( Nor AC y÷o8-tyy SL Ca channel ATP Ca2+ cAMP Ca pump PKA Troponin-1 Phospholamban SR cAMP signal ing in the heart ST indicates synaptic terminal;Nor,norepinephrine; SL,sarcolemma;AC,adenylyl cyclase;PKA,protein kinase A;and SR,sarcoplasmic reticulumcAMP signaling in the heart ST indicates synaptic terminal; Nor, norepinephrine; SL, sarcolemma; AC, adenylyl cyclase; PKA, protein kinase A; and SR, sarcoplasmic reticulum