title: Ouabain enhances exocytosis through the regulation of calcium handling by the endoplasmic reticulum of chromaffin cells.
abstract: The augmentation of neurotransmitter and hormone release produced by ouabain inhibition of plasmalemmal Na+/K+-ATPase (NKA) is well established. However, the mechanism underlying this action is still controversial. Here we have shown that in bovine adrenal chromaffin cells ouabain diminished the mobility of chromaffin vesicles, an indication of greater number of docked vesicles at subplasmalemmal exocytotic sites. On the other hand, ouabain augmented the number of vesicles undergoing exocytosis in response to a K+ pulse, rather than the quantal size of single vesicles. Furthermore, ouabain produced a tiny and slow Ca2+ release from the endoplasmic reticulum (ER) and gradually augmented the transient elevations of the cytosolic Ca2+ concentrations ([Ca2+]c) triggered by K+ pulses. These effects were paralleled by gradual increments of the transient catecholamine release responses triggered by sequential K+ pulses applied to chromaffin cell populations treated with ouabain. Both, the increases of K+-elicited [Ca2+]c and secretion in ouabain-treated cells were blocked by thapsigargin (THAPSI), 2-aminoethoxydiphenyl borate (2-APB) and caffeine. These results are compatible with the view that ouabain may enhance the ER Ca2+ load and facilitate the Ca2+-induced-Ca2+ release (CICR) component of the [Ca2+]c signal generated during K+ depolarisation. This could explain the potentiating effects of ouabain on exocytosis.
authors: Instituto Teófilo Hernando, Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, and Servicio de Farmacología Clínica, Instituto de Investigación Sanitaria, Hospital Universitario de la Princesa, Madrid, Spain.
authors: Juan
authors: J
authors: Milla
authors: Mónica S
authors: MS
authors: Montesinos
authors: Jose David
authors: JD
authors: Machado
authors: Ricardo
authors: R
authors: Borges
authors: Elba
authors: E
authors: Alonso
authors: Ana J
authors: AJ
authors: Moreno-Ortega
authors: María F
authors: MF
authors: Cano-Abad
authors: Antonio G
authors: AG
authors: García
authors: Ana
authors: A
authors: Ruiz-Nuño
mesh_terms: D000311:Adrenal Glands / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D000818:Animals; D001896:Boron Compounds / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism; D002417:Cattle; D019439:Chromaffin Cells / Q000187:drug effects* / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects; D004721:Endoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects*; D010042:Ouabain / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D022142:Secretory Vesicles / Q000187:drug effects / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology
chemical_list: D001896:Boron Compounds; D002395:Catecholamines; D004791:Enzyme Inhibitors; D002110:Caffeine; D010042:Ouabain; D019284:Thapsigargin; C109986:2-aminoethoxydiphenyl borate; D011188:Potassium; D002118:Calcium