**1. Introduction**

The vascular system, which includes an extensive network of arteries, capillaries, and veins, exhibits specific biochemical, cellular, and transport functions. The absorption of essential nutrients and removal of cellular metabolic products both depend on the vasculature [1]. The vessel wall is an intricate structure composed of three layers: the intima, media, and externa. The homeostasis of the vascular system depends on the consistent function of each layer. The thinnest constituent layer is the intima, which consists of a single layer of endothelial cells (ECs) on a basement membrane. Although ECs are typically flat, they are plump or cuboidal in venules composed of numerous endothelial cells [2]. Endothelial cells perform critical functions in all aspects of tissue homeostasis; in addition, they regulate vascular tone by interacting with components of the peripheral nervous system and are related to inflammatory and immunological processes [3, 4]. The media mainly contains smooth muscle cells (SMCs) and elastic fibers. Elastic fibers are mainly a source of structural support, while SMCs play a vital role in maintaining the vascular structure, vascular repair, remodeling, and disease. VSMCs exhibit extraordinary plasticity and undergo remodeling in response to local hemodynamic changes, mechanical forces, hormones, and cytokines [5, 6]. The most remarkable functions of VSMCs are to regulate vascular tone and vessel diameter, which determines blood pressure and tissue perfusion. Some components of vascular contractility, such as the actin cytoskeleton, are required for VSMC proliferation and migration. Circular

RNA, microRNA, and some other transcription factors jointly regulate the expression of smooth muscle α-actin (α-SMA) and the contraction of VSMCs [7, 8]. The outer most layer of the vessel wall is the adventitia. In vertebrates, the adventitia is important because the fibroelastic connective tissue stroma is an important structural component of all tissues. The adventitial stroma contains an extracellular matrix scaffold including fibroblasts, blood and lymphatic vessels, nerve endings, progenitor cells, and immune cells. In one sense, the adventitia is the most complex and heterogeneous compartment of the vessel wall [9].

Ion channels play an important role in the mechanism of action of vasodilators and vasoconstrictors that modulate vascular tone and the effects of disease states, such as hypertension, obesity, and diabetes, which depend on ion channel expression and function. We focus on the basic properties, physiological functions, regulation, and pathological alterations in major classes of K+ channels that have been detected in VSMCs and/or ECs, including Ca2+-activated K+ channels, ATPsensitive K<sup>+</sup> channels, and voltage-gated K+ channels.
