A single luminally continuous sarcoplasmic reticulum with apparently separate Ca2+ stores in smooth muscle

McCarron, J.G. and Olson, Marnie (2008) A single luminally continuous sarcoplasmic reticulum with apparently separate Ca2+ stores in smooth muscle. Journal of Biological Chemistry, 283 (11). pp. 7206-7218. ISSN 1083-351X (https://doi.org/10.1074/jbc.M708923200)

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Abstract

Whether or not the sarcoplasmic reticulum (SR) is a continuous, interconnected network surrounding a single lumen or comprises multiple, separate Ca2+ pools was investigated in voltage-clamped single smooth muscle cells using local photolysis of caged compounds and Ca2+ imaging. The entire SR could be depleted or refilled from one small site via either inositol 1,4,5-trisphosphate receptors (IP3R) or ryanodine receptors (RyR) suggesting the SR is luminally continuous and that Ca2+ may diffuse freely throughout. Notwithstanding, regulation of the opening of RyR and IP3R, by the [Ca2+] within the SR, may create several apparent SR elements with various receptor arrangements. IP3R and RyR may appear to exist entirely on a single store, and there may seem to be additional SR elements that express either only RyR or only IP3R. The various SR receptor arrangements and apparently separate Ca2+ storage elements exist in a single luminally continuous SR entity.

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