Diversity of phenotype and function of vascular smooth muscle cells.

Recent observations indicate that cell-to-cell and segment-to-segment variation occur in the morphology and function of vascular smooth muscle (VSM) cells in pulmonary and systemic arteries. This diversity includes differences in cell phenotype and in expression of cytoskeletal proteins as well as heterogeneity of the number and activity of potassium (K) channel types. The concept of cell diversity indicates that the arterial media is a mosaic of cell populations that differ from each other in phenotype and function. The prevalence of various VSM populations varies from segment to segment within a single artery and also may contrast among vascular trees of different organs. The composition of the arterial media is plastic, changing with normal development from fetus to adult and in response to vascular injury. Diversity of cell function is important in physiology and pathophysiology, allowing localized responses to vasodilators, vasoconstrictors, and proliferative stimuli within a vascular segment. Diversity may also explain the divergent responses of vascular beds to a common stimulus, such as hypoxia.