Unique characteristics of Ca~(2+) homeostasis of the trans-Golgi compartment

摘要

Taking advantage of a fluorescent Ca~(2+) indicator selectively targeted to the trans-Golgi lumen, we here demonstrate that its Ca~(2+) homeostatic mechanisms are distinct from those of the other Golgi subcompartments: (ⅰ) Ca~(2+) uptake depends exclusively on the activity of the secretory pathway Ca~(2+) ATPasei (SPCA1), whereas the sarco-endoplasmic reticulum Ca~(2+) ATPase (SERCA) is excluded; (ⅱ) IP_3 generated by receptor stimulation causes Ca~(2+) uptake rather than release; (ⅲ) Ca~(2+) release can be triggered by activation of rya-nodine receptors in cells endowed with robust expression of the latter channels (e.g., in neonatal cardiac myocyte). Finally, we show that, knocking down the SPCA1, and thus altering the trans-Golgi Ca~(2+) content, specific functions associated with this subcompart-ment, such as sorting of proteins to the plasma membrane through the secretory pathway, and the structure of the entire Golgi apparatus are dramatically altered.