**Core Concept:**
Facilitative glucose transporters (GLUTs) are a group of membrane proteins responsible for facilitating the passive transport of glucose across cell membranes. They play a crucial role in the uptake of glucose by various cell types, including myocytes (muscle cells). The correct answer refers to a specific member of the GLUT family that is expressed in muscle cells.

**Why the Correct Answer is Right:**
The correct answer, GLUT4, is a specific glucose transporter expressed in muscle cells (myocytes). GLUT4 is particularly important for glucose uptake during periods of high energy demand, such as during exercise or during insulin-stimulated situations. Its function is crucial for maintaining blood glucose levels and preventing hypoglycemia.

**Why Each Wrong Option is Incorrect:**
A. GLUT1 is primarily found in the brain and erythrocytes, not myocytes.
B. GLUT2 is mainly expressed in liver and kidney cells, not muscle cells.
C. GLUT3 is expressed in neurons and not relevant to myocytes.

**Clinical Pearl / High-Yield Fact:**
Understanding the role of GLUT4 in glucose uptake by myocytes is essential for understanding glucose homeostasis and the pathophysiology of diabetes, particularly in conditions like insulin resistance and type 2 diabetes, where glucose uptake in muscle cells is impaired. This can lead to decreased insulin sensitivity and increased risk of hyperglycemia and other complications.

**Correct Answer:** .GLUT4.