During an action potential in a ventricular cardiomyocyte, calcium-induced calcium release (CICR) from the sarcoplasmic reticulum is triggered by Ca²⁺ entry through which channel, and the SR release channel involved is:
- A T-type (Cav3.2) channel triggers; IP3 receptor 1 (IP3R1) releases SR Ca²⁺
- B L-type (Cav1.2) channel triggers; ryanodine receptor 2 (RyR2) releases SR Ca²⁺ ✓
- C Sodium-calcium exchanger (NCX) operating in reverse triggers; RyR2 releases SR Ca²⁺
- D L-type channel triggers; SERCA pump releases SR Ca²⁺ during depolarization
Correct answer: B. L-type (Cav1.2) channel triggers; ryanodine receptor 2 (RyR2) releases SR Ca²⁺
Explanation
The dihydropyridine-sensitive L-type Ca²⁺ channel (Cav1.2) opens during phase 2 of the ventricular action potential, allowing a small Ca²⁺ influx that acts as a trigger at dyadic junctions to open the ryanodine receptor 2 (RyR2) on the SR. This CICR amplifies the Ca²⁺ signal 10–20-fold. T-type channels are expressed in pacemakers, not ventricular myocytes. IP3R1 plays a minor modulatory role. SERCA pumps Ca²⁺ back into the SR during relaxation, not release.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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