<prompt> True regarding excitation contraction coupling in smooth muscle isPresence of troponin is essentialSustained contraction occurs with high calcium concentrationPhosphorylation of actin is required for contractionPresence of cellular calcium is essential to cause muscle contraction  <response>: Ans. d Presence of cellular calcium is essential to cause muscle contractionRef: Ganong, 25th edp.116Troponin is absent in smooth muscleSustained contraction latch occurs with less use of ATPPhosphorylation of myosin is required for smooth muscle contraction 