What effect do beta-agonists have on intracellular calcium concentrations?

What effect do beta-agonists have on intracellular calcium concentrations?

• A. Increase concentrations
• B. Decrease concentrations
• C. No effect on concentrations
• D. Stabilize concentrations

Answer: (B)

Beta-agonists function primarily by activating beta-adrenergic receptors, which are G protein-coupled receptors that, when stimulated, primarily influence intracellular signaling pathways linked to adenylate cyclase activity. The activation of these receptors leads to an increase in cyclic AMP (cAMP) levels within the cell. The increase in cAMP has several downstream effects, particularly in smooth muscle and cardiac tissues. In smooth muscle, such as that found in the uterus or bronchi, the rise in cAMP levels causes a reduction in intracellular calcium concentrations. This mechanism is crucial for promoting muscle relaxation, which is why beta-agonists are often used as bronchodilators in respiratory conditions and can also affect uterine tone. By decreasing intracellular calcium concentrations, beta-agonists effectively inhibit contraction in smooth muscles, providing a therapeutic effect in conditions where relaxation of muscle is desirable, such as in the prevention of preterm labor. Thus, the correct choice is that beta-agonists decrease intracellular calcium concentrations.

Beta-agonists function primarily by activating beta-adrenergic receptors, which are G protein-coupled receptors that, when stimulated, primarily influence intracellular signaling pathways linked to adenylate cyclase activity. The activation of these receptors leads to an increase in cyclic AMP (cAMP) levels within the cell.

The increase in cAMP has several downstream effects, particularly in smooth muscle and cardiac tissues. In smooth muscle, such as that found in the uterus or bronchi, the rise in cAMP levels causes a reduction in intracellular calcium concentrations. This mechanism is crucial for promoting muscle relaxation, which is why beta-agonists are often used as bronchodilators in respiratory conditions and can also affect uterine tone.

By decreasing intracellular calcium concentrations, beta-agonists effectively inhibit contraction in smooth muscles, providing a therapeutic effect in conditions where relaxation of muscle is desirable, such as in the prevention of preterm labor.

Thus, the correct choice is that beta-agonists decrease intracellular calcium concentrations.