Figure 5: K180R does not change total SR Ca content.
Total SR Ca content was quantified by integration of NCX current elicited in response to rapid caffeine application. Following four brief membrane depolarizations from −70 mV to +10 mV at 2 Hz to ensure consistent SR Ca loading, caffeine (10 mM) was applied using a rapid solution exchanger for 15 s at a holding potential of −70 mV. Isoproterenol (1 µM) was added to the external solution to activate beta-adrenergic receptors. NCX current integrals were normalized by cell capacitance, a measure of cell size and expressed as pC/pF. A. Representative traces of the NCX currents from 3 groups. B. NCX integral summary data. WT n = 15 cells from 5 hearts; K180R HET n = 17 cells from 4 hearts; Casq2 KO n = 14 cells from 5 hearts. Data displayed as mean ± SD. Data analyzed using a hierarchical statistical model with Bonferroni correction.