Endothelin-1-induced contraction in cerebral vessels mediated by phospholipase C/protein kinase C cascade

Endothelin (ET) vasoconstricts cerebral vessels potently, an effect mediated by ETA receptors on the smooth muscle, although the subsequent signaling cascade is unclear. We tested whether the action of ET-I is mediated by the phospholipase C (PLC)/protein kinase C (PKC) cascade. Isometric force was measured in vitro in ring segments of rat basilar (BA) and middle cerebral (MCA) arteries and expressed as a percentage of the contraction to 124 mM K+. Concentration-effect curves for the constrictor effect of ET-1 (1 pM = 0.3 mu M) in control segments or after 25 minutes preincubation with an inhibitor of PLC (neomycin 100 mu M) or PKC (H7 10 mu M) were constructed under resting tone. In untreated BA, 100 nM ET-1 induced a contraction of 119 +/- 5.3% that fell significantly to 97 +/- 2.8% and 98 +/- 6.7% after neomycin or H7 pretreatment, respectively. In MCA, 100 nM ET-1 induced a contraction of 105 +/- 3.2% that fell significantly to 93 +/- 6.3% and 64 +/- 8.1% after neomycin or H7, respectively. There was no significant shift of the ET-1 EC50 after PKC inhibition in either vessel or PLC inhibition in BA. In summary, the amplitude of ET-1-induced contraction in cerebral vessels is reduced significantly, whereas the sensitivity to the agonist is unchanged, after blocking PLC with neomycin or PKC with H7. This indicates noncompetitive inhibition. ET-l-induced contraction in cerebral vessels thus depends on activation of the PLC/PKC cascade.