Two Kinases to Soften the Heart

Abstract

The springlike protein titin is a key regulator of heart muscle mechanics. At the half-sarcomere (Fig. 1 A), the smallest functional unit of cardiac muscle, titin is responsible for producing a passive force when the heart is stretched during diastolic filling of the ventricles. The passive force, added to the active force produced by interactions between the thick and thin filaments, is responsible for the power output of the heart. Each single titin molecule spans the entire half-sarcomere, from the Z disk to the M band in the center of the thick filaments (3).