Extracellular calcium as an integrator of tissue function

• Published in: The international journal of biochemistry & cell biology Vol. 40; no. 8; pp. 1467 - 1480
• Main Author: Breitwieser, Gerda E.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 2008
• Subjects: Animals; Calcium - physiology; Calcium sensing receptor; Calcium Signaling - physiology; Extracellular calcium; Membrane Microdomains - physiology; Multicellular network; Receptors, Calcium-Sensing - physiology; Signal amplification; Signal integration; Ca i 2; NCX; Multicellular network; Ca o 2; PTH; Calcium sensing receptor; CaR; Extracellular calcium; GPCR; Signal integration; PMCA; Signal amplification; 1,25(OH) 2D
• ISSN: 1357-2725; 1878-5875
• DOI: 10.1016/j.biocel.2008.01.019

The past several decades of research into calcium signaling have focused on intracellular calcium (Ca i 2+), revealing both exquisite spatial and dynamic control of this potent second messenger. Our understanding of Ca i 2+ signaling has benefited from the evolution of cell culture methods, development of high affinity fluorescent calcium indicators (both membrane-permeant small molecules and genetically encoded proteins), and high-resolution fluorescence microscopy. As our understanding of single cell calcium dynamics has increased, translational efforts have attempted to push calcium signaling studies back into tissues, organs and whole animals. Emerging results from these more complicated, diffusion-limited systems have begun to define a role for extracellular calcium (Ca o 2+) as an agonist, spurred by the cloning and characterization of a G protein-coupled receptor activated by Ca o 2+ (the calcium sensing receptor, CaR). Here, we review the current state-of-the art for measurement of Ca o 2+ fluctuations, and the evidence that fluctuations in Ca o 2+ can act as primary signals regulating cell function. Current results suggest that Ca o 2+ in bone and epidermis may act as a chemotactic homing signal, targeting cells to the appropriate tissue locations prior to initiation of the differentiation program. Ca i 2+ signaling-mediated Ca o 2+ fluctuations in interstitial spaces may integrate cell signaling responses in multicellular networks through activation of CaR. Appreciation of the importance of Ca o 2+ fluctuations in coordinating cell function will likely spur identification of additional, niche-specific Ca 2+ sensors, and provide unique insights into the regulation of multicellular signaling networks.