BS-400-08 HETEROGENOUS CAMP SIGNALING IN THE INTACT HEART IS SEX DEPENDENT

Abstract

cAMP is key for transducing autonomic signals into downstream electrophysiological responses. Previous studies have shown intracellular heterogeneity and compartmentalization of cAMP signaling. Yet, if cAMP signaling occurs heterogeneously throughout the intact heart, and how this translates into functional responses, has not been explored. To determine the spatiotemporal kinetics of cAMP signaling in the intact heart and the underlying mechanisms responsible. Male and female cardiac-specific CAMPER reporter mice that report cAMP binding by changes in FRET were used at 12 weeks. Hearts were excised and Langendorff-perfused for simultaneous cAMP and Vm imaging on a novel integrated whole heart optical imaging system. Following perfusion, tissue samples from base and apex were assessed for phosphodiesterase (PDE) activity. In male hearts, cAMP was uniformly activated in response to β-AR stimulation with bolus norepinephrine (NE, 1.5 μM). Conversely, in female hearts NE led to a greater change in cAMP activity in basal regions vs. the apex (n=7, p<0.05). Moreover, cAMP deactivation was slower in the base vs. apex, in female (n=6, p<0.01) but not male hearts (n=6). Apex-base differences were also evident following PDE inhibition with IBMX (100 μM), with a greater change in cAMP activity in the apex vs. base in both female (n=7, p<0.001) and male hearts (n=5, p<0.05). Likewise, PDE activity assays showed higher total PDE activity in apical regions (n=10, p<0.01), with more apical PDE activity in female vs. male hearts (n=5, p<0.05). In female hearts, faster apical cAMP deactivation following bolus NE was associated with a significant difference in action potential duration (APD80) between apex and base (n=3, p<0.05), but APD80 was not significantly different between regions in male hearts. Using novel whole heart imaging, we have shown female hearts display lower maximal cAMP activity and faster deactivation in the apex, in part, due to elevated PDE activity in this region. This heterogeneity was not observed in male hearts. These findings may have important implications for electrophysiological responses regulated by the cAMP pathway, particularly in heart failure, where PDE activity is altered.