Blood-brain barrier Na transporters in ischemic stroke.
- Martha E O'Donnell
- Advances in pharmacology
The effect of endothelins (ETs) on sodium/hydrogen (Na+/H+) antiport system was examined in cultured rat brain capillary endothelium (RBEC). ET-1, ET-2, and ET-3 stimulated Na+ uptake into RBEC with similar half-maximal stimulation (EC50) values (0.7, 0.6, and 1.1 nM, respectively). This reaction was inhibited by the Na+/H+ antiport inhibitor, N-(ethyl-N-isopropyl)-amiloride (EIPA). The selective endothelin A (ETA) receptor-antagonist (cyclo-D-Trp-D-Asp-Pro-D-Val-Leu (BQ123)), but not endothelin B (ETB) receptor-antagonists ((Cys11, Cys15)-ET-1 (IRL1038) or N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma MeLeu-D-Trp(COOMe)-D-Nle-ONa (BQ788)), inhibited both ET-1- and ET-3-stimulated Na+ uptake, indicating ETA-receptor mediation. The protein kinase C (PKC) activator (phorbol 12-myristate 13-acetate (PMA)) failed to stimulate Na+ uptake. The calcium-calmodulin (CaM) inhibitor (W7) reduced ET-1-stimulated Na+ uptake by 50%, whereas the PKC inhibitor (staurosporine) had no effect, indicating that ET-1 stimulation of the Na+/H+ antiport system is linked to a CaM-dependent and PKC-independent pathway.