Muscle fiber, the basic structure of muscle, is made of myofibrils and myofibril is made of contractile proteins that constitute myofilaments of myosin, actin, tropomyosin, troponin T, I, C.
Muscle contraction is done by interaction of myosin and actin. When Ca2+ ion is combined to troponin, C, the site of troponin I is changed and active site of actin is exposed. When myosin head is combined to this site, ATP ase in it breaks down
ATP
and
the energy produced by this way is used in muscle contraction.
So, ATP and Ca2+ ion are essential for muscle contraction.
By the way, ATPP, having one more phosphate than ATP, is somewhat similar to or even more potent then ATP for the effect on smooth muscle contraction in the extracellular circumstrances. But the action and the effect on ATPase of intracellular
ATPP
is
nor clear till now.
The purpose of this study was to find whether ATPP can be utilized as energy source in contraction of muscle fibers. The contraction by ATPP was compared with that by ATP in glycerinated muscle fibers.
@ES The results were as follows:
@EN 1. In the presence of 5mM ATP, the higher concentration of Ca2+ resulted in the more degree of shortening of glycerinated muscle fibers.
2. In the presence of 1mM ATP, the degree of shortening of glycerinated muscle fibers was increased as the higher concentration of Ca2+, but it was significantly lesser than by adding 5mM ATP(P<0.01, P<0.05).
3. In the solution with pCa 6, the degree of shortening was significantly greater when adding both 1mM ATP an 4mM ATPP than 1mM ATP only (P<0.001), and the degree was similar to that by adding 5mM ATP. However the degree of shortening by adding
5mm
ATPP was significantly lesser than 5mM ATP(P<0.001).
4. In the presence of single 5mM ATPP, the degree of shortening of muscle fibers was lesser than in the presence of 5mM ATP. Especially in solution with Ca2+ concentration more than pCa 6, the degree was significantly reduced (P<0.001).
5, In solution with pCa 6, by adding 1mM ATP and 4mm FDP, the degree of shortening was similar to that by adding 1mm ATP and degree was significantly lesser than by adding 5mM ATP(P<0.05).
These results suggest that ATPP can be utilized as an energy source in contraction as well as ATP.
The mechanism of the ATPP effects, however, seems to involve some synergy effect with ATP rather than the action of ATPP itself.
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