Characteristics of phosphate-induced Ca(2+) efflux from the SR in mechanically skinned rat skeletal muscle fibers.
The effects of P(i) on sarcoplasmic reticulum (SR) Ca(2+) regulation were studied in mechanically skinned rat skeletal muscle fibers. Brief application of caffeine was used to assess the SR Ca(2+) content, and changes in concentration of Ca(2+) ([Ca(2+)]) within the cytosol were detected with fura 2 fluorescence. Introduction of P(i) (1-40 mM) induced a concentration-dependent Ca(2+) efflux from the SR. In solutions lacking creatine phosphate (CP), the amplitude of the P(i)-induced Ca(2+) transient approximately doubled. A similar potentiation of P(i)-induced Ca(2+) release occurred after inhibition of creatine kinase (CK) with 2,4-dinitrofluorobenzene. In the presence of ruthenium red or ryanodine, caffeine-induced Ca(2+) release was almost abolished, whereas P(i)-induced Ca(2+) release was unaffected. However, introduction of the SR Ca(2+) ATPase inhibitor cyclopiazonic acid effectively abolished P(i)-induced Ca(2+) release. These data suggest that P(i) induces Ca(2+) release from the SR by reversal of the SR Ca(2+) pump but not via the SR Ca(2+) channel under these conditions. If this occurs in intact skeletal muscle during fatigue, activation of a Ca(2+) efflux pathway by P(i) may contribute to the reported decrease in net Ca(2+) uptake and increase in resting [Ca(2+)].
Duke
A M
AM
School of Biology, University of Leeds, Leeds, LS2 9JT United Kingdom.
Steele
D S
DS
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000493:pharmacokinetics*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D004396:Coloring Agents / Q000494:pharmacology; D004139:Dinitrofluorobenzene / Q000494:pharmacology; D015226:Dinucleoside Phosphates / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008856:Microscopy, Fluorescence; D018763:Muscle Fatigue / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000201:enzymology*; D018482:Muscle, Skeletal / Q000166:cytology* / Q000201:enzymology; D010725:Phosphocreatine / Q000494:pharmacology*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010758:Phosphorus / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012430:Ruthenium Red / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
D004396:Coloring Agents; D015226:Dinucleoside Phosphates; D004791:Enzyme Inhibitors; D010726:Phosphodiesterase Inhibitors; D010725:Phosphocreatine; D012430:Ruthenium Red; D012433:Ryanodine; C013907:cytidylyl adenosine; D010758:Phosphorus; D002110:Caffeine; D000244:Adenosine Diphosphate; D004139:Dinitrofluorobenzene; D000252:Calcium-Transporting ATPases; D002118:Calcium