title: Chromogranin B gene ablation reduces the catecholamine cargo and decelerates exocytosis in chromaffin secretory vesicles.
abstract: 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 (approximately 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.
authors.affiliation: Unit of Pharmacology, Medical School, La Laguna University, 38071 La Laguna, Tenerife, Spain.
authors.forename: Jésica
authors.initials: J
authors.lastname: Díaz-Vera
authors.forename: Yézer G
authors.initials: YG
authors.lastname: Morales
authors.forename: Juan R
authors.initials: JR
authors.lastname: Hernández-Fernaud
authors.forename: Marcial
authors.initials: M
authors.lastname: Camacho
authors.forename: Mónica S
authors.initials: MS
authors.lastname: Montesinos
authors.forename: Federico
authors.initials: F
authors.lastname: Calegari
authors.forename: Wieland B
authors.initials: WB
authors.lastname: Huttner
authors.forename: Ricardo
authors.initials: R
authors.lastname: Borges
authors.forename: José D
authors.initials: JD
authors.lastname: Machado
mesh_terms: D000311:Adrenal Glands / Q000166:cytology; D000818:Animals; D002395:Catecholamines / Q000378:metabolism*; D019439:Chromaffin Cells / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure*; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D053378:Chromogranin B / Q000172:deficiency*; D015259:Dopamine Agents / Q000494:pharmacology; D004563:Electrochemistry / Q000379:methods; D015180:Electrophoresis, Gel, Two-Dimensional / Q000379:methods; D005089:Exocytosis / Q000187:drug effects / Q000235:genetics*; D007980:Levodopa / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D022142:Secretory Vesicles / Q000187:drug effects / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods
chemical_list: D002395:Catecholamines; D053378:Chromogranin B; D015259:Dopamine Agents; D007980:Levodopa