Calcium is released within cells through two primary mechanisms.
Sources of Calcium Release
The systolic calcium transient, a temporary increase in calcium concentration, arises from two distinct sources:
- Entry from Extracellular Fluid: Calcium ions enter the cell from the surrounding extracellular fluid.
- Release from Sarcoplasmic Reticulum (SR): Calcium is released from the sarcoplasmic reticulum, an internal calcium storage organelle within the cell.
Voltage-Activated L-Type Calcium Current
The major pathway for calcium entry from the extracellular fluid is through the voltage-activated L-type calcium current. This mechanism is triggered by changes in the cell's electrical potential.
Summary
| Source | Mechanism |
|---|---|
| Extracellular Fluid | Voltage-activated L-type calcium current |
| Sarcoplasmic Reticulum (SR) | Release from internal stores within the cell |
In essence, calcium release is a combination of calcium entering the cell from outside and being released from internal storage sites. The specific method of entry is predominantly through L-type calcium channels, while release also occurs from the sarcoplasmic reticulum.
