**Core Concept**
The myogenic hypothesis of renal autoregulation proposes that the afferent arterioles constrict in response to an increase in blood pressure, thereby maintaining a relatively constant glomerular filtration rate (GFR) across a wide range of blood pressures. This mechanism is crucial for maintaining renal function and electrolyte balance.

**Why the Correct Answer is Right**
The afferent arterioles are sensitive to stretch, which activates mechanoreceptors that initiate a signaling cascade leading to the opening of calcium (Ca2+) channels. The influx of Ca2+ ions into the smooth muscle cells of the afferent arterioles triggers muscle contraction, resulting in vasoconstriction. This response helps to reduce blood flow to the glomerulus, thereby maintaining a constant GFR despite changes in blood pressure. The opening of Ca2+ channels is a key step in the myogenic response, allowing the afferent arterioles to adjust their diameter in response to changes in blood pressure.

**Why Each Wrong Option is Incorrect**
**Option A:** NO (nitric oxide) release typically causes vasodilation, which would increase blood flow to the glomerulus, rather than constricting the afferent arterioles.
**Option B:** Noradrenaline release can cause vasoconstriction, but it is not the primary mechanism underlying the myogenic response in afferent arterioles.
**Option D:** Adenosine release can cause vasodilation and is involved in other regulatory mechanisms, but it is not directly related to the myogenic response in afferent arterioles.

**Clinical Pearl / High-Yield Fact**
The myogenic response is a key mechanism for maintaining renal autoregulation, but it can be disrupted in diseases such as hypertension, where the afferent arterioles may become less responsive to stretch, leading to increased GFR and potential kidney damage.

**✓ Correct Answer: C. Opening of Ca2+ channels**