Inotropic support for hearts progressing towards failure represents an unmet need. Direct attempts to improve systolic function by activating -adrenergic receptor (-AR) signaling increases associated risk of heart failure and death. Calcitropes (agents influencing Ca2+ handling) that bypass -AR signaling are not necessarily proarrhythmic. Our working global hypothesis based on our recent and ongoing work studying RAD regulation of the L-type Ca2+ channel (LTCC) is that bypassing -AR signaling to increase Ca2+-induced Ca2+ release (CICR) provides safe, stable gain of function to counter heart failure progression. In this application we focus on the mechanisms of Rad – LTCC interactions as a novel means to instill inotropic support to the heart. The LTCC is a macromolecular hub that integrates multiple signaling pathways including protein kinase A (PKA) and Ca2+- calmodulin kinase II (CaMKII). RAD is a member of the RGK family of monomeric G-proteins. RAD binds to auxiliary CaV2 and CaV1.2, the pore-forming subunit of the LTCC. Deletion, or phosphorylation of RAD causes LTCC current (ICa,L) modulation and facilitation. Modulation of ICa,L is commonly observed after -AR signaling to activate PKA; facilitation is caused by CaMKII activation. In Specific Aim 1 we will dissect how RAD integrates each of these signaling pathways using a combination of pharmacological and genetic approaches. In Specific Aim 2 we will explore RAD – CaV1.2 structure-function using knock-in models of genetically modified mice that allow us to explore RAD – LTCC effects retaining native stoichiometry of the LTCC heteromultimeric protein complex. Specific Aim 3 explores RAD – LTCC interplay as an approach to attenuate progression of heart failure. To achieve these goals, we will integrate findings among Aims using in vivo, ex vivo and cellular/molecular approaches in animal models. Ex vivo human heart slices will be tested to evaluate the translational potential of RAD – LTCC regulation in heart health and disease.