Identifying the calcium-regulated step in the actomyosin ATPase reaction in muscle
| Project/Area Number |
08640873
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
動物生理・代謝
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| Research Institution | Teikyo University |
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Principal Investigator |
IWAMOTO Hiroyuki Teikyo University, School of Medicine, Lecturer, 医学部, 講師 (60176568)
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| Project Period (FY) |
1996 – 1997
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| Project Status |
Completed (Fiscal Year 1997)
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| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1997: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1996: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Keywords | muscle / calcium / actomyosin / ATPase reaction / kinetics / inorganic phosphate / skeletal muscle / force generation |
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| Research Abstract |
Contraction of skeletal muscle is regulated by intracellular calcium levels [Ca^<2+>]. The [Ca^<2+>] -regulated step in the actomyosin ATPase reaction has remained to be identified. We performed experiments to specify the step (s) which is regulated by [Ca^<2+>].
We used skinned skeletal muscle fibers from rabbit, and added inorganic phosphate (Pi) to the bathing solution to increase the relative population of the low force A・M・ADP・P_i intermediate. The relative population of this intermediate was unchanged by lowering [Ca^<2+>], indicating that it is the step of formation of the low force intermediate that is regulated by [Ca^<2+>]. We further showed that the rate of dissociation of this low force actomyosin complex is not affected by [Ca^<2+>]. Therefore the forward rate constant for the formation of the A・M・ADP・P_i intermediate should be regulated by [Ca^<2+>].
Next we studied in more detail the way in which the formation of the A・M・ADP・P_i intermediate is regulated. The questions addressed were : (1) Is [Ca^<2+>] the only factor that regulates the formation of the A・M・ADP・P_i intermediate? (2) How can the [Ca^<2+>] dependence of shortening velocity by reconciled with the present conclusion that it is A・M・ADP・P_i, not the later intermediates which are more relevant to shortening, that is the primary target of [Ca^<2+>] regulation. To answer these questions, we measured the shortening velocity of muscle fibers by using a multiple shortening protocol. At saturating [Ca^<2+>] a fast shortening pattern was repeated many times. At submaximal [Ca^<2+>], the shortening velocity was decreased, and the velocity depended on the tension levle, i.e., the number of attached myosin heads, immediately before shortening. The results indicate that the formation of A・M・ADP・P_i is regulated not only by [Ca^<2+>], but also by the number of attached myosin heads. The [Ca^<2+>] dependence of shortening velocity is naturally understood as a consequence of this dual regulation mechanism.
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Report
(3 results)
Research Products
(3 results)
