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Enhancing effect of calmodulin on Ca(2+)‐induced Ca2+ release in the sarcoplasmic reticulum of rabbit skeletal muscle fibres.
Author(s) -
Ikemoto T,
Iino M,
Endo M
Publication year - 1995
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 - 10.1113/jphysiol.1995.sp020901
Subject(s) - endoplasmic reticulum , calmodulin , rabbit (cipher) , skeletal muscle , biophysics , chemistry , calcium , ryanodine receptor 2 , lagomorpha , microbiology and biotechnology , anatomy , endocrinology , biochemistry , biology , ryanodine receptor , organic chemistry , statistics , mathematics
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.