All of the following would generally depolarize intestinal smooth muscle EXCEPT: A. Distension B. Adrenergic Transmitters C. Cholinergic Agents D. Vagal Discharge E. Myenteric Plexus Activation
BAn inherent property of smooth-muscle cells is that a stretch causes depolarization and a contraction. Parasympathetic releasing ACh, and other cholinergic drugs, also depolarize and increase activity, much of this working through the myenteric plexus. On the other hand, adrenergic activity to the gut inhibits smooth muscle and decreases activity.
The correct answer is B. Adrenergic transmitters.
Adrenergic transmitters, such as norepinephrine, typically result in smooth muscle relaxation by activating beta receptors. This is because adrenergic receptors are coupled with G protein-coupled receptors, which activate intracellular signals that lead to muscle relaxation.
On the other hand, distension, cholinergic agents (such as acetylcholine), vagal discharge, and activation of the myenteric plexus all lead to depolarization of intestinal smooth muscle. This depolarization can trigger the opening of voltage-gated calcium channels and subsequent contraction of the smooth muscle cells.
Therefore, all options except B would depolarize intestinal smooth muscle.
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