Muscle contraction RyRs are activated by a calcium trigger, which is brought about by the flow of through the L-type calcium channels. Furthermore, cardiac muscle tend to exhibit diad (or dyad) structures, rather than triads. Excitation-contraction coupling in cardiac muscle cells occurs when an action potential is initiated by pacemaker cells in the sinoatrial node or Atrioventricular node and conducted to all cells in the heart via gap junctions. The action potential travels along the surface membrane into T-tubules (the latter are not seen in all cardiac cell types) and the depolarisation causes extracellular to enter the cell via L-type calcium channels
Milrinone of the cardiomyocytes therefore increasing the rate at which cells can depolarize and generate contraction. PKA also phosphorylates components on myofilaments allowing actin and myosin to interact more easily and thus increasing contractility and the inotropic state of the heart. Milrinone allows stimulation of cardiac function independently of β-adrenergic receptors which appear to be down-regulated in those with heart failure. In recent years many studies have been performed showing that milrinone use may present potential adverse side effects in heart failure patients. Milrinone Milrinone, commonly known and marketed under the brand name Primacor, is a medication used in patients who