**Core Concept**
The oxytocin receptor is a G protein-coupled receptor that plays a crucial role in the uterine contraction and milk letdown during lactation. It is a member of the rhodopsin-like GPCR family.

**Why the Correct Answer is Right**
The oxytocin receptor is coupled to Gq protein, which activates phospholipase C (PLC) to produce inositol trisphosphate (IP3) and diacylglycerol (DAG). IP3 triggers the release of calcium ions from the sarcoplasmic reticulum, leading to uterine contraction and milk letdown. The oxytocin receptor is specifically expressed in the myometrium and the mammary gland, where it mediates the effects of oxytocin.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not correctly describe the oxytocin receptor.
* **Option B:** This option is incorrect because it refers to a different type of receptor.
* **Option D:** This option is incorrect because it is not a known characteristic of the oxytocin receptor.

**Clinical Pearl / High-Yield Fact**
The oxytocin receptor is a key target for oxytocin, which is used clinically to induce labor and stimulate milk letdown during lactation.

**Correct Answer:** C. G protein-coupled receptor.