The impermeability of the basic cell membrane to thromboxane-B2' prostacyclin and 6-keto-PGF 1 alpha

Washed rabbit red blood cells (RBCs) were suspended in electrolyte solution containing 3H-labeled prostacyclin (PGI2), thromboxane (TxB2) or 6-keto-PGF 1 alpha and 14C-labeled sucrose or thiourea. following 1 to 30 min incubation with 14C-sucrose, 3H-TxB2 or 3H-6-keto-PGF 1 alpha, the 14C or 3H space of packed RBCs remained essentially constant, yielding mean values (+/- S.E.) for all time periods of 6.1 +/- 0.3, 9.5 +/- 0.5 and 6.5 +/- 0.4%, respectively. After 1 min of incubation at 4 degrees or 23 degrees C at a pH of 7.4 or 8.5 with trace amounts (10(-9)M) of 3H-PGI2 or in the presence of added PGI2 (10(-5)M) or ethacrynic acid (1.6 x 10(-4)M), the apparent PGI2 space of packed RBCs ranged from 16 to 27%, decreasing to about 7% by 30 min. When RBCs were resuspended in fresh 3H-PGI2 every 5 min, their 3H content increased very slowly (apparent PGI2 space less than 40% at 30 min) as compared to thiourea (distribution space greater than 80% within 5 min). Over 90% of this 3H activity was lost from the RBCs in less than 2 min during elution at 4 degrees or 23 degrees C. It is concluded that RBC membranes and thus, presumably, the basic cell membrane in general, is not fundamentally permeable to PGI2, 6-keto-PGF 1 alpha or TxB2. Hence, the effective entry of these cyclooxygenase products into some cells or their passage across tight-junctional capillaries or epithelial membranes must require facilitated or active transport processes as was shown to be the case for E, F and A PGs. This implies that the distribution, pharmacological action and metabolism of these and presumably all related cyclooxygenase products are selective rather than unrestricted.