Abstract
Cyclic adenosine monophosphate (cAMP) is a critical second messenger in cardiomyocytes, regulating essential cellular functions. Upon G-protein-coupled receptor stimulation, adenylyl cyclase (AC) synthesizes cAMP, which phosphodiesterase (PDE) enzymes subsequently degrade. Recent studies challenge the traditional view of uniform cAMP signaling, revealing nanodomain-specific regulation within cardiomyocytes. This localized cAMP signaling modulates key Ca(2+)-handling proteins, including ryanodine receptor type-2 (RyR2), through channel-bound protein kinases and PDEs. Additionally, nucleoside-diphosphate kinases (NDPKs), particularly NDPK-C, contribute to cAMP synthesis and RyR2 regulation. Elevated NDPK-C levels in failing hearts correlate with increased cAMP levels, enhanced sarcoplasmic reticulum Ca(2+) release, and cardiac arrhythmias. Furthermore, cAMP influences the expression of Ca(2+)-handling proteins. This review examines the mechanisms governing cAMP levels in the sarcoplasmic reticulum nanodomain and their role in regulating RyR2 function in healthy and diseased hearts.