Physiology Which of the following is TRUE regarding excitation contraction coupling mechanism in smooth muscles? A Presence of troponin is essential B Sustained contraction occurs with high calcium concentration C Phosphorylation of actin is required for contraction D Presence of cellular calcium is essential to cause muscle contraction 💡 Explanation Which of the following is TRUE regarding excitation contraction coupling mechanism in smooth muscles? ✓ Correct Answer: D. Presence of cellular calcium is essential to cause muscle contraction