Figure 5.

Long QT syndrome (LQTS) CaM mutant expression induces loss of field‐stimulation entrainment in rank order with Ca²⁺ affinity. A, Representative Ca²⁺ transients for pacing frequencies of 0.5, 1, and 2 Hz. B, Representative Ca²⁺ transient for a cardiomyocyte expressing D96V‐CaM showing 2:1 block. The stimulus frequency is 1 Hz, and individual stimuli are denoted by vertical lines below the Ca²⁺ transients. The red arrows above the Ca²⁺ transient show the stimuli that did not elicit a Ca²⁺ transient. C, Summary plot of the prevalence of escape from entrainment events in cardiomyocytes expressing exogenous WT CaM or LQTS‐CaM mutants. Higher stimulus frequency evoked a greater prevalence of escape events in rank order with Ca²⁺‐CaM affinity. For statistical testing, we lumped together escape events at 2 and 3 Hz, P<10⁻⁴. CaM indicates calmodulin; WT, wild type.