Dynamics of calcium fluxes in human platelets assessed in calcium-free medium

Dynamics of changes in cytosolic calcium concentration resulting from facilitation of calcium leakage from the stores and (or) blocking the pathways of its reuptake back into the stores or extrusion out of the cell (or both) have been investigated experimentally. It has been found that: (a) no mechanisms other than the membrane leakage, PMCA or SERCA, are involved in the discharge of calcium stores and calcium extrusion or reuptake; (b) the discharge of calcium stores in the absence of both its extrusion and reuptake back into the stores depends only on membrane leakage, the asymptotic calcium concentration in cytosol depending only on the initial content of the stores and being independent of the leakage; (c) the dynamics of the activity of both PMCA and SERCA depend on the initial rate of calcium influx, the dynamics differing from each other at high initial rates of calcium influx; (d) whereas there is no observable background activity of PMCA, background activity of SERCA is observed.