After reading this chapter you should be able to:

outline the ultrastructural basis of vascular contraction (12.2);

contrast contraction in vascular and cardiac myocytes (12.1, 12.3);

outline the roles of Ca2+, K+ and Cl channels in vascular tone regulation (12.4);

state the roles of myosin light-chain kinase (MLCK), myosin light-chain phosphatase (MLCP), phospholipase C (PLC), inositol 1,4,5 trisphosphate (IP3) and diacylglycerol (DAG) in excitation-contraction coupling (12.3, 12.5);

explain the difference between depolarization-dependent and depolarization-independent contraction (12.5);

state the role and mechanism of Ca2+-sensitization during tonic contraction (12.5);

explain how sympathetic nerve activity evokes vasoconstriction (12.5);

outline four mechanisms mediating vasodilatation (12.7).