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EGTA chelates Ca₂⁺ with high affinity and specificity. Which of the following processes would be inhibited by microinjection of EGTA into the target cell?

1) I Glucagon-triggered breakdown of glycogen in liver by activation of adenylyl cyclase
2) II Vasopressin-triggered breakdown of glycogen in liver by activation of phospholipase C-β
3) III Acetylcholine-triggered contraction in smooth muscle by activation of phospholipase C-β

1 Answer

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Final answer:

Microinjection of EGTA would inhibit the vasopressin-triggered glycogen breakdown and acetylcholine-triggered smooth muscle contraction, as they depend on calcium signaling activated by phospholipase C-β; glucagon-triggered glycogen breakdown remains unaffected.Option II & III are the answers.

Step-by-step explanation:

EGTA is a chelating agent that binds Ca²⁺ ions with high specificity, which would disrupt signaling pathways dependent on calcium. Among the processes listed, vasopressin-triggered breakdown of glycogen in the liver and acetylcholine-triggered contraction in smooth muscle, both depend on phospholipase C-β activation, which requires Ca²⁺ ions as a cofactor. The breakdown of glycogen initiated by glucagon does not involve a pathway requiring Ca²⁺ ions, instead relying on adenylyl cyclase. Therefore, microinjection of EGTA into a cell would inhibit processes II and III, as they are depending on pathways that involve calcium signaling, whereas process I would likely remain unaffected.

EGTA, a selective chelating agent, holds high specificity for binding Ca²⁺ ions. In processes II and III, vasopressin-triggered glycogen breakdown and acetylcholine-induced smooth muscle contraction, the activation of phospholipase C-β crucially relies on calcium as a cofactor. EGTA's binding of Ca²⁺ disrupts these calcium-dependent signaling pathways, inhibiting both processes. Conversely, process I, involving glucagon-triggered glycogen breakdown, operates through an adenylyl cyclase-dependent pathway unaffected by EGTA. Thus, microinjection of EGTA into a cell would selectively impede calcium-dependent processes II and III, illustrating its precision in modulating specific cellular signaling cascades.

User Alex Hartford
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