Interaction of different nucleotides with Ca-release channels from heavy sarcoplasmic reticulum

Calcium accumulation and release from the heavy fraction of sarcoplasmic reticulum vesicles have been studied in the presence of different nucleotides with the use of the Ca-sensitive dye antipyrylazo III for monitoring of the free Ca2+ concentration. The calcium- and caffeine-induced Ca2+ release is observed only with ATP but not with any of nonadenine nucleotides used as substrates for the Ca-pump. Adenine nucleotides provide for a rapid ruthenium red sensitive Ca2+ release from the vesicles, when nonadenine nucleotides are used as energy sources for Ca2+ uptake. A comparison of the nucleotides interaction with Ca-channels and Ca-ATPase supports the hypothesis that Ca-ATPase is involved in the operation of Ca-channels.