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

Abstract

1 In vitro experiments were performed to investigate the actions of endothelin-1 (ET-1) on vasomotion and vasospasm in guinea-pig mesenteric lymphatics. 2 ET-1 modulated lymphatic vasomotion independent of the endothelium, with lower concentrations (p10 nM) increasing lymphatic vasomotion and higher concentrations (X100 nM) causing vasospasm. 3 ET-1-induced increases in vasomotion were accompanied by an increase in tonic [Ca 2 þ ] i . 4 These actions were inhibited by the ET A receptor antagonist BQ-123 (1 mM), the phospholipase C (PLC) inhibitor U73122 (5 mM), removal of extracellular Ca 2 þ , chelation of intracellular Ca 2 þ with BAPTA/AM (10 mM), the store Ca 2 þ -ATPase inhibitor thapsigargin (1 mM), caffeine (10 mM) and the inositol 1,4,5-trisphosphate (IP 3 ) receptor blocker heparin and 2-APB (30 mM). In contrast, the ET B receptor antagonist BQ-788 (1 mM), ryanodine (1 & 20 mM), pertussis toxin (PTx) or Cs þ had no significant actions on vasomotion or the magnitude of increase in tonic [Ca 2 þ ] i . 5 ET-1-induced vasospasm was accompanied by a transient increase in smooth muscle [Ca 2 þ ] i followed by a sustained plateau, an action that was abolished by removal of extracellular Ca 2 þ , but only marginally inhibited by nifedipine (1 mM). 6 Caffeine (10 mM), SKF 96165 (30 mM) or U73122 (5 mM) together with nifedipine (1 mM) abolished ET-1-induced vasospasm and increase in [Ca 2 þ ] i . 7 These results indicate that ET-1 increases lymphatic vasomotion by acting on smooth muscle ET A receptors and activation of G-protein-PLC-IP 3 cascade, which is known to cause pacemaker Ca 2 þ release and resultant pacemaker potentials. High concentrations of ET-1 cause a failure in Ca 2 þ homeostasis causing vasospasm, triggered by excessive Ca 2 þ influx primarily through store-operated channels (SOCs) with L-Ca 2 þ voltage-operated channels (VOCs) also contributing, but to a much lesser extent.

Mechanisms of Acute Alcohol Intoxication-Induced Modulation of Cyclic Mobilization of [Ca2+] in Rat Mesenteric Lymphatic Vessels

“…Although IP 3 -operated Ca 2 + stores play an important role in lymphatic vessel contraction in response to vasoconstrictor stimulation, 20,35,36 in our studies, IP 3 receptor-mediated Ca 2 + release from the SR did not significantly alter Ca 2 + transients or contraction frequency in lymphatic vessels from controls or alcohol-treated animals. Moreover, our results suggest that alcohol-induced changes in Ca 2 + transients are not due to a modification of IP 3 -mediated mobilization of Ca 2 + .…”

“…This increase in Ca 2 + was likely in consequence of RyR activation, as it was abolished following treatment with 20 mM of ryanodine. 35 In our studies, caffeine discontinued lymphatic vessel pumping in both the AAI and control groups. In addition, prior to lymphatic pumping cessation there was a single phasic contraction and associated Ca 2 + transient in the lymphatic vessels, which was significantly greater in the AAI group.…”

“…To our knowledge, no other studies have made this observation. 20,28,35,36 Possible explanations for this difference in results include differences in animal species, lymphatic preparations, concentration of the drug, and the pre-stimulation with constricting agents prior to use of the IP 3 R antagonist.…”

Calcium sensitivity and cooperativity of permeabilized rat mesenteric lymphatics

“…The pCatension relationship was normalized to the tension produced in pCa 4.5, then fitted to the Hill equation using nonlinear regression analysis to derive pCa50 (Ca 2ϩ concentration resulting in 50% maximal contraction) and Hill coefficient (nH; slope of the linear portion of the pCa-tension curve that represents cooperative activation) using Prism software. An independent sample t-test was used to determine differences in maximal tension, pCa 50 and nH between ␣-toxin-and ␤-escin-permeabilized lymphatics, and between ␣-toxin-permeabilized lymphatics and arteries or veins. Significance was set at P Ͻ 0.05.…”

“…This combination of smooth and striated muscle contractile elements present in lymphatic muscle could provide unique contractile characteristics (i.e., Ca 2ϩ sensitivity and cooperativity) for lymphatic myofilaments. Although numerous mechanical (3,12,30,35,49) and neurohumoral (1,2,19,31,46,50) factors have been shown to modulate the tonic and phasic activity of collecting lymphatics, few investigations of the basic contractile properties of the lymphatic myofilament have been published.…”