Myosin light chain phosphatase: it gets around.

The importance of Ca 2 /calmodulin-dependent myosin light chain kinase (MLCK) for smooth muscle contraction is well documented.1 Until recently, myosin light chain (MLC) phosphatase was thought to be unregulated and constitutively active. However, studies have demonstrated that smooth muscle contraction is dependent on regulation of MLC phosphatase activity.2,3 The inhibition of phosphatase activity increases force at a constant [Ca ], whereas a stimulation of MLC phosphatase activity reduces force at a constant [Ca ].