Do we know the absolute values of intracellular free calcium concentration?

More than 20 years ago, it was shown that the addition of EGTA increases the affinity of the plasma membrane Ca 2+ pump for Ca 2+ by an order of magnitude. The left-hand shift of Ca 2+-dependencies in the presence of EGTA has been also documented in studies of the sarcoplasmic reticulum Ca 2+ pump,...

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Bibliographic Details
Published in:Cell calcium (Edinburgh) 2003-12, Vol.34 (6), p.511-515
Main Authors: Orlov, Sergei N, Grygorczyk, Ryszard, Kotelevtsev, Sergei V
Format: Article
Language:English
Subjects:
Aminoquinolines
Ca 2+-binding
Ca 2+-transport
Calcium - metabolism
Calcium - standards
Calcium-Transporting ATPases - metabolism
Calmodulin - metabolism
Cell Membrane - metabolism
Chelating Agents - pharmacology
Egtazic Acid - pharmacology
Fluorescent Ca 2+ indicators
Fluorescent Dyes
Indicators and Reagents
Intracellular Fluid - chemistry
Intracellular Fluid - metabolism
Polyvalent cations
Reference Standards
Sarcoplasmic Reticulum - enzymology
Sarcoplasmic Reticulum - metabolism
Troponin C - metabolism
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Summary:More than 20 years ago, it was shown that the addition of EGTA increases the affinity of the plasma membrane Ca 2+ pump for Ca 2+ by an order of magnitude. The left-hand shift of Ca 2+-dependencies in the presence of EGTA has been also documented in studies of the sarcoplasmic reticulum Ca 2+ pump, mitochondrial Ca 2+-transporter as well as Ca 2+-binding by calmodulin and troponin C. These data allow us to hypothesise that this effect is caused by an admixture of di- and trivalent cations possessing high affinity for EGTA and interacting with Ca 2+-transporting and binding proteins. Here, we propose that polyvalent cations affect the estimation of absolute values of free intracellular Ca 2+ concentration. Indeed, EGTA sharply increases the apparent affinity of the fluorescent Ca 2+ indicators quin-2 and fluo-3 for Ca 2+. The impact of polyvalent cations on Ca 2+ measurement was further confirmed by the study showing the high sensitivity of Ca 2+-induced fluo-3 fluorescence to Mn 2+, Fe 2+, Cu 2+, and Co 2+ seen in the absence of EGTA.
ISSN:0143-4160
1532-1991
DOI:10.1016/S0143-4160(03)00125-8