4/25/2013
Muscle contraction
The sliding filament model
12.03.2013.
Phase contrast microscopy
Frits (Frederik) Zernike
Born: 16 July 1888, Amsterdam, the
Netherlands
Died: 10 March 1966, Groningen, the
Netherlands
Affiliation at the time of the award:
Groningen University, Groningen, the
Netherlands
Nobel Prize motivation: "for his demonstration
of the phase contrast method, especially for
his invention of the phase contrast
microscope"
Field: Optical physics (1953)
Fritz Zernike (1942). "Phase contrast, a new method for the microscopic observation of transparent objects part I". Physica 9 (7): 686–698.
Fritz Zernike (1942). "Phase contrast, a new method for the microscopic observation of transparent objects part II". Physica 9 (10): 974–980.
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Sliding filament model I.
• HUXLEY AF, NIEDERGERKE R. Structural
changes in muscle during contraction;
interference microscopy of living muscle
fibres. Nature. 1954 May 22;173(4412):971-3.
Sir Andrew Huxley
• English physiologist and biophysicist
• born 22 November 1917, Hampstead, London
• won the 1963 Nobel Prize in Physiology
(with Sir Alan Lloyd Hodgkin on the basis of nerve
action potentials)
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Work that was done
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Worked with interference microscopy.
Used muscle fibres.
Measured the width of the A and I band.
Different conditions
– passive shortening (stretching)
– isotonic contraction (constant force)
– isometric twitches (constant size)
summary
• The ratio of widths of the A band and the I
band depends on the length of the fibre and
unaffected by tension development (force
production).
• The myosin in A bands is in the form of
submicroscopic rods with a definite length.
• During contraction the actin filaments are
drawn into the A bands, between the rodlets
of the myosin.
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Sliding filament model II.
HUXLEY H, HANSON J. Changes in the crossstriations of muscle during contraction and
stretch and their structural interpretation.
Nature. 1954 May 22;173(4412):973-6. PubMed
PMID: 13165698.
Hugh Huxley
• born on February 25, 1924
• British biologist
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Work that was done
• Worked with phase contrast microscopy.
• Used isolated myofibrils (blending glycerol extracted
rabbit psoas muscle) on a microscope slide under a
coverslip.
– small size -> less optical artifacts
– slow contraction when treated with ATP
• Followed the change of the A and I band.
• Different conditions
– contraction induced by ATP
– stretch
– myosin extraction after stretch and after contraction
Conclusions
• During contraction and stretch of the
myofilaments the I-bands are changing while the
A-bands remain unchanged.
• A possible driving force for contraction might be
the formation of actin-myosin linkages
(crossbridges) when ATP is split by the myosin.
• The actin filaments might be drawn into the array
of myosin filaments in order to present to them
as many active groups for acto-myosin formation
as possible.
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• The end!
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