CALCIUM-ACTIVATED TENSION OF SKINNED MUSCLE-FIBERS OF FROG - DEPENDENCE ON MAGNESIUM ADENOSINE-TRIPHOSPHATE CONCENTRATION
CALCIUM-ACTIVATED TENSION OF SKINNED MUSCLE-FIBERS OF FROG - DEPENDENCE ON MAGNESIUM ADENOSINE-TRIPHOSPHATE CONCENTRATION
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DOI：
10.1085/jgp.63.6.722
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发表时间：
1974-01-01
影响因子：
3.8
通讯作者：
GODT, RE
中科院分区：
文献类型：
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作者：
GODT, RE
在含有以下物质的溶液中检测MgATP对去皮青蛙肌纤维的Ca++激活的等长张力的影响：Mg++= 5 mM，磷酸肌酸（CP）= 14.5 mM，肌酸磷酸激酶（CPK）= 1 mg/ml，总EGTA= 7 mM，CaCl 2，KCl，咪唑> 20 mM，因此离子强度= 0.15，pH= 7.00，MgATP= 2 mM，0.1 mM，或20个原子能CP和CPK对于这些实验是必需的，这是通过它们对张力-Ca ++关系的影响实验确定的，对于CP> 14.5 mM，张力-Ca ++关系是饱和的。这被解释为意味着存在足够的CP以有效地缓冲胞内MgATP。降低MgATP使张力-pCa曲线向更高的pCa（-log Ca++）移动，因此，对于半最大张力：MgATP= 2 mM时pCal/2= 4.5，MgATP= 0.1 mM时pCal/2= 5.1，MgATP= 20 M# M时pCal/2= 5.8;然而，最大等长张力在所有情况下均相同。如果MgATP降低至1 M，则Ca++> 10-8 M时的张力为2 mM MgATP中最大Ca++激活张力的84%，并且仅略微增加至pCa= 4.5时的90%。Weber（1970，In The Physiology and Biochemistry of Muscle as Food，第2卷，EJ Mackey，RG Cassens，and BB Marsh，威斯康星州大学出版社，麦迪逊，威斯康星州），使用类似的溶液，观察到兔肌原纤维ATP酶速率的半最大钙激活的类似变化。在解释中，Weber和Bremel（1971，在肌肉细胞的收缩性和相关过程中，R. J. Podolsky，Prentice-Hall，Inc.编辑，Englewood Cliffs，NJ; Bremel and Weber，1972，iVat.新生物学，二百三十八：97）已经描述了一种机制，由此，在低ATP时，在肌球蛋白和细丝肌动蛋白之间形成”僵硬复合物”，并且继而改变肌钙蛋白上的两个Ca++结合位点中的一类的钙亲和力，使得细丝在较低Ca++水平下”开启”收缩。从结皮纤维的张力数据基本上支持这一假设。在FN Briggs的帮助下，在与用于结皮纤维的溶液类似的溶液中测定CaEGTA的稳定常数为2.62 × 101 M-1，并且对于100和300 mM KCl是相同的。
The influence of MgATP on the Ca++-activated isometric tension of skinned frog muscle fibers was examined in solutions containing: Mg++= 5 mM, creatine phosphate (CP)= 14.5 mM, creatinephosphokinase (CPK)= 1 mg/ml, total EGTA= 7 mM, CaC12, KC1, imidazole> 20 mM so that ionic strength= 0.15, pH= 7.00, and MgATP= 2 mM, 0.1 mM, or 20 AtM. CP and CPK were necessary for these experiments as determined experimentally by their effect on the tension-Ca++ relation, which was saturated for CP> 14.5 mM. This was interpreted to mean that sufficient CP was present to effectively buffer MgATP intracellularly. Decreasing MgATP shifts the tension-pCa curve to higher pCa (-log Ca++) so that, for half-maximal tension: pCal/2= 4.5 for MgATP= 2 mM, pCal/2= 5.1 for MgATP= 0.1 mM, and pCal/2= 5.8 for MgATP= 20 M# M; maximum isometric tension is the same in all cases, however. If MgATP was decreased to 1 M, tension at Ca++> 10-8 M was 84% of the maximum Ca++-activated tension in 2 mM MgATP and increased only slightly to 90% for pCa= 4.5. Weber (1970, In The Physiology and Biochemistry of Muscle as Food, Volume 2, EJ Briskey, RG Cassens, and BB Marsh, University of Wisconsin Press, Madison, Wis.), using similar solutions, observed similar shifts in half-maximal calcium activation of rabbit myofibril ATPase rates. In explanation, Weber and Bremel (1971, In Contractility of Muscle Cells and Related Processes, R.. J. Podolsky, editor, Prentice-Hall, Inc., Englewood Cliffs, NJ; Bremel and Weber, 1972, iVat. New Biol., 238: 97) have described a mechanism whereby, at low ATP," rigor complexes" are formed between myosin and thin filament actin and, in turn, alter the calcium affinity of one class of the two Ca++-binding sites on troponin, so that the thin filament is" turned on" for contraction at lower Ca++ levels. Tension data from skinned fibers substantially supports this hypothesis. A stability constant for CaEGTA of 2.62 X 101 M-'was determined, with the help of FN Briggs, in solutions similar to those used for skinned fibers and was the same for 100 and 300 mM KC1.