Calcium stores, SERCAs and PMCA in human platelets stimulated by thrombin: A reinterpretation

It has been found on the basis of experimental data by Redondo and co-workers (Cell. Signal. 2008) that under the conditions of the experiments thrombinstimulated discharge of DTS is negligible compared to that of the acidic stores. There is good reason to believe that SERCA is activated by unbinding calcium ion(s) from the binding site(s) located on the inner (stores-facing) side of the (macro)molecule. Serious errors in the quoted paper are pointed out: 1) The fundamental difference between calcium quantity or concentration (essentially non-temporal value) and its fluxes (essentially temporal values) has been ignored throughout. 2) Calcium extrusion by PMCA has not been taken into account when analyzing thrombin-stimulated increase in cytosolic calcium concentration. 3) Use of integration to evaluate calcium entry or its amount in the stores is erroneous. 4) A single graph in each figure of the quoted paper (Figs. 1F – 4F) presented to characterize Ca 2+ remaining in the stores (nM.s) cannot reflect calcium content in the stores of both types, their properties being different.