Lymphatic vasomotion.

1. Experimental findings in the past decade have greatly advanced present understanding of electrical/mechanical rhythmicities in smooth muscle, including vasomotion. Lymphatic vessels show strong vasomotor activity and have provided a key experimental system to study these processes. 2. Evidence from lymphatic vessels, blood vessels and other smooth muscles indicates that rhythmical contractions arise through a Ca2+ store-controlled pacemaker mechanism, which can function to cause smooth muscle constriction. 3. Such a model fits with observations that vasomotion can be near synchronous over large vessel lengths involving many cells. 4. The alternative interpretation that smooth muscle rhythmicities are generated by a cardiac-like electrical pacemaker mechanism has not been substantiated in any smooth muscle preparation under normal physiological conditions. However, elements of this latter mechanism are likely to be present at least in some smooth muscles, serving to modulate pacemaking.