ABSTRACT
Variety is not only the ‘‘spice of life’’; it is also intrinsic to the normal functioning of all vascular beds in the body. All blood vessels have certain common features, but closer examination reveals important regional variations in structure and function. This diversity exists not only between vessels of different vascular beds but also between large and small arteries within a single organ. Indeed, cellular electrophysiology has revealed that the medial layer of the arterial wall is not homogeneous but instead is composed of a mosaic of electro physiologically diverse smooth muscle cells (SMCs). Different levels of expression and types of ion channels may contribute to this electrical heterogeneity within a single type of blood vessel. On a larger scale, the heterogeneity of ion channels between vascular beds may partly explain the site-specific responses of different arteries to vasoactive stimuli including altered oxygen tension and pH. Further diversity of ion channel expression has been noted during conditions of
cardiovascular disease, in which the abnormal expression and possibly properties of ion channels may establish pathological levels of excitability in the affected SMCs. For example, in both pulmonary and systemic hypertension there is a characteristic loss of Kþ channel function and expression in the SMC membranes, causing membrane depolarization and predisposing the affected arteries to vasoconstriction and vascular remodeling.
