Voltage-gated sodium channels contribute to action potentials and spontaneous contractility in isolated human lymphatic vessels

Voltage-gated sodium channels (VGSC) play a key role for initiating action potentials (AP) in excitable cells. VGSC in human lymphatic vessels have not been investigated. In this study we describe the electrical activity and action potentials of small human lymphatic collecting vessels as well as mRNA expression and function of VGSC in small and large human lymphatic vessels. The VGSC blocker tetrodotoxin (TTX) inhibited spontaneous contractions in six of ten spontaneously active vessels whereas ranolazine, which has a narrower VGSC blocking profile, had no influence on spontaneous activity. Tetrodotoxin did not affect noradrenaline-induced contractions. The VGSC opener veratridine induced contractions in a concentration-dependent manner (0.1-30μM) eliciting a stable tonic contraction and membrane depolarisation to -18 ± 0.6 mV. Veratridine-induced depolarisations and contractions were ≈80% reversed by TTX, and were dependent on Ca(2+) influx via L-type calcium channels and the sodium-calcium exchanger in reverse mode. Molecular analysis determined NaV 1.3 to be the predominantly expressed VGSC isoform. Electrophysiology of mesenteric lymphatics determined resting membrane potential (RMP) to be -45 ± 1.7 mV. Spontaneous APs were preceded by a slow depolarisation of 5.3 ± 0.6 mV after which a spike was elicited, which almost completely repolarised before immediately depolarising again to plateau. Vessels transiently hyperpolarized prior to returning to RMP. TTX application blocked APs. We have shown that VGSC are necessary for initiating and maintaining action potentials and spontaneous contractions in human lymphatic vessels and our data suggest the main contribution from comes NaV 1.3. We have furthermore shown that activation of these channels augment the contractile activity of the vessels. This article is protected by copyright. All rights reserved.