title: Acidic NAADP-releasable Ca(2+) compartments in the megakaryoblastic cell line MEG01.
abstract: BACKGROUND
  A novel family of intracellular Ca(2+)-release channels termed two-pore channels (TPCs) has been presented as the receptors of NAADP (nicotinic acid adenine dinucleotide phosphate), the most potent Ca(2+) mobilizing intracellular messenger. TPCs have been shown to be exclusively localized to the endolysosomal system mediating NAADP-evoked Ca(2+) release from the acidic compartments.
  
  
  OBJECTIVE
  The present study is aimed to investigate NAADP-mediated Ca(2+) release from intracellular stores in the megakaryoblastic cell line MEG01.
  
  
  METHODS
  Changes in cytosolic and intraluminal free Ca(2+) concentrations were registered by fluorimetry using fura-2 and fura-ff, respectively; TPC expression was detected by PCR.
  
  
  RESULTS
  Treatment of MEG01 cells with the H(+)/K(+) ionophore nigericin or the V-type H(+)-ATPase selective inhibitor bafilomycin A1 revealed the presence of acidic Ca(2+) stores in these cells, sensitive to the SERCA inhibitor 2,5-di-(tert-butyl)-1,4-hydroquinone (TBHQ). NAADP releases Ca(2+) from acidic lysosomal-like Ca(2+) stores in MEG01 cells probably mediated by the activation of TPC1 and TPC2 as demonstrated by TPC1 and TPC2 expression silencing and overexpression. Ca(2+) efflux from the acidic lysosomal-like Ca(2+) stores or the endoplasmic reticulum (ER) results in ryanodine-sensitive activation of Ca(2+)-induced Ca(2+) release (CICR) from the complementary Ca(2+) compartment.
  
  
  CONCLUSIONS
  Our results show for the first time NAADP-evoked Ca(2+) release from acidic compartments through the activation of TPC1 and TPC2, and CICR, in a megakaryoblastic cell line.
authors: Department of Physiology (Cellular Physiology Research Group), University of Extremadura, Cáceres, Spain.
authors: Natalia
authors: N
authors: Dionisio
authors: Letizia
authors: L
authors: Albarrán
authors: José J
authors: JJ
authors: López
authors: Alejandro
authors: A
authors: Berna-Erro
authors: Ginés M
authors: GM
authors: Salido
authors: Régis
authors: R
authors: Bobe
authors: Juan A
authors: JA
authors: Rosado