FIGURE 6. Sublocalization of calcium-activated potassium channels in the vascular wall.

FIGURE 6

Sublocalization of calcium-activated potassium channels in the vascular wall. The three subtypes of calcium-activated potassium channels of large (BKCa), intermediate (IKCa) and small conductance (SKCa) are present in the vascular wall but with very specific cellular and subcellular localization. BKCa channels are expressed preferentially in discrete vascular smooth muscle area, smooth muscle plasmerosome, associated with endoplasmic reticulum. They form signal complexes with canonical or vanilloid transient receptor potential channels 1 (TRPC1 or TRPV4). The IKCa and SKCa channels (especially the SK3 α subunit) are constitutively expressed in endothelial cells. SKCa are diffusely distributed over the plasma membrane with preferential locations at sites of homocellular endothelial gap junctions and caveolin-rich domains and are associated with various connexins (Cx) (endothelial caveolae). IKCa are preferentially localized within the endothelial projections through the internal elastic lamina (myoendothelial gap junctions). The activation of endothelial receptors and the shear stress exerted by the flowing blood increase endothelial [Ca2+]i. and activates endothelial NO-synthase (eNOS) as well as SKCa and IKCa channels. The subsequent endothelial hyperpolarization favors the entry of calcium as a positive feedback loop. The hyperpolarization can be conducted through myoendothelial gap junctions composed of Cx40 and possibly Cx37 to the underlying vascular smooth muscle. Additionally, accumulation of potassium ions in the intercellular space can hyperpolarize the smooth muscle cells by activating Na+/K+-ATPase and inwardly rectifying potassium channels (KIR). EC: endothelial cells; VSMC: vascular smooth muscle cells; ACh: acetylcholine; BK: bradykinin; SP: substance P; PE: phenylephrine; RyR: ryanodine receptor; CaV: voltage-activated calcium channels.

From: Chapter 1, Endothelium-Dependent Hyperpolarizations: The Classical “EDHF” Pathway

Cover of The Endothelium
The Endothelium: Part 2: EDHF-Mediated Responses “The Classical Pathway”.
Félétou M.
Copyright © 2011 by Morgan & Claypool Life Sciences Publisher.

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