Membrane permeability is controlled by

Options

A. `Na^(+)`
B. `K^(+)`
C. Both A and B
D. `Ca^(2+)`

Answer

### Step-by-Step Solution:

1. **Understanding Membrane Permeability**:
- Membrane permeability refers to the ability of a cell membrane to allow substances to pass through it. This can include ions, molecules, and other substances.

2. **Role of Calcium Channels**:
- Calcium channels are specific proteins embedded in the cell membrane that facilitate the movement of calcium ions (Ca²⁺) across the membrane. These channels are crucial for maintaining the balance of ions inside and outside the cell.

3. **Intracellular and Extracellular Ion Concentrations**:
- Inside the cell, potassium ions (K⁺) are typically in higher concentration, while sodium ions (Na⁺) are more concentrated outside the cell. The movement of these ions across the membrane is essential for various cellular functions.

4. **Effect of Sodium Ion Concentration**:
- If the concentration of sodium ions increases inside the cell, it can trigger the sodium channels to open, allowing sodium ions to flow out of the cell. This movement is crucial for maintaining the electrochemical gradient across the membrane.

5. **ATP Dependency of Calcium Channels**:
- Calcium channels are ATP-dependent, meaning they require energy (in the form of ATP) to function properly. This energy is necessary for the active transport of calcium ions, which helps regulate membrane permeability.

6. **Conclusion**:
- Therefore, the control of membrane permeability is significantly influenced by calcium channels, which manage the flow of calcium ions and help maintain the overall ionic balance within the cell.

### Final Answer:
Membrane permeability is controlled by calcium channels.