Figure 50-11
Mechanisms of calcium sensitization in vascular smooth
muscle. Sensitization ultimately results from increased functional activity of either
of the contractile proteins actin or myosin. Actin can be modulated by a number
of actin-regulating proteins (1). Myosin activity is determined by its degree of
phosphorylation. Myosin light chain (MLC) phosphorylation can be increased by inhibiting
the mechanisms responsible for dephosphorylation (i.e., inhibiting MLC phosphatase
activity) (2). This can occur either directly or indirectly. It can also be increased
by increasing the activity of MLC kinase. The latter can occur as a result of inhibiting
the breakdown of MLC kinase (3) or as a result of calmodulin activity (4). P, phosphorylation;
MLCKa
, active myosin light chain kinase; MLCKi
, inactive myosin
light chain kinase.
