Enhancing effect of calmodulin on Ca(2+)-induced Ca2+ release in the sarcoplasmic reticulum of rabbit skeletal muscle fibres

J Physiol. 1995 Sep 15;487 ( Pt 3)(Pt 3):573-82. doi: 10.1113/jphysiol.1995.sp020901.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Caffeine / pharmacology
  • Calcium / metabolism*
  • Calcium / pharmacology*
  • Calcium Channels / drug effects
  • Calcium Channels / metabolism
  • Calmodulin / pharmacology*
  • Cytophotometry
  • In Vitro Techniques
  • Magnesium / physiology
  • Male
  • Muscle Fibers, Skeletal / drug effects
  • Muscle Fibers, Skeletal / metabolism*
  • Muscle Fibers, Skeletal / ultrastructure
  • Muscle Proteins / drug effects
  • Muscle Proteins / metabolism
  • Muscle, Skeletal / drug effects
  • Muscle, Skeletal / metabolism*
  • Muscle, Skeletal / ultrastructure
  • Phosphodiesterase Inhibitors / pharmacology
  • Psoas Muscles / drug effects
  • Psoas Muscles / metabolism
  • Psoas Muscles / ultrastructure
  • Rabbits
  • Ryanodine Receptor Calcium Release Channel
  • Saponins / pharmacology
  • Sarcoplasmic Reticulum / drug effects
  • Sarcoplasmic Reticulum / metabolism*


  • Calcium Channels
  • Calmodulin
  • Muscle Proteins
  • Phosphodiesterase Inhibitors
  • Ryanodine Receptor Calcium Release Channel
  • Saponins
  • Caffeine
  • Magnesium
  • Calcium