Contraction of ventricular myocytes depends on calcium-induced calcium release. During the plateau of the action potential, calcium entering through L-type channels triggers release of additional calcium from the sarcoplasmic reticulum through which channel?

• A Sodium-calcium exchanger (NCX)
• B Inositol trisphosphate receptor (IP3R)
• C SERCA pump on the sarcolemma
• D Ryanodine receptor type 2 (RyR2) ✓

Explanation

The small calcium influx through L-type channels during phase 2 activates ryanodine receptor type 2 clusters on the sarcoplasmic reticulum, releasing enough stored calcium to bind troponin C and initiate contraction. SERCA resequesters calcium into the SR during relaxation and is not a release channel, the NCX extrudes calcium across the sarcolemma, and IP3 receptors play a minor role in cardiac muscle compared with their dominant role in smooth muscle.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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