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Effects of creatine phosphate on Ca 2+ regulation by the sarcoplasmic reticulum in mechanically skinned rat skeletal muscle fibres
Author(s) -
Duke Adrian M.,
Steele Derek S.
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.1469-7793.1999.0447t.x
Subject(s) - endoplasmic reticulum , creatine , skeletal muscle , chemistry , phosphate , calcium , biophysics , medicine , endocrinology , anatomy , biochemistry , biology
1 The effect of creatine phosphate (PCr) on sarcoplasmic reticulum (SR) Ca 2+ regulation was studied in mechanically skinned skeletal muscle fibres from rat extensor digitorium longus (EDL). Preparations were perfused with solutions mimicking the intracellular milieu and the [Ca 2+ ] within the muscle was monitored continuously using fura‐2. 2 Brief application of 40 mM caffeine caused a transient increase in [Ca 2+ ] due to SR Ca 2+ release, and an associated tension response. Withdrawal of PCr resulted in (i) a slow transient release of Ca 2+ from the SR (ii) a marked prolongation of the descending phase of the caffeine‐induced fluorescence ratio transient and (iii) a decrease in the Ca 2+ transient amplitude to 69.2 ± 2.7% ( n = 16 ) of control responses. 3 Prolongation of the caffeine‐induced Ca 2+ transient also occurred following application of the SR Ca 2+ pump inhibitor cyclopiazonic acid (CPA). This suggests that (i) the descending phase of the caffeine‐induced Ca 2+ transient is dependent on the rate of Ca 2+ uptake by the SR and (ii) prolongation associated with PCr withdrawal may also reflect a decrease in the net Ca 2+ uptake rate. 4 The effects of PCr withdrawal were mimicked by addition of the creatine kinase (CK) inhibitor 2,4‐dinitro‐1‐fluorobenzene (DNFB). Hence, reducing the [PCr] may influence SR Ca 2+ regulation by limiting local ATP regeneration by endogenous CK. After treatment with DNFB, PCr withdrawal had no effect on the Ca 2+ transient, confirming that PCr does not have an additional direct effect on the SR. 5 The Ca 2+ efflux associated with PCr withdrawal was insensitive to ryanodine or Ruthenium Red, but was effectively abolished by pretreatment with the SR Ca 2+ pump inhibitor cyclopiazonic acid (CPA). This suggests that the Ca 2+ efflux associated with PCr withdrawal is independent of the SR Ca 2+ channel, but may involve reversal or inhibition of the Ca 2+ ATPase. 6 These data suggest that Ca 2+ regulation by the SR is strongly dependent on the supply of ATP via endogenous CK. Depletion of PCr may contribute to impaired SR Ca 2+ regulation known to occur in intact skeletal muscle under conditions of fatigue.