Endothelin-1 (ET-1), a member of a 21-amino acid peptide family of endothelins, can be derived from various cells of the cerebromicrovascular compartment (endothelium, smooth muscle), astrocytes, and some neurons. ET-1 is a potent and prolonged vasoconstrictor. Increased levels of ET-1 in plasma or cerebrospinal fluid of patients with hypertension, stroke, head trauma, and subarachnoid hemorrhage (SAH) have implicated ET-1 as a mediator of cerebrovascular responses in these disorders. Recently, we described that cultured human brain endothelial cells (HBEC) secrete ET-1 in response to various vasoactive stimuli (angiotensin II, arginine-vasopressin) and express receptors for ET-1. In this study, we examined the effects of the vasoactive peptide endothelins (ET-1, ET-2, ET-3, S6b, S6c) on the release of 51Cr, production of inositol triphosphate (IP3), and release of arachidonic acid (AA) in HBEC. ET-1 induced a dose-dependent release of 51 Cr (EC50 = 7+/-2 nM), transient increase of IP3 (EC50 = 0.67 +/- 0.09 nM), and sustained release of AA (EC50= 59+/-7 nM) from HBEC. Under the same experimental conditions, viability of the cells was preserved (>97%) as assessed by exclusion of the vital dye trypan blue, and release of lactate dehydrogenase. The ET-1-induced 51Cr release, formation of IP3, and AA release from HBEC were competitively inhibited by the selective ETA subtype receptor antagonist BQ123. ET-1-stimulated 51Cr and AA release from HBEC were potentiated by protein kinase C (PKC) activator phorbol-myristate ester, and abolished by H7, an inhibitor of PKC. Dexamethasone, indomethacin, acetylsalicylic acid, imidazole, as well as the inhibitor of protein kinase A, H8, had no effect on 51Cr release. The results suggest that ETA receptor-mediated activation of PKC and increase in the HBEC """"""""permeability"""""""" for low molecular weight molecules in response to excessive release of endothelins from either HBEC or surrounding tissues during pathologic conditions may contribute to alterations of blood-brain barrier permeability.
