{'fraction_non_alphanumeric': 0.04137235116044399, 'fraction_numerical': 0.02472250252270434, 'mean_word_length': 5.177570093457944, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Decreased endothelin binding and [Ca2+]i signaling in microvessels of DOCA-salt hypertensive rats

Objectives and design The deoxycorticosterone acetate (DOCA)-salt model of hypertension is characterized by elevated vascular endothelin-1 (ET-1) and by reduced contraction to ET-1 in isolated mesenteric small arteries. The decreased contraction to ET-1 may be a compensatory mechanism caused by elevations in ET-1 and arterial pressure. The present study was designed to determine whether down-regulation of endothelin receptors or altered Ca2+ signaling contribute to the decreased contraction to ET-1. Methods and results Contraction to ET-1 (10−11 to 10−8 mol/l) was significantly reduced in isolated mesenteric small arteries (87–286 μm intraluminal diameter) from DOCA-salt rats compared with placebo rats. Membrane protein was obtained for measurement of [125I]ET-1 receptor binding and ETA receptor expression. Maximum binding was significantly reduced in vascular membranes from DOCA-salt rats (670 ± 71 fmol/mg protein) compared with placebo rats (1165 ± 75 fmol/mg protein), but binding affinity was unchanged. Conversely, ETA receptor protein was increased in DOCA-salt rat vessels. To assess Ca2+ signaling, freshly dissociated mesenteric small artery smooth muscle cells were loaded with fura-2 for measurement of the average myoplasmic free Ca2+ concentration ([Ca2+]i). The ET-1 (10−9 mol/l) induced increase in [Ca2+]i was significantly less in cells from DOCA-salt rats compared with from placebo rats. This effect was not due to a loss of L-type Ca2+ channels since expression was increased in membrane protein from DOCA-salt rats compared with placebo rats, as measured by Western blot analysis. Conclusions These findings indicate that decreases in receptor binding and Ca2+ signaling contribute to the impaired contraction to ET-1 in DOCA-salt hypertensive rats. However, these changes are not due to reduced expression of ETA receptors or L-type Ca2+ channels.