Mice Lacking RyR2 Learn The Down Side Of Being Big Hearted

However, the molecular reasons why these mutations are associated with impaired heart function have not been determined and many questions remain about how this protein is regulated. For example, in vitro studies have shown that a protein known as calmodulin (CaM) inhibits RyR2 function, but the physiological significance of this was not known.

In a study that appears online on April 12, in advance of publication in the May print issue of the Journal of Clinical Investigation, Gerhard Meissner and colleagues from the University of North Carolina at Chapel Hill, found that mice expressing only a mutant form of RyR2 that cannot bind CaM showed signs of cardiac hypertrophy (thickening of the walls of the heart) as early as 1 day after birth and died within 16 days of birth.

Further analysis indicated that cardiac muscle cells from these mice showed abnormal release of calcium from a cellular compartment known as the sarcoplasmic reticulum and that the heartbeat of these mice was substantially slower than the heartbeat of normal mice. This study indicates that CaM inhibition of RyR2 is crucial for normal cardiac function in mice, but it will be important to determine whether impaired CaM inhibition of RyR2 is associated with the human heart diseases linked to mutations in the gene that makes RyR2.