Figure 2. Cardiac deletion of SAP97 enhances adrenergic stimulation of CaMKII and E-C coupling.

A) The expression of membrane β₁AR in 2-month old SAP97-f/f and SAP97-cKO hearts was quantified with radioligand binding assay. B) Cardiac β₁AR was immunoprecipitated in 10-month old SAP97-f/f and SAP97-cKO heart lysates. The pulled down proteins were subjected to detection of CaMKII, Epac2, arrestin2, and β₁AR. ** p < 0.01 by t-test. C) Western blots show total and phosphorylated CaMKII at Threonine 286 in 2-month old SAP97-f/f and SAP97-cKO heart lysates. * p < 0.05 by student t-test. D) Cardiac ejection fraction was measured at baseline and after stimulation with 2 μg/kg and 200 μg/kg of isoproterenol in 2-month old SAP97-f/f (n = 4) and SAP97-cKO (n = 5) mice. * p < 0.05 by t-test compared to SAP97-f/f controls. E) SAP97-f/f and SAP97-cKO AVMs from 2-month old mice were stimulated with 100 nmol/L of isoproterenol, total and phosphorylated CaMKII were detected in western blots. * p < 0.05 by one-way ANOVA followed by Tukey’s test. F-G) SAP97-f/f and SAP97-cKO AVMs from 2-month old mice were pretreated with 1 μmol/L of H89 and KN93 as indicated before stimulation with 100 nmol/L of isoproterenol. Myocyte contractile shortening was recorded before and after isoproterenol stimulation. Data were 2–5 repeated measurements of cells from 5–6 mice. * p < 0.05, **p < 0.01, and ***p < 0.001 by one-way nested ANOVA followed by Tukey’s test.