Dynamic regulation of intracellular Ca²⁺ concentration in arotic endothelial cells

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.