Elastase-Induced Suppression of Endothelin-Mediated Ca ²⁺ Entry Mechanisms of Vascular Contraction

Abstract

Abstract-Abdominal aortic aneurysm (AAA) is associated with increased endothelin (ET-1), both systemically and locally in the aorta. Also, elastase activity is increased in human AAA, and elastase perfusion of the aorta induces aneurysm formation in animal models of AAA. However, whether elastase directly affects the ET-1-induced mechanisms of aortic smooth muscle contraction is unclear. Isometric contraction and 45 Ca 2ϩ influx were measured in aortic strips isolated from male Sprague-Dawley rats and treated with elastase (5 U/mL). To avoid degradation of the extracellular matrix proteins by elastase, experiments were performed in the presence of elastin (10 mg/mL). In normal Krebs solution (2.5 mmol/L Ca 2ϩ ), ET-1 (10 Ϫ7 mol/L) caused contraction of aortic strips that was inhibited by elastase (5 U/mL). The elastase-induced inhibition of ET-1 contraction was slow in onset (4.6Ϯ0.4 minutes), time-dependent, complete in 34Ϯ3 minutes, and reversible. In Ca 2ϩ -free Krebs solution, caffeine (25 mmol/L) caused a small contraction that was not inhibited by elastase, suggesting that elastase does not inhibit Ca 2ϩ release from the intracellular stores. Membrane depolarization by 96 mmol/L KCl, which stimulates Ca 2ϩ entry from the extracellular space, caused a contraction that was inhibited by elastase in a concentration-dependent, time-dependent, and reversible fashion. The reversible inhibitory effects of elastase, particularly in the presence of elastin, suggest that they are not due to dissolution of the extracellular matrix or smooth muscle contractile proteins. Elastase also inhibited ET-1 and KCl-induced

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“…This may possibly be the result of the simultaneous releasing effect of Ac.nHexane on the Ca +2 stores that interfere with the relaxant effect because high K + in the medium induces Ca +2 influx through VDCs, which further activates Ca +2 -induced Ca +2 release through the ryanodine receptor. [35][36][37] To test this speculation, Ac.nHexane was studied for its possible vasoconstrictor effect in Ca +2 -free medium. When tested on the baseline tension, Ac.nHexane exhibited a modest contractile effect.…”

O-GlcNAcylation: a novel pathway contributing to the effects of endothelin in the vasculature

“…Inositol 1,4,5-trisphosphate acts on specific receptors on the intracellular Ca 2ϩ stores and stimulates Ca 2ϩ release (109). ET-1 also activates plasma membrane Ca 2ϩ channels and stimulates Ca 2ϩ influx (23,147). ET-1-induced increase in DAG stimulates PKC activity (73,106,146).…”

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“…IP 3 acts on specific receptors on the intracellular Ca 2+ stores and stimulate Ca 2+ release [51]. ET also activates plasma membrane Ca 2+ channels and stimulates Ca 2+ influx from the extracellular space [55,56]. The ET-induced increase in diacylglycerol stimulates PKC activity [57][58][59].…”