DYNAMIC REGULATION OF INTRACELLULAR CA2-CELLS( CONCENTRATION IN AORTIC ENDOTHELIAL)

In non-excitable cells, a Ca2+ entry pathway is opened after the deple tion of intracellular Ca2+ store sites. We have tried to estimate the sensitivity of this pathway to Ca2+ release using bovine aortic endoth elial cells. Single application of a high concentration (30 mu M) of A TP 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+ st ore site was reloaded to 97.1% of its initial filling state. When thap sigargin was applied to this cell in Mn2+ solution, Mn2+-induced quenc hing of fura-2 dye started when 19.3 +/- 5.3% of Ca2+ release, produce d by 30 nM ATP, had occurred. Therefore, Ca2+ release required for Mn2 + entry was estimated as 11.1 +/- 3.0% of stored Ca2+. These results i ndicate that intracellular Ca2+ concentration is controlled dynamicall y by simultaneously occurring Ca2+ release and entry in bovine aortic endothelial cells.