Question

While studying the activity of smooth muscle in blood vessels, Shelly discovers that, when applied to a muscle plasma membrane, a molecule chemically similar to a neurotransmitter triggers an increase in intracellular calcium ions. Which neurotransmitter is the molecule mimicking, and to which receptors is it binding?

Accepted Answer

Step 1: Identify the neurotransmitter involved in smooth muscle contraction in blood vessels. In vascular smooth muscle, the primary neurotransmitter that increases intracellular calcium ions is acetylcholine (ACh) or norepinephrine, but acetylcholine is well-known for acting through receptors that increase intracellular calcium. Step 2: Understand the receptor types on smooth muscle plasma membranes that respond to neurotransmitters. Acetylcholine binds to muscarinic receptors (a type of G protein-coupled receptor) on smooth muscle cells, which leads to an increase in intracellular calcium. Step 3: Recall the signaling pathway triggered by muscarinic receptor activation. When acetylcholine binds to muscarinic receptors, it activates phospholipase C via G proteins, which then produces inositol triphosphate (IP3). IP3 causes calcium release from the sarcoplasmic reticulum, increasing intracellular calcium concentration. Step 4: Conclude that the molecule mimicking the neurotransmitter is acting like acetylcholine, binding specifically to muscarinic receptors on the smooth muscle plasma membrane. Step 5: Summarize that the increase in intracellular calcium ions is due to activation of muscarinic receptors by an acetylcholine-like molecule, which triggers calcium release and smooth muscle contraction.

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Key Concepts

Neurotransmitters in Smooth Muscle Regulation

Receptors Mediating Calcium Influx in Smooth Muscle

Role of Intracellular Calcium in Smooth Muscle Contraction