Enhancing effect of calmodulin on Ca(2+)-induced Ca2+ release in the sarcoplasmic reticulum of rabbit skeletal muscle fibres.
1. We analysed the effect of calmodulin on Ca(2+)-induced Ca2+ release (CICR) in the sarcoplasmic reticulum (SR) using chemically skinned fibres of rabbit psoas muscle. Ca2+ release was measured using fura-2 microfluorometry. 2. In saponin-skinned fibres, calmodulin potentiated Ca2+ release at low Ca2+ concentrations (< 3 microM), while it showed an inhibitory effect at high Ca2+ concentrations (3-30 microM). 3. Co-application of ryanodine and calmodulin at 0.3 microM Ca2+, but not ryanodine alone, induced a decline in the Ca2+ uptake capacity of the SR, an effect expected from the open-lock of active CICR channels by ryanodine. Thus, potentiation of Ca2+ release by calmodulin at low Ca2+ concentrations can be regarded as a result of the activation of the ryanodine receptor. 4. Greater concentrations of calmodulin were required for potentiation of CICR at low Ca2+ concentrations (1 microM) than for inhibition at high Ca2+ concentrations (10 microM). 5. In beta-escin-permeabilized fibres in which intrinsic calmodulin was retained, the rates of CICR were similar to those measured in the presence of 1 microM calmodulin in saponin-permeabilized fibres. 6. These results suggest that calmodulin plays an important role in the regulation of CICR channels in intact skeletal muscle fibres.
Ikemoto
T
T
Department of Pharmacology, Faculty of Medicine, University of Tokyo, Japan.
Iino
M
M
Endo
M
M
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002147:Calmodulin / Q000494:pharmacology*; D003592:Cytophotometry; D066298:In Vitro Techniques; D008274:Magnesium / Q000502:physiology; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D009124:Muscle Proteins / Q000187:drug effects / Q000378:metabolism; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D016658:Psoas Muscles / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D011817:Rabbits; D019837:Ryanodine Receptor Calcium Release Channel; D012503:Saponins / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*
D015220:Calcium Channels; D002147:Calmodulin; D009124:Muscle Proteins; D010726:Phosphodiesterase Inhibitors; D019837:Ryanodine Receptor Calcium Release Channel; D012503:Saponins; D002110:Caffeine; D008274:Magnesium; D002118:Calcium