Figure 3.

In vitro Takotsubo cardiomyopathy model induced by high dose epinephrine exposure. Effect of 20 min pretreatment with epinephrine (Epi-pre, 1µM), followed by 10 min wash, on subsequent β₂AR contractile (A) and cAMP (B) responses with Gi (PTX-sensitive) component. A, Contraction amplitude in isolated rat ventricular myocytes: peak fold increase over basal: Control (n=15); Epi-pretreated alone (n=15); Epi-pretreated +PTX (n=7). B, Whole cell cyclic AMP levels, measured using an EPAC2-FRET sensor. Control (n=40); Epi-pretreated alone (n=10); Epi-pretreated +PTX (n=9). *P<0.05, **P<0.01, ***P<0.001, one-way ANOVA Kruskal-Wallis test. C, β₂AR-mediated inotropic response to 100nM isoproterenol in the presence of the β₁AR blocker CGP20712A (300nM), peak fold increase over basal in control (n=13) or PTX-treated rat ventricular myocytes (n=13), in the presence and absence of SB20380 2.5μM. **P<0.01, ***P<0.001 vs control, unpaired t-test. D and E, Apically-derived cardiomyocytes demonstrate increased β₂AR levels and responses. D, Proportion of β₂ARs with respect to total βAR radioligand binding in ventricular myocytes from the apex and base of normal rat heart. N=4 preparations, **P<0.01 vs base, paired t-test. E, Apical cardiomyocytes (purple bars) show a larger increase in percentage cell shortening through the β₂AR compared to basal cardiomyocytes (green bars). Fold increase in shortening with 100nM isoproterenol + 300nM CGP20712A. (*p<0.05 apex vs base, paired t-test. Base: n=13 cells; Apex: n=13 cells, n=13 animals).