Irreversible ATP Depletion Caused by Low Concentrations of Formaldehyde and of Calcium-chelator Esters in Intact Human Red Cells

Calcium chelators which can be incorporated inside small cells without disruption have become useful tools to investigate the role of intracellular ionized calcium in the processes of cell activation and signal-effect mediation. In experiments designed to investigate further Ca2+ pump function in chelator-loaded human red cells we found that the chelator-loading procedure itself caused delayed Ca2+-pump inhibition when pump function was explored by increasing the intracellular Ca2+ levels with the aid of the divalent cation ionophore A23187. Ca2+-pump inhibition was found to be secondary to ATP-depletion, and ATP-depletion, in turn, could be attributed to formaldehyde, which was released during the hydrolytic incorporation of free chelator, from the cleavage of the four ester groups which anchor it to cell membranes on addition to cell suspensions. The evidence suggests that the formaldehyde released stays largely within the cells. Formaldehyde, in concentrations of up to 20 mmol/l cells had no direct effects on Ca2+ transport in red cells, other than through ATP depletion. Procedures to circumvent the difficulties arising from the formaldehyde effects are outlined and discussed.