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Updated: Jul 9, 2026

Analysis of Tubular Membrane Networks in Cardiac Myocytes from Atria and Ventricles
Published on: October 15, 2014
A single luminally continuous sarcoplasmic reticulum with apparently separate Ca2+ stores in smooth muscle
John G McCarron1, Marnie L Olson
1Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, John Arbuthnott Building, 27 Taylor Street, Glasgow G4 0NR, Scotland, United Kingdom. john.mccarron@strath.ac.uk
The sarcoplasmic reticulum (SR) in smooth muscle cells is a single, continuous network. Calcium ions (Ca2+) can freely diffuse throughout this interconnected structure, regardless of receptor type.
Area of Science:
- Cellular Biology
- Muscle Physiology
- Calcium Signaling
Background:
- The structure of the sarcoplasmic reticulum (SR) in smooth muscle cells is debated.
- It is unclear whether the SR comprises a single, continuous lumen or multiple, separate calcium (Ca2+) pools.
Purpose of the Study:
- To investigate the structural organization of the SR in smooth muscle cells.
- To determine if the SR is a continuous network or composed of discrete Ca2+ stores.
Main Methods:
- Utilized voltage-clamped single smooth muscle cells.
- Employed local photolysis of caged compounds combined with Ca2+ imaging.
Main Results:
- The entire SR could be depleted or refilled from a single small site.
- This occurred via either inositol 1,4,5-trisphosphate receptors (IP3R) or ryanodine receptors (RyR).
- Evidence suggests Ca2+ diffuses freely throughout a luminally continuous SR.
Conclusions:
- The SR in smooth muscle cells is a single, luminally continuous entity.
- Apparent separate Ca2+ storage elements and varied receptor arrangements arise from localized regulation of IP3R and RyR by intraluminal Ca2+ concentrations.
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