Molecular Anatomy of the Heart (III)

Thin filament at the Z-disc.  This region of the sarcomere is a rather sophisticated structure which serves mechanical and regulatory functions.  It also allows for the organization of the thin filaments in a ratio of 6 thin filaments around one single thick filament.   Multiple proteins are present at the Z-disc.  T-Cap is a capping protein present at the end of the titin molecules.  Filamin is the capping protein at the end of the thin filament.  CARP extends away from the Z-disc and, along with nebulette and filamin, may form the visible N-disc seen on electron microscopy.  Other proteins which are present here include ALP, calcineurin, calsarcin, mink, myopadin, myopalladin, MLP, and ZASP/Cypher/LDB3.  Some of these proteins are thought to form part of the cardiac stretch-sensing mechanism which may, in turn, mediate signal transduction to adapt to hypertrophic stimuli.  The core of the organization of the Z-disc is α-actinin.  Many of the proteins identified in the Z-disc are thought to interact with α-actinin.  Mutations in several of these proteins have been described in patients with dilated and hypertrophic cardiomyopathies.
The Desmin filaments play a role in keeping the sarcomeres in register throughout the myocyte, and also anchor the sarcoplasmic cytoskeleton to the sarcolemmal cytoskeleton.