Inhibition of myosin light chain phosphorylation decreases rat mesenteric lymphatic contractile activity

Abstract

Based on the well-established finding that the phosphorylation of myosin light chain 20 (MLC20) plays an essential role in blood vessel smooth muscle contraction, we investigated if phosphorylated MLC20 (pMLC20) would modulate the tonic and/or phasic contractions of lymphatic muscle. The effects of ML-7, a MLC kinase inhibitor (1-10 M), were tested on the contractile parameters of isolated and cannulated rat mesenteric lymphatics during their responses to the known modulators, pressure (1-5 cmH2O) and substance P (SP; 10 Ϫ7 M). Immunohistochemical and Western blot analyses of pMLC20 were also performed on isolated lymphatics. The results showed that 1) increasing pressure decreased both the lymphatic tonic contraction strength and pMLC20-to-MLC20 ratio; 2) SP increased both the tonic contraction strength and phosphorylation of MLC20; 3) ML-7 decreased both the lymphatic tonic contraction strength and pMLC20-to-MLC20 ratio; and 4) the increase in lymphatic phasic contraction frequency in response to increasing pressure was diminished by ML-7; however, the phasic contraction amplitude was not significantly altered by ML-7 either in the absence or presence of SP. These data provide the first evidence that tonic contraction strength and phasic contraction amplitude of the lymphatics can be differentially regulated, whereby the increase in MLC20 phosphorylation produces an activation in the tonic contraction without significant changes in the phasic contraction amplitude. Thus, tonic contraction of rat mesenteric lymphatics appears to be MLC kinase dependent. ML-7; lymphatic contraction; tonic contraction; phasic contraction THE LYMPHATIC SYSTEM plays essential roles by returning the protein-rich interstitial fluid to the blood circulation for fluid homeostasis, transporting lipids and lipid-soluble vitamins absorbed from the intestines to the circulation for nutrition, and distributing immune cells to the lymph nodes for defense against diseases. All of these vital functions rely on the contractile activities of the muscle cells residing in the lymphatic vessel wall. The muscular lymphatic vessels are composed of many basic structural and functional units called lymphangions, which are capable of exhibiting intrinsic contractile activities to propel lymph flow through the network of the lymphatic vessels. Although the classical influence of pressure and flow on lymphatic contractility has been well documented (14 -16, 24, 31, 37, 38, 51), the molecular mechanisms regulating the contractile activities of the lymphatic muscle are not well understood.Cardiac muscles and most vascular smooth muscles (VSMs) exercise their physiological functions by phasic and tonic contractions, respectively, whereas lymphatic muscle accomplishes its functions using both tonic and phasic contractions. In general, an increase in the intracellular Ca 2ϩ concentration ([Ca 2ϩ ] i ) is the primary mechanism that initiates muscle contraction, a mechanism shared by striated muscles and VSMs. In striated muscle, Ca 2ϩ binding to troponin C in...

MicroRNA signature of inflamed lymphatic endothelium and role of miR-9 in lymphangiogenesis and inflammation

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Indocyanine Green and Lymphatic Imaging: Current Problems

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Reduction of contractility and reactivity in isolated lymphatics from hemorrhagic shock rats with resuscitation

“…Subsequently, we calculated these indices for the assessment of isolated lymphatic contractility as described previously [7][8][9] , including the TI, which refers to the preparing status of lymphatic subsequent contraction, CA, which refers to the normalized intensity of lymphatic contraction, FPF, which refers to the capacity of lymph transport. We found that hemorrhagic shock lead a decrease in CF, TI, and FPF of isolated lymphatics from thoracic duct, suggesting a reduction of lymphatic contractility.…”

“…Finally, the contractility of isolated lymphatics was evaluated with the following indices as described previously [7][8][9] . …”