Evidence of a role for calmodulin in the regulation of calcium release from skeletal muscle sarcoplasmic reticulum
The effect of calmodulin and calmodulin inhibitors on the Ca2+ release channel of heavy skeletal muscle sarcoplasmic reticulum (SR) vesicles was investigated. SR vesicles were passively loaded with 45Ca2+ in the presence of calmodulin and its inhibitors, followed by measurement of 45Ca2+ release rates by means of a rapid-quench-Millipore filtration method. Calmodulin at a concentration of 2-10 microM reduced 45Ca2+ efflux rates from passively loaded vesicles by a factor of 2-3 in media containing 10(-6)-10(-3) M Ca2+. At 10(-9) M Ca2+, calmodulin was without effect. 45Ca2+ release rates were varied 1000-fold (k1 approximately equal to 0.1-100 s-1) by using 10(-5) M Ca2+ with either Mg2+ or the ATP analogue adenosine 5'-(beta,gamma-methylenetriphosphate) in the release medium. In all instances, a similar 2-3-fold reduction in release rates was observed. At 10(-5) M Ca2+, 45Ca2+ release was half-maximally inhibited by about 2 X 10(-7) M calmodulin, and this inhibition was reversible. Heavy SR vesicle fractions contained 0.1-02 micrograms of endogenous calmodulin/mg of vesicle protein. However, the calmodulin inhibitors trifluoperazine, calmidazolium, and compound 48/80 were without significant effect on 45Ca2+ release at concentrations which inhibit calmodulin-mediated reactions in other systems. Studies with actively loaded vesicles also suggested that heavy SR vesicles contain a Ca2+ permeation system that is inhibited by calmodulin.
- Research Organization:
- Univ. of North Carolina, Chapel Hill
- OSTI ID:
- 5739207
- Journal Information:
- Biochemistry; (United States), Vol. 1
- Country of Publication:
- United States
- Language:
- English
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CALCIUM
MEMBRANE TRANSPORT
SARCOPLASMIC RETICULUM
CALCIUM 45
CATTLE
IMIDAZOLES
INHIBITION
MAGNESIUM
MUSCLES
RABBITS
TRACER TECHNIQUES
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METALS
ANIMALS
AZOLES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CALCIUM ISOTOPES
CELL CONSTITUENTS
DAYS LIVING RADIOISOTOPES
DOMESTIC ANIMALS
ELEMENTS
EVEN-ODD NUCLEI
HETEROCYCLIC COMPOUNDS
INTERMEDIATE MASS NUCLEI
ISOTOPE APPLICATIONS
ISOTOPES
MAMMALS
METALS
NUCLEI
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANOIDS
RADIOISOTOPES
RUMINANTS
VERTEBRATES
551001* - Physiological Systems- Tracer Techniques