Human lymphatic vessel contractile activity is inhibited in vitro but not in vivo by the calcium channel blocker nifedipine

Abstract

Key pointsr We studied the effects of antihypertensive calcium channel blockers on Ca V 1.2, the predominantly expressed L-type calcium channel in the largest human lymphatic vessel, the thoracic duct.r Human lymphatic collecting vessels, both large and small, are highly-sensitive in vitro to calcium channel blockers; exposure to these drugs inhibits endogenous lymphatic contractile activity and action potentials and diminishes noradrenaline-induced phasic contractions.r In vivo administration of calcium channel blocker nifedipine to healthy volunteers did not reduce lymphatic contractile activity despite all subjects achieving nifedipine plasma concentrations comparable with those observed to affect contractile function in vitro.r These results indicate that calcium channel blocker-related oedema is unlikely to be exacerbated by an off-target effect of the drugs diminishing lymphatic pumping and fluid removal.Abstract Calcium channel blockers (CCB) are widely prescribed anti-hypertensive agents. The commonest side-effect, peripheral oedema, is attributed to a larger arterial than venous dilatation causing increased fluid filtration. Whether CCB treatment is detrimental to human lymphatic vessel function and thereby exacerbates oedema formation is unknown. We observed that spontaneous lymphatic contractions in isolated human vessels (thoracic duct and mesenteric lymphatics) maintained under isometric conditions were inhibited by therapeutic concentrations (nanomolar) of the CCB nifedipine while higher than therapeutic concentrations of verapamil (micromolar) were necessary to inhibit activity. Nifedipine also inhibited spontaneous action potentials measured by sharp microelectrodes. Furthermore, noradrenaline did not elicit normal increases in lymphatic vessel tone when maximal constriction was reduced to 29.4 ± 4.9% of control in the presence of 20 nmol l −1 nifedipine. Transcripts for the L-type calcium channel gene CACNA1C were consistently detected from human thoracic duct samples examined and the Ca V 1.2 protein was localized by immunoreactivity to lymphatic smooth muscle cells. While human lymphatics ex vivo were highly sensitive to nifedipine, this was not apparent in vivo when nifedipine was compared to placebo in a randomized, double-blinded clinical trial: conversely, lymphatic vessel contraction frequency was increased and refill time was faster despite all subjects achieving target nifedipine plasma concentrations. We conclude that human lymphatic vessels are highly sensitive to nifedipine in vitro but that care must be taken when extrapolating in vitro observations of lymphatic vessel function to the clinical situation, as similar changes in lymphatic function were not evident in our clinical trial comparing nifedipine treatment to placebo.

Mechanisms of Acute Alcohol Intoxication-Induced Modulation of Cyclic Mobilization of [Ca2+] in Rat Mesenteric Lymphatic Vessels

“…16,17 Our observations confirm that sarcolemmal Ca 2 + entry via L-type Ca 2 + channels contributes to the spontaneous Ca 2 + transients that precede lymphatic phasic contractions. Studies on mesenteric lymphatic vessels using wire myograph have shown that nifedipine in rats (10 -6 M) 16 and in humans (3 · 10 -9 M) 33 abolishes lymphatic pumping. Our findings with the lymphatic vessels isolated from rats that did not receive alcohol reflect the results of Atchison and Johnston, who used isolated bovine mesenteric lymphatic vessels and observed that nifedipine, applied at the same concentration we used, decreased both contraction frequency and amplitude of contraction.…”

Lymphatic Vessel Network Structure and Physiology

“…Using Tetrodotoxin (TTX), fast Na + channel inward current was shown to significantly contribute to the spontaneous action potentials initially in sheep mesenteric collecting lymphatics (445), and later in human mesenteric collecting lymphatics and thoracic duct, with Na v 1.3 as the predominantly expressed voltage-sensitive Na + channel (1062). However, in both humans and sheep there are some vessels that are resistant to TTX, in which voltage-gated Ca 2+ channels may be sufficient to produce action potentials (445, 1062), as blockade of L-type voltage-gated Ca 2+ channels can eliminate action potentials in collecting lymphatic vessels (1064, 1112). In bovine and guinea pig lymphatic vessels, TTX has not been found to block spontaneous contractions (47, 676, 1104).…”

“…The fast, initial repolarization may be due to an outward current caused by activation of K v channels (1061). L-type voltage-gated Ca 2+ channels, which open more slowly than the fast voltage-gated Na + channels, contribute to the plateau phase of cardiac action potentials, and are suspected to contribute to the depolarization and plateau phase in lymphatic smooth muscle (445, 1064). Recent work shows that the L-type voltage-gated Ca 2+ channel isoform Ca v 1.2 is expressed in lymphatic smooth muscle from rats (595) and humans (1064).…”

“…L-type voltage-gated Ca 2+ channels, which open more slowly than the fast voltage-gated Na + channels, contribute to the plateau phase of cardiac action potentials, and are suspected to contribute to the depolarization and plateau phase in lymphatic smooth muscle (445, 1064). Recent work shows that the L-type voltage-gated Ca 2+ channel isoform Ca v 1.2 is expressed in lymphatic smooth muscle from rats (595) and humans (1064). The Ca v 1.2 channel is the dominant Ca 2+ channel in cardiac muscle contraction (168), and appears to have the same role in lymphatic muscle (595).…”

Lymphatic pumping: mechanics, mechanisms and malfunction

“…LMC contractions depend predominantly on Ca 2+ influx through L‐type, voltage‐gated Ca 2+ channels (Telinius et al . c ), while the resting membrane potential is influenced substantially by Cl − (van Helden, ; von der Weid et al . b ) and voltage‐gated K + channels (Allen & McHale, ; Telinius et al .…”