An intelligent sarco-endoplasmic reticulum Ca2+ store: release and leak channels have differential access to a concealed Ca2+ pool.
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(3)Rs) 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.
Guerrero-Hernandez
Agustin
A
Department of Biochemistry, Cinvestav-IPN, México City, DF, Mexico. aguerrero@cinvestav.mx
Dagnino-Acosta
Adan
A
Verkhratsky
Alexei
A
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D015220:Calcium Channels / Q000378:metabolism / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D006801:Humans; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism / Q000502:physiology; D012519:Sarcoplasmic Reticulum / Q000201:enzymology / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism / Q000502:physiology*
D015220:Calcium Channels; D019837:Ryanodine Receptor Calcium Release Channel; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002118:Calcium