Autonomic Receptor Subtypes, Mechanisms, and Effects

Vocabulary flashcards covering the distribution, G-protein coupling mechanisms, signaling pathways, and physiological effects of autonomic adrenergic, muscarinic, and nicotinic receptors.

$$\alpha_1\text{-Adrenergic Receptor Distribution}$$

Blood vessels (arterioles and veins), iris radial muscle, prostate gland, urinary bladder neck, and liver.

$$\alpha_1\text{-Adrenergic Receptor Mechanism}$$

Couples to $G_q\text{-protein}$, activating phospholipase-C to increase $\text{IP}_3 \& \text{DAG}$ and intracellular $\text{Ca}^{2+}$, causing smooth muscle contraction and glycogenolysis.

$$\alpha_1\text{-Adrenergic Receptor Effects}$$

Vasoconstriction, increased blood pressure, mydriasis (pupil dilation), urinary retention, prostate contraction, and glycogenolysis.

$$\alpha_2\text{-Adrenergic Receptor Distribution}$$

Presynaptic neurons, postsynaptic tissues (ocular, adipose, intestinal, hepatic, renal endocrine), pancreas ($\beta\text{ cells}$), and arterioles.

$$\alpha_2\text{-Adrenergic Receptor Mechanism}$$

Couples to $G_i\text{-protein}$ to inhibit adenylate cyclase enzyme and decrease $\text{cAMP}$, decreasing intracellular $\text{Ca}^{2+}$ and inhibiting neurotransmitter release and cellular activity.

$$\alpha_2\text{-Adrenergic Receptor Effects}$$

Decreased norepinephrine, decreased sympathetic outflow, decreased insulin secretion, platelet aggregation, decreased aqueous humor production, sedation, and analgesia.

$$\beta_1\text{-Adrenergic Receptor Distribution}$$

Heart (SA and AV node) and juxtaglomerular cells of the kidney.

$$\beta_1\text{-Adrenergic Receptor Mechanism}$$

Couples to $G_s\text{-protein}$ to activate adenylate cyclase, increasing $\text{cAMP}$ to cause increased $\text{Ca}^{2+}$ entry into cardiac cells and stimulate renin release.

$$\beta_1\text{-Adrenergic Receptor Effects}$$

Increased heart rate, increased force of contraction, increased conduction velocity, increased cardiac output, and renin release.

$$\beta_2\text{-Adrenergic Receptor Distribution}$$

Bronchial smooth muscles, blood vessels of skeletal muscles, uterus, liver, GI smooth muscles, urinary bladder (detrusor muscle), and ciliary epithelium.

$$\beta_2\text{-Adrenergic Receptor Mechanism}$$

Couples to $G_s\text{-protein}$ to activate adenylate cyclase enzyme, increasing $\text{cAMP}$ to relax smooth muscles, promote glycogenolysis, gluconeogenesis, and increase insulin secretion.

$$\beta_2\text{-Adrenergic Receptor Effects}$$

Bronchodilation, vasodilation, uterine relaxation, bladder relaxation, glycogenolysis, gluconeogenesis, and increased insulin secretion.

$$\beta_3\text{-Adrenergic Receptor Distribution}$$

Adipose tissue and urinary bladder (detrusor muscle).

$$\beta_3\text{-Adrenergic Receptor Mechanism}$$

Couples to $G_s\text{-protein}$ to activate adenylate cyclase (AC) enzyme, increasing $\text{cAMP}$ to activate lipase and relax bladder smooth muscle.

$$\beta_3\text{-Adrenergic Receptor Effects}$$

Lipolysis, thermogenesis, relaxation of urinary bladder, and increased bladder capacity.

$$M_1\text{ Muscarinic Receptor Distribution}$$

Autonomic ganglia, gastric glands, and enteric neurons.

$$M_1\text{ Muscarinic Receptor Mechanism}$$

Couples to $G_q\text{-protein}$ to activate phospholipase-C (PLC) enzyme, increasing $\text{IP}_3 \& \text{DAG}$ and intracellular $\text{Ca}^{2+}$.

$$M_1\text{ Muscarinic Receptor Effects}$$

Gastric secretion, relaxation of lower esophageal sphincter (LES) pressure, intestinal secretion, and motor function.

$$M_2\text{ Muscarinic Receptor Distribution}$$

Cardiac smooth muscle.

$$M_2\text{ Muscarinic Receptor Mechanism}$$

Couples to $G_i\text{-protein}$ to inhibit adenylate cyclase enzyme, decreasing $\text{cAMP}$ and causing $K^+$ channel opening and hyperpolarization.

$$M_2\text{ Muscarinic Receptor Effects}$$

Decreased rate of impulse generation at the SA-node, decreased conduction velocity at the AV-node, decreased contractility in atrium and ventricle, decreased acetylcholine (Ach) release, analgesia, and tremor in the CNS.

$$M_3\text{ Muscarinic Receptor Distribution}$$

Visceral and bronchial smooth muscle, ciliary muscle, exocrine glands, and blood vessels / endothelium.

$$M_3\text{ Muscarinic Receptor Mechanism}$$

Couples to $G_q\text{-protein}$ to activate phospholipase-C enzyme, increasing $\text{IP}_3 \& \text{DAG}$ and intracellular $\text{Ca}^{2+}$ causing smooth muscle contraction.

$$M_3\text{ Muscarinic Receptor Effects}$$

Bronchial smooth muscle contraction, exocrine gland secretion, and vasodilation.

$$N_M\text{ Nicotinic Receptor Distribution}$$

Skeletal muscle end plate.

$$N_M\text{ Nicotinic Receptor Mechanism and Effects}$$

Opening of $\text{Na}^+$ and $\text{K}^+$ channels leads to depolarization of the skeletal muscle end plate, causing contraction of skeletal muscle.

$$N_N\text{ Nicotinic Receptor Distribution}$$

Autonomic ganglia, adrenal medulla, and certain areas of the brain.

$$N_N\text{ Nicotinic Receptor Mechanism and Effects}$$

Opening of $\text{Na}^+$, $\text{K}^+$, and $\text{Ca}^{2+}$ channels leads to depolarization, resulting in potent postganglionic impulse generation, increased catecholamine release, and excitation or inhibition in certain areas of the brain.