Title: Co-activation of inositol trisphosphate-induced Ca2+ release by cytosolic Ca2+ is loading-dependent
Authors: Missiaen, Ludwig ×
De Smedt, Humbert
Parys, Jan
Casteels, Rik #
Issue Date: Apr-1994
Series Title: Journal of Biological Chemistry vol:269 issue:10 pages:7238-42
Abstract: Luminal and cytosolic Ca2+ control the sensitivity of the intracellular Ca2+ stores to inositol 1,4,5-trisphosphate (InsP3). In this work, we have characterized how luminal Ca2+ interfered with the stimulation of the InsP3 receptor by cytosolic Ca2+ in permeabilized A7r5 smooth muscle cells. InsP3-induced Ca2+ release from stores containing 34 pmol of Ca2+/10(6) cells absolutely depended on a simultaneous rise in cytosolic Ca2+ concentration in the submicromolar range. This stimulation by cytosolic Ca2+ was more pronounced when the stores were preincubated with Ca2+. In contrast, fully loaded stores containing 3400 pmol of Ca2+/10(6) cells already responded to InsP3 in the absence of cytosolic Ca2+ and the release from these stores was much less stimulated by increasing the cytosolic Ca2+ concentration. The loading dependence of the release was not due to a higher cytosolic Ca2+ concentration around more loaded stores sensitizing the InsP3 receptor by binding at a cytoplasmic site. Luminal Ca2+ was therefore found to functionally substitute for cytosolic Ca2+ in triggering Ca2+ release in the presence of a constant InsP3 concentration. These findings are relevant for explaining base-line Ca2+ spiking in non-excitable cells.
ISSN: 0021-9258
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Physiology Section (-)
Pharmacology Section (-)
Laboratory of Molecular and Cellular Signaling
× corresponding author
# (joint) last author

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