The presence and binding characteristics of calmodulin in microsomal preparations enriched in sarcoplasmic reticulum from rabbit skeletal muscle.
ATP-dependent oxalate facilitated calcium transport in sarcoplasmic reticulum (SR) preparations obtained from rabbit vastus lateralis muscle (fast skeletal muscle; Fsr) and soleus (slow skeletal muscle; Ssr) was determined. Addition of exogenous calmodulin did not stimulate calcium transport in either Fsr or Ssr preparations. Fsr and Ssr previously washed in 1 mM EGTA demonstrated a reduced capacity to transport Ca2+; the exogenous addition of calmodulin (0.24 microM) under these conditions, did not restore uptake activity but significantly decreased the steady-state level of Ca2+ uptake. Extracts of skeletal SR prepared by treatment with 0.2 mM EDTA and boiling produced significantly more stimulation of red cell Ca2+ATPase activity than extracts prepared by boiling alone. This stimulation of red cell Ca2+-ATPase was inhibited to a significant extent by 48/80, a known anti-calmodulin agent. Radioimmunoassay revealed that extracts prepared by boiling or EDTA-treatment followed by boiling contained considerable amounts of calmodulin. Washing with 1 mM EGTA, though, did not release any calmodulin from SR. These studies reveal that calmodulin is present in both Fsr and Ssr and can only be removed by harsh treatments. The role of calmodulin in skeletal muscle Ca2+-transport remains to be determined.
D000818:Animals; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism*; D008861:Microsomes / Q000378:metabolism; D009132:Muscles / Q000378:metabolism* / Q000648:ultrastructure; D011817:Rabbits; D011863:Radioimmunoassay; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
D002147:Calmodulin; D000252:Calcium-Transporting ATPases