Question

Smooth muscle cells lack T tubules. Instead, membrane specializations called caveolae are thought to be involved in Ca²⁺ in these cells. Caveolae are invaginations of the plasma membrane that contain Ca²⁺ pumps, Ca²⁺ channels, and hormone receptors. It is thought that caveolae may be responsible for the direct entry of Ca²⁺ from outside the cells via ion channels and its removal by pumping. They may also signal release and reuptake of Ca²⁺ from the smooth endoplasmic reticulum. True or False?

Answer 1

The statement is True, as smooth muscle cells utilize caveolae for calcium regulation, which are responsible for the direct entry of extracellular Ca++ and its removal. These caveolae are crucial for smooth muscle contraction.

Step-by-step explanation:

The statement is True. Smooth muscle cells indeed lack T tubules; instead, they have caveolae, which are small invaginations of the plasma membrane. These caveolae are essential for calcium regulation within the muscle cell, serving roles in both calcium entry into the cell from the extracellular space and facilitating the process of calcium removal. The influx of extracellular Ca++ through the caveolae contributes significantly to the calcium that initiates smooth muscle contraction. Calcium can also be released from the sarcoplasmic reticulum (SR) within the smooth muscle cell, further contributing to muscular contraction.