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The Journal of Neuroscience, January 20, 2010, 30(3):950-957; doi:10.1523/JNEUROSCI.2894-09.2010

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Cellular/Molecular
Chromogranin B Gene Ablation Reduces the Catecholamine Cargo and Decelerates Exocytosis in Chromaffin Secretory Vesicles

Jésica Díaz-Vera,¹ Yézer G. Morales,¹ Juan R. Hernández-Fernaud,² Marcial Camacho,¹ Mónica S. Montesinos,¹ Federico Calegari,³ Wieland B. Huttner,³ Ricardo Borges,¹ and José D. Machado¹

¹Unit of Pharmacology, Medical School, and ²Proteomic Service, La Laguna University, 38071 La Laguna, Tenerife, Spain, and ³Max Planck Institute of Molecular Biology and Genetics, 01307 Dresden, Germany

Correspondence should be addressed to Dr. Ricardo Borges, Unidad de Farmacología, Facultad de Medicina, Universidad de La Laguna, 38071 La Laguna, Tenerife, Spain. Email: rborges{at}ull.es

Chromogranins/secretogranins (Cgs) are the major soluble proteins of large dense-core secretory vesicles (LDCVs). We have recently reported that the absence of chromogranin A (CgA) caused important changes in the accumulation and in the exocytosis of catecholamines (CAs) using a CgA-knock-out (CgA-KO) mouse. Here, we have analyzed a CgB-KO mouse strain that can be maintained in homozygosis. These mice have 36% less adrenomedullary epinephrine when compared to Chgb^+/+ [wild type (WT)], whereas the norepinephrine content was similar. The total evoked release of CA was 33% lower than WT mice. This decrease was not due to a lower frequency of exocytotic events but to less secretion per quantum (30%) measured by amperometry; amperometric spikes exhibited a slower ascending but a normal decaying phase. Cell incubation with L-DOPA increased the vesicle CA content of WT but not of the CgB-KO cells. Intracellular electrochemistry, using patch amperometry, showed that L-DOPA overload produced a significantly larger increase in cytosolic CAs in cells from the KO animals than chromaffin cells from the WT. These data indicate that the mechanisms for vesicular accumulation of CAs in the CgB-KO cells were saturated, while there was ample capacity for further accumulation in WT cells. Protein analysis of LDCVs showed the overexpression of CgA as well as other proteins apparently unrelated to the secretory process. We conclude that CgB, like CgA, is a highly efficient system directly involved in monoamine accumulation and in the kinetics of exocytosis from LDCVs.

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Received June 18, 2009; revised Nov. 10, 2009; accepted Nov. 16, 2009.

Correspondence should be addressed to Dr. Ricardo Borges, Unidad de Farmacología, Facultad de Medicina, Universidad de La Laguna, 38071 La Laguna, Tenerife, Spain. Email: rborges{at}ull.es

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