Related Experiment Video
Updated: Aug 3, 2026
10:05
Measurement of Calcium Fluctuations Within the Sarcoplasmic Reticulum of Cultured Smooth Muscle Cells Using FRET-based Confocal Imaging
Published on: June 20, 2016
Coordination between Ca2+ release and subsequent re-uptake in the sarcoplasmic reticulum
Biochemistry
|March 13, 1999
Summary
This study demonstrates that sarcoplasmic reticulum (SR) calcium release and re-uptake are coordinated, especially under intermediate calcium loading conditions. Optimized calcium loading in the SR reveals a biphasic transient, crucial for understanding muscle contraction regulation.
Area of Science:
- Biochemistry
- Cellular Physiology
- Muscle Contraction
Background:
- The sarcoplasmic reticulum (SR) plays a critical role in regulating intracellular calcium (Ca2+) levels, essential for muscle function.
- Understanding the kinetic relationship between Ca2+ release and re-uptake by the SR is vital for elucidating muscle excitation-contraction coupling.
- Previous studies often reported monophasic Ca2+ release, lacking detailed insights into the re-uptake phase.
Purpose of the Study:
- To produce and characterize a biphasic Ca2+ release and re-uptake transient in isolated sarcoplasmic reticulum (SR).
- To resolve the kinetic relationship between Ca2+ release and subsequent re-uptake of Ca2+.
- To investigate the coordination mechanisms between Ca2+ release channels (ryanodine receptors) and Ca2+ pumps.
Main Methods:
- Isolated sarcoplasmic reticulum (SR) was used to study Ca2+ dynamics.
- Polylysine, a ryanodine receptor-specific trigger, was employed to induce Ca2+ release at varying calcium loading levels and trigger concentrations.
- Stopped-flow spectroscopy with fluorescent Ca2+ indicators (fluo-3 and mag-fura-2AM) was utilized to measure Ca2+ concentrations in the reaction solution and SR lumen.
Main Results:
- Intermediate SR calcium loading (100-150 nmol/mg) induced biphasic Ca2+ transients, including both release and re-uptake phases, unlike higher loading levels.
- Increased polylysine concentration enhanced both the rate of Ca2+ release and re-uptake, indicating a coordinated response.
- A tight correlation was observed between Ca2+ release and re-uptake rates, suggesting re-uptake acceleration is controlled by the rate of lumenal Ca2+ decrease.
Conclusions:
- The study successfully generated biphasic Ca2+ transients in isolated SR, revealing a coordinated interplay between Ca2+ release and re-uptake.
- Calcium concentration gradients across the SR membrane are proposed as a key mechanism coordinating the biphasic Ca2+ transient.
- These findings provide critical insights into the fine-tuning of calcium dynamics essential for muscle physiology.
Related Concept Videos
01:26Cross-bridge Cycle
As muscle contracts, the overlap between the thin and thick filaments increases, decreasing the length of the sarcomere—the contractile unit of the muscle—using energy in the form of ATP. At the molecular level, this is a cyclic, multistep process that involves binding and hydrolysis of ATP, and movement of actin by myosin.
01:27Feedback Regulation of Calcium Concentration
Calcium is an essential signaling molecule required for various cellular functions. Calcium pumps and ion channels on cell and organellar membranes, such as those on the endoplasmic reticulum (ER), regulate calcium concentrations inside the cell. They remain closed, keeping the cytosolic calcium levels low at a resting state.
Various transmembrane receptors, such as G protein-coupled receptors (GPCRs), elicit a response to extracellular signals by increasing cytosolic calcium. Activated GPCRs...
Various transmembrane receptors, such as G protein-coupled receptors (GPCRs), elicit a response to extracellular signals by increasing cytosolic calcium. Activated GPCRs...
01:16Calmodulin-dependent Signaling
Calmodulin (CaM) is a calcium-binding protein in eukaryotes that controls various calcium-regulated cellular processes. It has four calcium-binding sites that bind calcium to form the calcium-calmodulin ( Ca2+-CaM) complex. GPCR stimulation increases the calcium levels in the cells that bind to CaM and induces a conformational change.
The Ca2+-CaM complex does not have enzymatic activity by itself. Instead, the complex binds downstream target proteins, including membrane proteins or enzymes,...
The Ca2+-CaM complex does not have enzymatic activity by itself. Instead, the complex binds downstream target proteins, including membrane proteins or enzymes,...
01:20Excitation-Contraction Coupling in Skeletal Muscles
Excitation-contraction coupling is a series of events that occur between generating an action potential and initiating a muscle contraction. It occurs at the triad, a structure found in skeletal muscle fibers that comprise a T-tubule and terminal cisternae of the sarcoplasmic reticulum on each side. These triads are visible in longitudinally sectioned muscle fibers. They are typically located at the A-I junction — the junction between the A and I bands of the sarcomere.
When an action potential...
When an action potential...
01:29Relaxation of Skeletal Muscles
The period of muscle contraction primarily influences the duration of stimulation at the neuromuscular junction (NMJ), the presence of free calcium ions in the sarcoplasm, and the availability of energy or ATP to support contractions.
When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated sodium channels. Sodium ions enter the cell, further depolarizing the presynaptic membrane. This depolarization causes voltage-gated calcium channels to open.
When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated sodium channels. Sodium ions enter the cell, further depolarizing the presynaptic membrane. This depolarization causes voltage-gated calcium channels to open.
01:25Smooth Muscle Contraction
Smooth muscle contraction is a complex process vital for various bodily functions, from maintaining blood vessel tension to facilitating the movement of food through the digestive tract. Unlike striated muscles, smooth muscle contraction begins more slowly and lasts longer.
The onset of contraction is triggered by an increase in calcium ions within the sarcoplasm, similar to the process in striated muscle. However, smooth muscles have a relatively smaller reservoir of the sarcoplasmic...
The onset of contraction is triggered by an increase in calcium ions within the sarcoplasm, similar to the process in striated muscle. However, smooth muscles have a relatively smaller reservoir of the sarcoplasmic...