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 +/- 0.5 mV (n = 100) which was significantly different from the value of -60.8 +/- 1.1 mV (n = 75) recorded in smooth muscle. 3. Acetylcholine (ACh, 5-10 microM) generally evoked an initial hyperpolarization followed by depolarization (mean 3.4 +/- 0.5 mV and 15.4 +/- 1.0 mV, respectively, n = 75). 4. Ca(2+)-activated K+ channels were likely to underlie the ACh-induced hyperpolarization as this response exhibited an increased 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 N omega-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.
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