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Ryanodine stores and calcium regulation in the inner segments of salamander rods and cones
Author(s) -
Krizaj David,
Lai F. Anthony,
Copenhagen David R.
Publication year - 2003
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2003.00761.x
Subject(s) - calcium , ryanodine receptor , biology , salamander , microbiology and biotechnology , regeneration (biology) , hormone , medicine , endocrinology , zoology
Despite the prominent role played by intracellular Ca 2+ stores in the regulation of neuronal Ca 2+ homeostasis and in invertebrate photoreception, little is known about their contribution to the control of free Ca 2+ concentration ([Ca 2+ ] i ) in the inner segments of vertebrate photoreceptors. Previously, caffeine‐sensitive intracellular Ca 2+ stores were shown to play a role in regulating glutamate release from photoreceptors. To understand the properties of these intracellular stores better we used pharmacological approaches that alter the dynamics of storage and release of Ca 2+ from intracellular compartments. Caffeine evoked readily discernible changes in [Ca 2+ ] i in the inner segments of rods, but not cones. Caffeine‐evoked Ca 2+ responses in cone inner segments were unmasked in the presence of inhibitors of the plasma membrane Ca 2+ ATPases (PMCAs) and mitochondrial Ca 2+ sequestration. Caffeine‐evoked responses were blocked by ryanodine, a selective blocker of Ca 2+ release and by cyclopiazonic acid, a blocker of Ca 2+ sequestration into the endoplasmic reticulum. These two inhibitors also substantially reduced the amplitude of depolarization‐evoked [Ca 2+ ] i increases, providing evidence for Ca 2+ ‐induced Ca 2+ release (CICR) in rods and cones. The magnitude and kinetics of caffeine‐evoked Ca 2+ elevation depended on the basal [Ca 2+ ] i , PMCA activity and on mitochondrial function. These results reveal an intimate interaction between the endoplasmic reticulum, voltage‐gated Ca 2+ channels, PMCAs and mitochondrial Ca 2+ stores in photoreceptor inner segments, and suggest a role for CICR in the regulation of synaptic transmission.