Functional electrical properties of the endothelium in lymphatic vessels of the guinea‐pig mesentery

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Abstract
1 The resting and agonist-stimulated properties of endothelial cells and electrical communication between the endothelium and smooth muscle were investigated in open segments of guinea-pig mesenteric lymphatic vessels using intracellular microelectrodes. 2 Endothelial cells had a mean resting membrane potential (RMP) of – 71.5 ± 0.5mV (n= 100) which was significantly different from the value of −60.8 ± 1.1 mV (n= 75) recorded in smooth muscle. 3 Acetylcholine (ACh, 5–1 μm) generally evoked an initial hyperpolarization followed by depolarization (mean 3.4 ± 0.5 mV and 15.4 ± 1.0 mV, respectively, n= 75). 4 Ca2+-activated K+ channels were likely to underlie the ACh-induced hyperpolarization as this response exhibited an increase in membrane conductance, was larger in 0.5 mm K+ solution and was blocked by charybdotoxin (50 nm). 5 The endothelium did not exhibit a response to nitric oxide (NO) as the NO-donor sodium nitroprusside did not alter the RMP and the electrical responses to ACh were not affected by the NO-synthase inhibitor Nω-nitro L-arginine at a concentration which markedly inhibited smooth muscle hyperpolarization. 6 Electrical coupling between the endothelium and smooth muscle was not functional as there was extremely limited electrical continuity (1 in 12, endothelial/smooth muscle cell simultaneous recordings) and bradykinin, noradrenaline and isoprenaline caused different electrical responses in the two cell types. 7 These results provide the first description of RMP and electrical responses to various agonists in the lymphatic endothelium and its lack of functional electrical coupling with the smooth muscle.