Contractility of cardiac muscle depends on: (A) On T tubules, (B) On T tubules and extracellular Ca2+, (C) On extracellular Ca2+, (D) On intracellular Ca2+
Answer is B. Excitation and contraction coupling is there in cardiac muscle. When an action potential reaches the T tubules there is activation of Dihydropyridine channels. This causes influx of extracellular calcium into sarcoplasm. Ref: Textbook of medical physiology by N Geetha, 2nd edition, page no. 53