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Figure 4 | BioMedical Engineering OnLine

Figure 4

From: Ratiometric imaging of calcium during ischemia-reperfusion injury in isolated mouse hearts using Fura-2

Figure 4

Rapid reversible changes to Ca2+ homeostasis occur during ischemia. Hearts loaded with Fura-2 AM were subjected to a rapid pacing protocol consisting of a train of 2 ms wide S1 pulses at a cycle length of 150 ms. Pacing was continuously supplied through 5 minutes of normal heart activity, 15 minutes of ischemia and a further 15 minutes of reperfusion. Recordings of Ca2+ fluorescence and NADH autofluorescence were taken periodically throughout this time. During recordings alone, the pacing protocol was changed to introduce a 500 ms pause to allow calculation of the time constant of decay; when the recording was complete, steady state S1 pacing was resumed. Immediately following each Fura-2 recording, a second independent recording of flavin autofluorescence was made with an excitation wavelength of 460 nm to allow estimation of the contribution of NADH autofluorescence. (A) A representative recording of Ca2+ transients resulting from this protocol and the corresponsing stimulus pulses, each 2 ms wide at an amplitude twice the stimulation threshold (Ithresh). (B) Single exponent fits of Ca2+ transient decays in the MI region indicate a slowing of the SR Ca2+ ATP-ase pump during ischemia which recovers during reperfusion. (C, D) NADH-corrected Fura-2 ratios indicate a moderate 40% increase in diastolic Ca2+ and 25% increase in systolic Ca2+ in the MI region. (E, F) Accounting for the pH-dependent changes in kd that accompany ischemia shows the dramatic increase in both diastolic and systolic Ca2+ during ischemia in the MI region; both variables normalize during reperfusion.

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