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. 2015 Aug;146(2):129–132. doi: 10.1085/jgp.201511468

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© 2015 Tykocki and Nelson

This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 3.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/3.0/).

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Figure 1. — Arrangement of microdomains within a theoretical smooth muscle cell regulates myogenic tone. As modeled by Karlin (2015), myogenic tone development is regulated by the crosstalk between pro-contractile and pro-relaxant mechanisms that exist in close proximity within the smooth muscle cell. In the correct spatial arrangement, nonselective cation channels in stretch-sensing microdomains on the cell wall respond to deformation caused by increases in intraluminal pressure, allowing influx of Na⁺ (NSC_Na) and Ca²⁺ (NSC_Ca). This leads to CaCC (Cl_Ca) opening, depolarization of the cell membrane (+V_M), and opening of VDCCs (Ca_V). In close proximity to stretch-sensing microdomains are pro-relaxant microdomains, formed at the interface between the junctional sarcoplasmic reticulum and the plasma membrane and containing RyRs and BK channels (BK). Increases in cytosolic Ca²⁺ cause RyR-mediated Ca²⁺ sparks that open BK channels to hyperpolarize the cell (−V_M).