In non-excitable cells, a Ca2+ entry pathway is opened after the depletion of intracellular Ca2+ store sites. We have tried to estimate ATP released almost all stored Ca2+ in Ca2+-free extracellular solution, whereas a low concentration of ATP (30 nM) produced a partial (57.3 ± 3.0%) release of Ca2+. By 10 min of Ca2+ re-perfusion, the Ca2+ store site was reloaded to 97.1% of its initial filling state. When thapsigargin was applied to this cell in Mn2+ solution, Mn2+-induced quenching of fura-2 dye started when 19.3 ± 5.3% of Ca2+ release, produced by 30 nM ATP, had occurred. Therefore, Ca2+ release required for Mn2+ entry was estimated as 11.1 C 3.0% of stored Ca2+. These results indicate that intracellular Ca2+ concentration is controlled dynamically by simultaneously occurring Ca2+ release and entry in bovine aortic endothelial cells.
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