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1 Heart and Vascular Research Center and the Department Biomedical Engineering, MetroHealth Campus, Case Western Reserve University, Cleveland, Ohio, USA
* To whom correspondence should be addressed. E-mail: klaurita{at}metrohealth.org.
Regional heterogeneities of ventricular repolarizing currents and their role in arrhythmogenesis have received much attention, however relatively little is known regarding heterogeneities of intracellular calcium handling. Since repolarization properties and contractile function are heterogeneous from base to apex of the intact heart, we hypothesize that calcium 5 handling is also heterogeneous from base to apex. Methods: To test this hypothesis, we developed a novel ratiometric optical mapping system capable of measuring calcium fluorescence of Indo-1 at two separate wavelengths from 256 sites simultaneously. Using intact Langendorff-perfused guinea pig hearts, ratiometric calcium transients were recorded under normal conditions and during administration of known inotropic agents. Results: Ratiometric 10 calcium transients were insensitive to changes in excitation light intensity and fluorescence over time. Under control conditions, calcium transient amplitude near the apex was significantly larger (60%, p<0.01) compared to the base. In contrast, calcium transient duration was significantly longer (7.5%, p<0.03) near the base compared to the apex. During Isoproterenol (0.05µM) and Verapamil (2.5µM) administration, ratiometric calcium transients accurately 15 reflected changes in contractile function; however, the direction of base to apex heterogeneities remained unchanged compared to control. Conclusions: Ratiometric optical mapping techniques can be used to accurately quantify heterogeneities of calcium handling in the intact heart. Significant heterogeneities of calcium release and sequestration exist from base to apex of the intact heart. These heterogeneities are consistent with base to apex heterogeneities of 20 contraction observed in the intact heart and may play a role in arrhythmogenesis under abnormal conditions.
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