**Core Concept**
Lubiprostone is a medication used to treat constipation, specifically idiopathic constipation and irritable bowel syndrome with constipation (IBS-C). It works by activating chloride channels in the intestinal epithelial cells, increasing the amount of water and chloride ions in the intestinal lumen, and promoting intestinal secretion.

**Why the Correct Answer is Right**
Lubiprostone acts on the CIC-2 chloride channel, which is expressed in the intestinal epithelial cells. This activation leads to an increase in chloride secretion, resulting in an increase in intestinal fluid and promoting bowel movements. The increased fluid secretion also helps to soften the stool, making it easier to pass.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because lubiprostone does not primarily work through the enteric nervous system (ENS), unlike drugs like linaclotide.
**Option B:** This option is incorrect because lubiprostone does not primarily work through the release of gastrin, unlike drugs like domperidone.
**Option C:** This option is incorrect because lubiprostone does not primarily work through the inhibition of serotonin reuptake, unlike drugs like fluoxetine.

**Clinical Pearl / High-Yield Fact**
Lubiprostone is a chloride channel activator that can be used as a first-line treatment for constipation, particularly in patients with IBS-C. It is also effective in patients with opioid-induced constipation.

**Correct Answer:** C. A chloride channel activator used to treat constipation.