the molecular basis for myocardial contraction Flashcards
what are the main components of the myocardium
- contractile tissue
- connective tissue
- fibrous frame
- specialised conduction system
what does the cardiac myocyte do
1) pumping action of heart depends on interactions between contractile proteins in its muscular walls
2) the interactions transform chemical energy from ATP into mechanical work that movies blood under pressure from great veins into pulmonary artery and from the pulmonary veins into the aorta
3) the contractile proteins are activated by a signalling process called excitation - contraction coupling
4) this begins when action potential depolarises the cell and it ends when ionised calcium Ca2+ that appears within the cytosol binds to the Ca2+ receptor of the contractile apparatus
5) movement of Ca2+ into the cytosol is a passive process mediated by Ca2+ channels
6) the heart relaxes when ion exchangers and pumps transport Ca2+ uphill, out of the cytosol
structure of working myocardial cell
regular arrangement of cross striated myofibrils
these are actin and myosin
they are contractile proteins - they mediate sliding of contractile fibres (contraction) of a cell’s cytoskeleton, and of cardiac and skeletal muscle
function of the working myocardial cell do
cells that expand and contract in response to electrical impulses from the nervous system. These cardiac cells work together to produce the rhythmic, wave-like contractions that is the heartbeat
what does the plasma membrane of myocardial cell do
- regulates excitation-contraction coupling and relaxation
- separates the cytosol from extra cellular space and sarcoplasmic reticulum
where are myocardial cells found
cardiac muscle/myocardium
structure of myosin
- forms majority of THICK filament
- 2 large polypeptide heavy chains
- 4 light smaller light chains
- the polypeptides combine to form a molecule that consists of two globular heads (containing heavy and light chains) and a long tail formed by the two intertwined heavy chains.
what does myosin tail do during contraction
-the tail of each myosin molecule lies along the axis of the thick filament
and the two globular heads extend out to the sides forming cross-
bridges, which make contact with the thin filament and exert force
during muscle contraction.
structure of myosin globular head
- each globular head contains two binding sites, one for attaching to the thin filament and one for ATP.
-attached to the myosin head is an inorganic phosphate molecule (Pi) and ADP. - the ATP binding site also serves as an enzyme - an ATPase that hydrolyses the
bound ATP, harnessing its energy for contraction
structure of actin
- forms majority of THIN filament
- globular protein
- composed of single polypeptide that
polymerises with other actin monomers to form a polymer made up of two
INTERTWINED, helical chains. - these chains make up the core of the thin filament.
- each actin molecule contains a binding site for myosin
what is thin filament composed of
mainly actin
some troponin & tropomyosin
structure of tropomyosin
- elongated molecule
- 2 helical peptide chains
- occupies each of the longitudinal grooves between the two actin strands,
- overlies MYOSIN binding sites on actin
what does troponin do
- protein that changes shape when Ca2+ binds to it, when it does it
changes shape in doing so pushes the tropomyosin - EXPOSING myosin binding
sites on actin enabling contraction to occur
what is main source of energy for cardiac muscle
fatty acids
myocardial metabolism relies on free fatty acids during aerobic metabolism for efficient energy production
describe metabolism in hypoxia
hypoxia is low levels of oxygen in body tissues
during hypoxia there is no FFA (free fatty acids) metabolism,
so anaerobic metabolism occurs
