Abstract
Simultaneous recording of cytosolic and sarco-endoplasmic reticulum (SR/ER) luminal free calcium concentrations ([Ca 2+] i and [Ca 2+] L, respectively) supports the notion that release channels (RyRs and IP 3Rs) use a concealed Ca 2+ source, likely to be associated with intra-SR/ER Ca 2+ binding proteins, whereas SR/ER Ca 2+ leak channels can only access free luminal Ca 2+. We hypothesize that Ca 2+ is trapped by oligomers of luminal Ca 2+-binding proteins and that the opening of release channels induces the rapid liberation of this “concealed” Ca 2+ source associated with intra-ER Ca 2+ buffers. Our hypothesis may also clarify why SERCA pumps potentiate Ca 2+ release and explain quantal characteristics and refractory states of Ca 2+ release process.
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