calcium ion transmembrane import into cytosol

Definition

Target type: biologicalprocess

A process in which a calcium ion is transported from one side of a membrane to the other into the cytosol by means of some agent such as a transporter or pore. [GOC:vw]

Calcium ion transmembrane import into the cytosol is a fundamental biological process that plays a crucial role in a wide range of cellular functions, including muscle contraction, nerve impulse transmission, and signal transduction. It involves the movement of calcium ions (Ca2+) from the extracellular environment or intracellular compartments, such as the endoplasmic reticulum (ER), across the plasma membrane or organellar membranes, respectively, into the cytosol.

The process of calcium ion transmembrane import is tightly regulated and involves a complex interplay of membrane proteins, ion gradients, and signaling pathways. Here's a detailed description:

1. **Calcium Channels:**
- **Voltage-gated calcium channels (VGCCs):** These channels are activated by changes in membrane potential, primarily found in excitable cells like neurons and muscle cells. They allow calcium influx into the cytosol upon depolarization.
- **Ligand-gated calcium channels:** These channels are activated by the binding of specific ligands, such as neurotransmitters or hormones. They are often involved in signal transduction pathways.
- **Store-operated calcium channels (SOCs):** These channels are activated by depletion of calcium stores within the ER. They allow calcium influx from the extracellular environment to replenish the ER stores.

2. **Calcium Pumps:**
- **Plasma membrane calcium ATPase (PMCA):** This pump actively transports calcium ions out of the cytosol and into the extracellular space, maintaining a low intracellular calcium concentration. It is driven by ATP hydrolysis.
- **Sarco/endoplasmic reticulum Ca2+-ATPase (SERCA):** This pump actively transports calcium ions from the cytosol into the ER lumen, sequestering calcium and maintaining a high concentration within the ER. It is also ATP-driven.

3. **Calcium Ion Gradients:**
- There is a steep concentration gradient of calcium ions across the plasma membrane, with a much higher concentration outside the cell than inside. This gradient is maintained by the activity of PMCA pumps.
- Similarly, there is a gradient between the cytosol and the ER lumen, with a higher concentration of calcium within the ER due to the activity of SERCA pumps.

4. **Calcium Binding Proteins:**
- **Calmodulin (CaM):** This protein binds to calcium ions and undergoes conformational changes, allowing it to interact with and regulate a wide range of target proteins, such as kinases, phosphatases, and ion channels.
- **Troponin C:** This protein binds to calcium ions in muscle cells and triggers muscle contraction.

5. **Signal Transduction:**
- Calcium ion influx into the cytosol acts as a second messenger, initiating signal transduction cascades.
- Calcium binding to CaM activates downstream signaling pathways, leading to various cellular responses, including gene expression, cell growth, and apoptosis.

6. **Regulation of Calcium Ion Import:**
- The process of calcium ion transmembrane import is tightly regulated by various mechanisms, including:
- Phosphorylation of calcium channels.
- Binding of specific regulatory proteins.
- Changes in membrane potential.
- Interaction with signaling pathways.

The precise mechanisms of calcium ion transmembrane import vary depending on the cell type, the specific calcium channels involved, and the physiological context. However, the overall process is essential for maintaining cellular homeostasis and regulating a wide range of cellular functions.'
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Proteins (6)

Compounds (73)