Figure 2.

Cardiomyocyte Ca²⁺ transient and spark properties in response to β-adrenergic agonist isoproterenol. A, Experimental protocol used for Ca²⁺ imaging, the gray bars represent when line-scan images were acquired. Representative line-scans during pacing (B) and resultant Ca²⁺ transients (C) from a WT and CaMKIIδ (Ca²⁺/calmodulin kinase II delta)-KO cardiomyocyte stimulated at 0.5 Hz under control conditions and with 100 nmol/L ISO. ISO increased Ca²⁺ transient amplitude (D) and accelerated decay (E) in both WT and CaMKIIδ-KO cardiomyocytes to a similar degree (WT n=8 cells, N=2 hearts; CaMKIIδ-KO n=13 cells, N=4 hearts). F, Representative line-scans from a WT and CaMKIIδ-KO cardiomyocyte show an increase in the number of Ca²⁺ sparks following exposure to ISO. Mean data show the ISO-induced increase in Ca²⁺ spark frequency (CaSpF) was attenuated in the CaMKIIδ-KO cardiomyocytes (G; WT: n=11 cells, N=2 hearts; CaMKIIδ-KO: n=13 cells, N=4 heats).