Depolarization of collecting lymphatic endothelium with acetylcholine or TRPV4 activation

Abstract

Smooth muscle cells of collecting lymphatic vessels undergo coordinated contractions to propel lymph centrally. Whether endothelial‐derived hyperpolarization [via activation of small‐ and intermediate‐conductance Ca2+ activated K+ channels (SKCa/IKCa)] shown in blood vessels is manifest in governing lymphatic function has not been established. To test this possibility, lymphangions dissected from mouse popliteal fossae were treated to yield intact lymphatic endothelial cell tubes (LECTs; width: ~50μm; length: ~500 μm) for intracellular recording (bath pH 7.4; 30°C). Resting membrane potential (Vm) of LECTs was −60±5 mV and depolarized (P<0.05) to −49±5 mV with BaCl2 (100 μM; n=6). Activation (NS309, 1 μM) or blockade [apamin (300 nM) + charybdotoxin (100 nM)] of SKCa/IKCa did not alter Vm (n=4). Acetylcholine (ACh, 1 μM) or GSK (TRPV4 channel agonist; 100 nM) depolarized LECTs by 29±7 and 49±4 mV, respectively (P<0.05; n=4 each). Thus blockade of inward‐rectifying K+ channels and agents promoting Ca2+influx (via TRPV4) as well as release from the endoplasmic reticulum (ACh) evoke LECT depolarization that is facilitated by lack of functional SKCa/IKCa expression. With myoendothelial coupling, endothelium‐derived depolarization may coordinate contraction of lymphatic smooth muscle cells and thereby determine the effectiveness of lymph transport. (NIH R37HL041026, R01HL086483, F32HL110701, R01HL089784)