

Washed rabbit erythrocytes were suspended in Tris-electrolyte buffer containing [3H]prostaglandin (PG) E1, F1alpha, F2alpha, or A1 and one 14C-labeled compound such as sucrose. After up to 24 h of incubation, aliquots of centrifuged, packed cells and supernatant were oxidized and the 3H and 14C samples were counted. The mean sucrose space of the packed cell was 7.4%. After 1 min the E1, F1alpha, and F2alpha spaces were 16, 15.4, and 10.0%, respectively, and showed no increase even after 24 h of incubation at either 23 or 5 degrees C. At 23 degrees C the initial (0.5 min) PGA1 and thiourea spaces were 94 and 75%, respectively, whence the PGA1, but not the thiourea, space declined, reaching 30% at 4 h. The large initial uptake of PGA1 was eliminated at 5 degrees C, while it was accentuated at pH 6.8 or at a PGA1, concentration of 10(-3) M. 14C-Labeled arachidonic, octanoic, and other non-PG fatty acids gave apparent distribution spaces of 140-300%. These results show that PG's can partition into rabbit erythrocyte membranes, but the intracellular volume of the erythrocytes is not freely accessible to these autacoids. The implications of the finding that some cell membranes are impermeable to prostaglandins are discussed.