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The Journal of Neuroscience, March 26, 2008, 28(13):3350-3358; doi:10.1523/JNEUROSCI.5292-07.2008

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Cellular/Molecular
The Crucial Role of Chromogranins in Storage and Exocytosis Revealed Using Chromaffin Cells from Chromogranin A Null Mouse

Monica S. Montesinos,^1 * J. David Machado,^1 * Marcial Camacho,^1 * Jesica Diaz,¹ Yezer G. Morales,¹ Diego Alvarez de la Rosa,¹ Emilia Carmona,² Agustin Castañeyra,² O. Humberto Viveros,¹ Daniel T. O'Connor,³ Sushil K. Mahata,³ and Ricardo Borges¹

¹Unit of Pharmacology and ²Department of Anatomy, Medical School, University of La Laguna, 38071 Tenerife, Spain, and ³Hypertension Research Unit 0838, University of California, San Diego, California 92161

Correspondence should be addressed to Dr. Ricardo Borges, Pharmacology Unit, Medical School, University of La Laguna, 38071 La Laguna, Tenerife, Spain. Email: rborges{at}ull.es

Chromogranins (Cgs) are the major soluble proteins of dense-core secretory vesicles. Chromaffin cells from Chga null mice [chromogranin A knock-out (CgA-KO)] exhibited 30% reduction in the content and in the release of catecholamines compared with wild type. This was because of a lower secretion per single exocytotic event, rather than to a lower frequency of exocytotic events. Cell incubation with L-DOPA produced an increase in the vesicular amine content of wild-type, but not CgA-KO vesicles. In contrast, intracellular electrochemistry showed that L-DOPA produced a significantly larger increase in cytosolic amines in CgA-KO cells than in the wild type. These data indicate that the mechanisms for vesicular accumulation in CgA-KO cells were fully saturated. Patch-amperometry recordings showed a delayed initiation of the amperometric signal after vesicle fusion, whereas no changes were observed in vesicle size or fusion pore kinetics despite the smaller amine content. We conclude that intravesicular proteins are highly efficient systems directly implicated in transmitter accumulation and in the control of neurosecretion.

Key words: amperometry; catecholamines; fusion pore; neurosecretion; patch amperometry; secretory vesicle

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Received Nov. 29, 2007; revised Jan. 15, 2008; accepted Feb. 7, 2008.

Correspondence should be addressed to Dr. Ricardo Borges, Pharmacology Unit, Medical School, University of La Laguna, 38071 La Laguna, Tenerife, Spain. Email: rborges{at}ull.es

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