# Multiparametric imaging of spatio-temporal cAMP signaling, transmembrane potential, and intracellular calcium in the intact heart

## TL;DR

This paper introduces a new imaging system to study heart signaling molecules like cAMP in real time, revealing how they respond to nerve stimulation and affect heart function.

## Contribution

A novel multiparametric imaging system is developed to simultaneously monitor cAMP, transmembrane potential, and calcium in intact hearts with high spatiotemporal resolution.

## Key findings

- cAMP is strongly and heterogeneously activated in the heart in response to β-adrenergic receptor stimulation.
- The system tracks heart rate, action potential duration, and calcium responses alongside cAMP activity.
- Sympathetic and parasympathetic responses are quantified in atria and ventricles.

## Abstract

The spatiotemporal dynamics of intracellular second messengers and signaling molecules, including cyclic adenosine monophosphate (cAMP), have been studied extensively in isolated cardiomyocytes using Förster resonance energy transfer (FRET)-based reporters. However, approaches for linking cellular signaling to tissue-level function are limited. Here, we present a multiparametric imaging system that simultaneously records four wavelengths to visualize cAMP activity alongside real-time transmembrane potential and intracellular Ca2+ in intact hearts from a cardiac-specific cAMP reporter mouse. We showed that cAMP is strongly and heterogeneously activated throughout the heart (atria and ventricles) in response to pharmacological or nerve-activated β-adrenergic receptor stimulation, the time course of which matches heart rate, action potential, and Ca2+ responses. This multiparametric imaging system will provide insight into the relationship between cAMP signaling, electrophysiology, and arrhythmogenesis at high spatiotemporal resolution.

•Validated multiparametric imaging of cAMP, Vm, and Ca2+ in intact hearts•cAMP FRET acquired with and without excitation-contraction uncoupling•β-AR stimulation triggers heterogeneous cAMP while tracking HR, APD, and Ca2+•Quantification of sympathetic and parasympathetic responses in atria and ventricles

Validated multiparametric imaging of cAMP, Vm, and Ca2+ in intact hearts

cAMP FRET acquired with and without excitation-contraction uncoupling

β-AR stimulation triggers heterogeneous cAMP while tracking HR, APD, and Ca2+

Quantification of sympathetic and parasympathetic responses in atria and ventricles

Molecular physiology; Bioengineering; Experimental models in systems biology