Calcium efflux from platelet vesicles of the dense tubular system. Analysis of the possible contribution of the Ca2+ pump

• Published in: Molecular and cellular biochemistry 1999-09, Vol.199 (1-2), p.7-14
• Main Authors: Teijeiro, R G, Sotelo Silveira, J R, Sotelo, J R, Benech, J C
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - metabolism; ATP; Blood Platelets - drug effects; Blood Platelets - metabolism; Calcimycin - pharmacology; Calcium; Calcium - metabolism; Calcium Signaling - drug effects; Calcium-Transporting ATPases - drug effects; Calcium-Transporting ATPases - metabolism; Enzyme Inhibitors - pharmacology; Humans; In Vitro Techniques; Ionomycin - pharmacology; Ionophores - pharmacology; Isoenzymes - drug effects; Isoenzymes - metabolism; Phosphates - metabolism; Propranolol - pharmacology; Ruthenium; Ruthenium Red - pharmacology; Spermidine - pharmacology; Thapsigargin - pharmacology; Trifluoperazine - pharmacology
• ISSN: 0300-8177; 1573-4919
• DOI: 10.1023/A:1006928110564

The ATP dependent Ca2+ uptake of platelet vesicles was inhibited by the two hydrophobic drugs trifluoperazine (TFP) and propranolol (PROP). Inhibition was significantly lowered when Pi was used instead of oxalate as a precipitant agent. When the ATPase ligands substrate (Mg2+ and Pi) were absent of the efflux medium, a slow release of Ca2+ which did not couple with ATP synthesis (passive Ca2+ efflux) was observed. Both, TFP and PROP enhanced the passive Ca2+ efflux. This enhanced efflux was partially inhibited only when Mg2+ and Pi were added together to the efflux reaction media, but it was not affected by spermidine, ruthenium red or thapsigargin (TG). The Ca2+ ionophores A23187 and ionomycin, also enhanced passive Ca2+ efflux. However, in this case, Ca2+ efflux was inhibited just by inclusion of Mg2+ to the medium. Ca2+ efflux promoted by Triton X-100 was not affected by either Mg2+ or Pi, included together or separately into the efflux medium. The ATP Pi measured in the presence of Triton X-100 and millimolar Ca2+ concentrations was inhibited by both TFP and PROP, but not by Ca2+ ionophores up to 4 microM. The data suggest that the observed enhancement of passive Ca2+ efflux promoted by TFP and PROP could be attributed to a direct effect of these drugs over the platelet Ca2+ pump isoforms (Sarco Endoplasmic Reticulum Calcium ATPase, SERCA2b and SERCA3) themselves, as it was reported for the sarcoplasmic reticulum Ca2+ ATPase (SERCA1).