No abstract

Ca 2+ release from the Golgi apparatus regulates key functions of the organelle, including vesicle trafficking. However, the signaling pathways that control this form of Ca 2+ release are poorly understood and evidence of discrete Golgi Ca 2+ release events is lacking. Here, we identified the Golgi apparatus as the source of prolonged Ca 2+ release events that originate from the nuclear 'poles' of primary cardiac cells. Once initiated, Golgi Ca 2+ release was unaffected by global depletion of sarcoplasmic reticulum Ca 2+ , and disruption of the Golgi apparatus abolished Golgi Ca 2+ release without affecting sarcoplasmic reticulum function, suggesting functional and anatomical independence of Golgi and sarcoplasmic reticulum Ca 2+ stores. Maximal activation of β 1 -adrenoceptors had only a small stimulating effect on Golgi Ca 2+ release. However, inhibition of phosphodiesterase (PDE) 3 or 4, or downregulation of PDE 3 and 4 in heart failure markedly potentiated β 1 -adrenergic stimulation of Golgi Ca 2+ release, consistent with compartmentalization of cAMP signaling within the Golgi apparatus microenvironment. β 1 -adrenergic stimulation of Golgi Ca 2+ release involved activation of both Epac and PKA signaling pathways and CaMKII. Interventions that stimulated Golgi Ca 2+ release induced trafficking of vascular growth factor receptor-1 (VEGFR-1) from the Golgi apparatus to the surface membrane. These data establish the Golgi apparatus as a juxtanuclear focal point for Ca 2+ and β 1 -adrenergic signaling, which functions independently from the sarcoplasmic reticulum and the global Ca 2+ transients that underlie the primary contractile function of the cell. *To whom correspondence should be addressed: d.steele@leeds.ac.uk. Author contributions: Yang: confocal Ca 2+ imaging and DAF-2 experiments; Kirton: Ca 2+ imaging and immunofluorescence experiments. MacDougall: Western blot analysis; Boyle: Immunofluorescence measurements; Deuchars: electron microscopy; Frater: electron microscopy; Ponnambalan immunofluorescence experiments and experimental design; Hardy: preparation of heart failure model; White: preparation of heart failure model; Calaghan Western blot analysis and experimental design; Peers: experimental design, immunofluorescence and editing of draft manuscript; Steele: Experimental design, manuscript preparation and overall project management.