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Influence of inorganic phosphate and pH on sarcoplasmic reticular ATPase in skinned muscle fibres of Xenopus laevis
Author(s) -
Stienen G. J. M.,
Papp Z.,
Zaremba R.
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.0735p.x
Subject(s) - chemistry , atpase , pi , isometric exercise , myofibril , sarcoplasm , biophysics , phosphate , biochemistry , medicine , endoplasmic reticulum , enzyme , biology
1 The influence of 30 mM inorganic phosphate (P i ) and pH (6.2‐7.4) on the rate of ATP utilization was determined in mechanically skinned bundles of myofibrils from the iliofibularis muscle of Xenopus laevis at approximately 5 °C. 2 BDM (2,3‐butanedione monoxime; 10 mM) depressed isometric force production and actomyosin (AM) ATPase activity equally. Therefore sarcoplasmic reticular (SR) ATPase activity could be determined by extrapolation of the total ATPase activity to zero force. 3 The SR ATPase activity without added P i at pH 7.1 was 42 ± 2 % of the total ATPase activity. Addition of 30 mM P i reduced SR ATPase activity slightly, by 9 ± 5 %, and depressed force by 62 ± 2 % and AM ATPase activity by 21 ± 6 %. 4 At pH 6.2, force, SR ATPase activity and AM ATPase activity were reduced by 21 ± 5, 61 ± 5 and 10 ± 4 % of their respective values at pH 7.1. 5 The SR ATPase activity at 30 mM P i and pH 6.2 was reduced markedly to 20 ± 6 % of the value under control conditions, suggesting that the maximum rate of Ca 2+ uptake during muscle fatigue was strongly depressed. This reduction was larger than expected on the basis of the effects of P i and pH alone.