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

Abstract

Key pointsr Initial studies have described the electrical properties of lymphatic smooth muscle cells from different animal species and the ion channels contributing to these properties. However, there is a translational gap to the human situation where studies on human tissue are lacking.r Voltage-gated sodium channels are essential for the generation of action potentials, and thus spontaneous contractions in human lymphatic vessels, but not noradrenaline-induced contractions. A sodium channel opener elicited contractions as a result of calcium influx via voltage-gated calcium channels and the sodium-calcium exchanger.r Pharmacological characterization and the mRNA expression profile indicate that Na v 1.3 is the most prevalent sodium channel.r These results provide support for an important role of sodium channels in spontaneous human lymphatic vessel electrical activity and contractility.Abstract 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 the present study, we report the electrical activity and APs 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 TTX inhibited spontaneous contractions in six of 10 spontaneously active vessels, whereas ranolazine, which has a narrower VGSC blocking profile, had no influence on spontaneous activity. TTX did not affect noradrenaline-induced contractions. The VGSC opener veratridine induced contractions in a concentration-dependent manner (0.1-30 μM) eliciting a stable tonic contraction and membrane depolarization to −18 ± 0.6 mV. Veratridine-induced depolarizations and contractions were reversed ß80% 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 Na V 1.3 to be the predominantly expressed VGSC isoform. Electrophysiology of mesenteric lymphatics determined the resting membrane potential to be −45 ± 1.7 mV. Spontaneous APs were preceded by a slow depolarization of 5.3 ± 0.6 mV after which a spike was elicited that almost completely repolarized before immediately depolarizing again to plateau. Vessels transiently hyperpolarized prior to returning to the resting membrane potential. TTX application blocked APs. We have shown that VGSC are necessary for initiating and maintaining APs and spontaneous contractions in human lymphatic vessels and our data suggest the main contribution from comes Na V 1.3. We have also shown that activation of these channels augments the contractile activity of the vessels.

Lymphatic Vessel Network Structure and Physiology

“…Like vascular smooth muscle, cytoplasmic Ca 2+ and the sensitivity of contractile molecules to Ca 2+ are key factors. Collecting lymphatic vessels are very sensitive to changes in extracellular Ca 2+ , such that lymphatic contractions cease fairly quickly in Ca 2+ -free bathing solutions and also if the Ca 2+ concentration is too high (245, 671, 1007, 1062). Voltage-gated L-type Ca 2+ channels appear to have a predominant role in Ca 2+ entry into lymphatic muscle cells, as drugs that block these channels inhibit the ability of lymphatics to contract (42, 595, 1005, 1062).…”

“…29) (1062). There is a one-to-one relationship between action potentials and phasic contractions (25).…”

“…A separate paper from the same group reported that upstretched rat mesenteric lymphatic vessels typically had a Vm between −65 to −55 mV (mean ± SEM 61 ± 2 mV) while the range for vessels on a wire myograph was from −45 to −35 mV, with an average ± SEM of −39 ± 2 mV (595). In stretched human thoracic duct and mesenteric collecting lymphatics the V m was reported to typically be at or near −45 mV (1062). For comparison, lymphatic endothelium in guinea pig mesenteric collecting lymphatics was reported to be more negative, with an average ± SEM of −71.5 ± 0.5 mV (1116).…”

Effect of lidocaine with and without epinephrine on lymphatic contractile activity in mice in vivo

“…[19] demonstrated that the topical application of the local anesthetic lignocaine (10%) in rats slowed lymph flow, mainly due to blockage of nerve-mediated action potentials. It was also reported that lidocaine at a concentration of 0.3μM reduced the spontaneous contractile activity in human mesenteric lymphatic vessel segments [20]. Lidocaine blocks a broad spectrum of voltage-gated sodium channels (VGSCs), whereas tetrodotoxin (TTX) blocks specific VGSC subtypes, which are also known to inhibit lymphatic contractility [20].…”

“…It was also reported that lidocaine at a concentration of 0.3μM reduced the spontaneous contractile activity in human mesenteric lymphatic vessel segments [20]. Lidocaine blocks a broad spectrum of voltage-gated sodium channels (VGSCs), whereas tetrodotoxin (TTX) blocks specific VGSC subtypes, which are also known to inhibit lymphatic contractility [20]. …”