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. 2014 Jun 23;3(3):e000996. doi: 10.1161/JAHA.114.000996

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© 2014 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley Blackwell.

This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

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Figure 9. — β‐adrenergic stimulation speeds twitch duration and restores entrained rhythmicity in cardiomyocytes expressing relatively low Ca²⁺‐affinity long QT syndrome calmodulin (CaM) mutants. A, Stimulated twitch decay (1 Hz) at baseline and following 100 nmol/L ISO. *P<0.05. Ai, Regardless of exogenous CaM expression, the twitch decay rate was faster following ISO. Data from (A) replotted as cell‐by‐cell response to ISO.**P<0.001; ***P<10⁻⁴; n=10 or 11. B, Representative Ca²⁺ transient for D96V‐CaM expressing fetal ventricular myocyte. Left panel shows 1‐Hz stimulation to illustrate baseline 2:1 block. Right panel shows an example of partial restoration of entrainment of Ca²⁺ transient to field stimulation. With ISO, the 2:1 activity spontaneously reverts to 1:1 activity. n=10. C, Representative Ca²⁺ transient for D130G‐CaM expressing fetal ventricular myocyte. Left panel shows 0.5‐Hz stimulation to illustrate baseline alternans. Right panel shows an example of recovery of entrainment following ISO. n=10. ISO indicates isoproterenol, WT, wild type.