Calcium transient alternans in blood-perfused ischemic hearts: observations with fluorescent indicator fura red.
Ischemia produces striking electrophysiological abnormalities in blood-perfused hearts that may be caused, in part, by effects of ischemia on intracellular calcium. To test this hypothesis, intracellular Ca2+ concentration ([Ca2+]i) transients were recorded from the epicardial surface of blood- and saline-perfused rabbit hearts using the long-wavelength indicator Fura Red. Calcium transients were much larger than the movement artifact, representing up to 29% of the total signal. Switching the perfusate from saline to blood did not affect the time course of the transients or the apparent level of [Ca2+]i. Compartmentation of Fura Red fluorescence was estimated by exposure to Mn2+. The results were cytosol 60 +/- 3%, organelles 12 +/- 2%, and autofluorescence plus partly deesterified Fura Red 29 +/- 4%. [Ca2+]i transients were calibrated in situ by perfusion of the extracellular space with high-Ca2+ and Ca(2+)-free EGTA solutions. Peak systolic [Ca2+]i was 663 +/- 74 nM, and end-diastolic [Ca2+]i was 279 +/- 59 nm. Ischemia was produced by interruption of aortic perfusion for 2.5 min during pacing (150 beats/min). Ischemia produced broadening of the [Ca2+]i transient, along with beat-to-beat alternations in the peak systolic and end-diastolic level of [Ca2+]i (calcium transient alternans). [Ca2+]i transient alternans occurred in 82% of blood-perfused hearts vs. 43% of saline-perfused hearts. The discrepancy between large and small transients (mean alternans ratio) was larger in the blood-perfused hearts (0.23 +/- 0.04 vs. 0.07 +/- 0.03, P = 0.005). These observations are important because of the apparent relationship of [Ca2+]i transient alternans to electrical alternans and arrhythmias during ischemia.
Wu
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Y
Cardiology Division, Stanford University School of Medicine, California 94305, USA.
Clusin
W T
WT
D000818:Animals; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism*; D002138:Calibration; D005260:Female; D005456:Fluorescent Dyes; D006321:Heart / Q000187:drug effects / Q000502:physiology / Q000503:physiopathology; D007093:Imidazoles; D015759:Ionomycin / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008345:Manganese / Q000494:pharmacology; D017202:Myocardial Ischemia / Q000503:physiopathology*; D009206:Myocardium / Q000378:metabolism*; D011817:Rabbits; D013050:Spectrometry, Fluorescence / Q000379:methods; D013347:Subcellular Fractions / Q000378:metabolism; D013997:Time Factors
D001572:Benzofurans; D005456:Fluorescent Dyes; D007093:Imidazoles; C082877:fura red; D008345:Manganese; D015759:Ionomycin; D002118:Calcium