© 2003 by European Society of Cardiology
Copyright © 2003, European Society of Cardiology
Cytosolic calcium in the ischemic rabbit heart: assessment by pH- and temperature-adjusted rhod-2 spectrofluorometry
aUniversität Rostock, Department of Cardiac Surgery, Schillingallee 35, 18057 Rostock, Germany
bChildren’s Hospital Boston, Department of Cardiac Surgery, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
cDepartment of Biostatistics, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
dDepartment of Anesthesiology, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
christof.stamm{at}med.uni-rostock.de
* Corresponding author. Tel.: +49-381-494-6101; fax: +49-381-494-6102.
Objectives: Cytosolic calcium ([Ca2+]i) mediates ischemia–reperfusion (I/R) injury, but magnitude and time course of I/R-induced [Ca2+]i overload remain unclear. Fluorescent indicators are commonly used to measure [Ca2+]i, and have a dissociation constant (Kd) that depends on pH and temperature. We hypothesized that changes of Kd during I/R lead to misleading interpretations of [Ca2+]i recordings. Methods: (1) In isolated rabbit hearts (n=4 each), intracellular pH was measured during I/R at 37°C, 20°C, and 4°C with and without cardioplegic arrest by 31P-NMR-spectroscopy. (2) Kd for rhod-2 and calcium was determined at varying pH and temperature in in vitro experiments. (3) Isolated rabbit hearts were subjected to I/R, and [Ca2+]i was recorded by surface rhod-2 spectrofluorometry. Finally, [Ca2+]i was computed using either the conventional Kd, or the pH- and temperature-adjusted Kd. Results: Kd(Ca2+Rhod-2) remained stable between pH 7.1 and 6.8, but increased exponentially with lower pH and/or temperature. Calculations using a static Kd indicated that [Ca2+]i rose only mildly during warm ischemia and did not rise during cardioplegic arrest, while a large Ca2+ influx appeared to occur during early reperfusion. When the pH and temperature-adjusted Kd was used for calculation, [Ca2+]i rose significantly during ischemia (431±37% during 20 min 37°C ischemia, and 78±19% during 20 min cardioplegic arrest at 20°C). During early reperfusion, [Ca2+]i decreased rapidly, without significant further [Ca2+]i elevation. Conclusions: In contrast to previous reports, [Ca2+]i accumulation occurs during unprotected ischemia as well as hypothermic ischemia with cardioplegic arrest, without further net Ca2+ influx on reperfusion. This finding has important implications for timing of protective strategies during myocardial ischemia.
KEYWORDS Calcium (cellular); Ischemia; Cardioplegia; Cardiovascular surgery
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  H. K. Saini and N. S. Dhalla Defective calcium handling in cardiomyocytes isolated from hearts subjected to ischemia-reperfusion Am J Physiol Heart Circ Physiol, May 1, 2005; 288(5): H2260 - H2270. [Abstract] [Full Text] [PDF]
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