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Vascular smooth muscle cell
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The vascular smooth muscle cell is the one that forms the muscular layer in the walls of the arteries and veins. There it plays a decisive role: by narrowing or widening the caliber of the vessel, it regulates blood pressure and how much oxygen reaches the tissues.
Its contraction is switched on by calcium. When calcium enters the cell it binds to calmodulin, a protein that senses it; activated calmodulin turns on an enzyme called myosin light chain kinase; and from there the cross-bridge cycle starts, the repeated attaching and detaching of the two proteins that generate force inside the cell, myosin and actin.
The way it contracts is distinctive. It is involuntary, it does not depend on any decision to move, and it is slow: its ATPase activity, the rate at which it burns cellular energy, is much lower than that of skeletal muscle, the muscle that moves the arms and legs. The trade-off is that it holds the contraction much longer. This is not a muscle of quick tugs: it squeezes and does not let go.
In brief
The vascular smooth muscle cell sits in the wall of arteries and veins and regulates blood pressure and tissue oxygenation.
Its contraction depends on calcium: calcium binds calmodulin, which activates myosin light chain kinase and sets off the cross-bridge cycle.
It contracts involuntarily and slowly, with far lower ATPase activity than skeletal muscle, but it holds the contraction longer.
This is not a muscle of quick tugs: it squeezes and does not let go.
Sources (2)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Smooth Muscle, StatPearlsPublished
- National Center for Biotechnology Information, StatPearls PublishingAnatomy, Smooth Muscle, StatPearlsPublished
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