The mechanism of endothelin-1-mediated constriction in mesenteric arteries from rats with simulated sleep apnea.

摘要

Intermittent hypoxia/hypercapnia (IH/HC) to simulate sleep apnea in rats results in a significant elevation in mean arterial blood pressure (MAP), increased production of endothelin-1 (ET-1), and augmented constrictor sensitivity to ET-1 in resistance mesenteric arteries when compared to Sham (normoxic/normocapnic) rats. ET-1 signals through ETA receptors found on vascular smooth muscle cells (VSMC) resulting in contraction. ET-1-mediated constriction in IH/HC and Sham arteries was reversed with a selective ETA receptor antagonist, BQ123, which inhibited constriction ex vivo and decreased IH/HC rats MAP in vivo. Further investigation into ET-1-mediated constriction in IH/HC mesenteric arteries showed that the augmented constrictor response was not accompanied by an increase in intracellular calcium ([Ca2+]i), suggesting constriction is due to greater Ca2+-sensitization rather than changes in influx of Ca 2+ in the VSMC. Two major pathways of Ca2+-sensitization were examined: RhoA/associated kinase (ROK) and protein kinase C (PKC). Arteries from Sham rats were insensitive to ROK inhibition while IH/HC arteries minimally reduced ET-1-mediated constriction with ROK inhibition [Y-27632 (3 muM) and HA-1077 (10 muM)]. ET-1-meditated constriction was completely blocked with a myosin light chain kinase (MLCK) inhibitor, ML-9 (100 muM), in both Sham and IH/HC arteries. A general PKC inhibitor, GF-109203x (3 muM), greatly inhibited ET-1-induced constriction in IH/HC but not in Sham arteries, suggesting ET-1 signals almost exclusively through PKC in IH/HC arteries. Selective PKC inhibitors were used to discriminate the classes involved in ET-1-mediated constriction. Classical PKC (cPKC) isoforms were inhibited by Go6976 (1 muM) and did not affect ET-1-mediated constriction in either Sham or IH/HC arteries. Inhibition of novel PKC, PKCdelta, with rottlerin (3 muM) significantly reduced ET-1-mediated constriction IH/HC arteries but did not affect constriction in Sham arteries. PKCdelta was basally expressed in the membrane rather than cytosol in arteries from both IH/HC and Sham rats and ET-1 (10-8 mol/L) stimulation caused no further translocation. In conclusion, these data suggest that resistance arteries from IH/HC exposed rats are more sensitive to ET-1-mediated constriction than are Sham arteries and this is mediated through augmented PKCdelta signaling.