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Updated: Jul 16, 2026
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Measurement of Calcium Fluctuations Within the Sarcoplasmic Reticulum of Cultured Smooth Muscle Cells Using FRET-based Confocal Imaging
Published on: June 20, 2016
Sarcoplasmic reticulum calcium pump: a model for Ca2+ binding and Ca2+-coupled phosphorylation.
C Tanford1, J A Reynolds, E A Johnson
1Department of Physiology, Duke University Medical Center, Durham, NC 27710.
Summary
This study modifies the Ca2+ transport model for the sarcoplasmic reticulum Ca2+ pump, detailing a three-substate uptake mechanism. The revised model explains Ca2+ binding cooperativity and links Ca2+ binding to pump phosphorylation.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Physiology
Background:
- The sarcoplasmic reticulum Ca2+ pump facilitates calcium ion transport, crucial for muscle contraction.
- Existing models describe alternating access mechanisms for Ca2+ transport.
- The MacLennan-Green domain structure provides new insights into Ca2+-pump protein conformation.
Purpose of the Study:
- To modify the conventional alternating access model for Ca2+ transport.
- To incorporate the MacLennan-Green domain structure into a new model.
- To elucidate the mechanism of Ca2+ binding and its coupling to ATP utilization.
Main Methods:
- Development of a modified alternating access model for Ca2+ transport.
- Division of the E1 uptake state into three substates based on Ca2+-binding domain conformation.
- Integration of jaw-closing and hinge-bending steps to describe ion occlusion.
Main Results:
- The modified model proposes three substates for the E1 state, involving sequential Ca2+ binding and cavity closure.
- A constant transport stoichiometry of two Ca2+ ions per pump cycle is predicted.
- Ca2+ binding is identified as a mandatory prerequisite for pump phosphorylation, while ATP binding is independent.
Conclusions:
- The revised model provides a detailed mechanism for Ca2+ uptake and translocation.
- It explains the observed high cooperativity in Ca2+ equilibrium binding.
- The model offers a plausible explanation for the coupling between Ca2+ binding and ATP hydrolysis by the pump.
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