Automaticity (chronotropy): the ability to initiate an electrical impulse. Conductivity (dromotropy): the ability to conduct an electrical impulse. Contractility (inotropy): the ability to contract. Lusitropy: the ability to relax and to fill.
Cardiac muscle cells form a structural and functional syncytium (a complex three-dimensional network), being linked by low-resistance intercalated disks. The cells measure 16-100 mm in length and 12-20 mm in diameter.
The intercalated discs serve the following functions: The connection of adjacent cells via desmosomes. The connection of actin filaments of adjacent cells.
Tight intercellular coupling through low-resistance gap junctions. Each gap junction consists of a cluster of several ion channels. Each channel comprises two hemi-channels or connexons. Each connexon is made up of six connexin molecules that traverse the lipid bilayer and form a central pore. Isoform-specific determinants of conductance, selectivity and gating are located in the cytoplasmic domains of the connexins.
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