ET‐1‐associated vasomotion and vasospasm in lymphatic vessels of the guinea‐pig mesentery

Abstract

In vitro experiments were performed to investigate the actions of endothelin‐1 (ET‐1) on vasomotion and vasospasm in guinea‐pig mesenteric lymphatics. ET‐1 modulated lymphatic vasomotion independent of the endothelium, with lower concentrations (10 nM) increasing lymphatic vasomotion and higher concentrations (100 nM) causing vasospasm. ET‐1‐induced increases in vasomotion were accompanied by an increase in tonic [Ca²⁺]_i. These actions were inhibited by the ET_A receptor antagonist BQ‐123 (1 μM), the phospholipase C (PLC) inhibitor U73122 (5 μM), removal of extracellular Ca²⁺, chelation of intracellular Ca²⁺ with BAPTA/AM (10 μM), the store Ca²⁺‐ATPase inhibitor thapsigargin (1 μM), caffeine (10 mM) and the inositol 1,4,5‐trisphosphate (IP₃) receptor blocker heparin and 2‐APB (30 μM). In contrast, the ET_B receptor antagonist BQ‐788 (1 μM), ryanodine (1 & 20 μM), pertussis toxin (PTx) or Cs⁺ had no significant actions on vasomotion or the magnitude of increase in tonic [Ca²⁺]_i. ET‐1‐induced vasospasm was accompanied by a transient increase in smooth muscle [Ca²⁺]_i followed by a sustained plateau, an action that was abolished by removal of extracellular Ca²⁺, but only marginally inhibited by nifedipine (1 μM). Caffeine (10 mM), SKF 96165 (30 μM) or U73122 (5 μM) together with nifedipine (1 μM) abolished ET‐1‐induced vasospasm and increase in [Ca²⁺]_i. These results indicate that ET‐1 increases lymphatic vasomotion by acting on smooth muscle ET_A receptors and activation of G‐protein‐PLC‐IP₃ cascade, which is known to cause pacemaker Ca²⁺ release and resultant pacemaker potentials. High concentrations of ET‐1 cause a failure in Ca²⁺ homeostasis causing vasospasm, triggered by excessive Ca²⁺ influx primarily through store‐operated channels (SOCs) with L‐Ca²⁺ voltage‐operated channels (VOCs) also contributing, but to a much lesser extent. British Journal of Pharmacology (2003) 140, 1399–1413. doi:10.1038/sj.bjp.0705573