Review article: lymphatic vessel pumping and inflammation--the role of spontaneous constrictions and underlying electrical pacemaker potentials.

The lymphatic circulation is important in maintaining tissue fluid homeostasis. It removes fluid, proteins and other particles from tissue spaces and returns them to the blood stream. This function is achieved by rhythmical contractions of the collecting lymphatic vessels. The contractile mechanism is intrinsic to the smooth muscles present in the vessel wall and consequent to action potentials. The underlying electrical mechanism has been proposed to be due to rhythmic synchronization of Ca2+-dependent spontaneous transient depolarizations. The lymphatic pumping activity adapts to changes in fluid load and has been observed to augment during inflammatory reactions to help resolve the associated oedema. This beneficial action has been generally attributed to the increase in interstitial pressure consequent to the oedema. However, little attention has been paid to the possible role inflammatory mediators that are present in the lymphatic vessel environment, could play in directly affecting the lymphatic contractile mechanism. This review article discusses our current knowledge on the mechanism and initiation of lymphatic pumping and how these events are modulated during inflammatory conditions.