Calcium efflux from platelet vesicles of the dense tubular system. Analysis of the possible contribution of the Ca2+ pump.
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).
Teijeiro
R G
RG
División Biofísica, Instituto de Investigaciones Biológicas Clemente Estable, Montevideo, Uruguay.
Sotelo Silveira
J R
JR
Sotelo
J R
JR
Benech
J C
JC
D000255:Adenosine Triphosphate / Q000378:metabolism; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D000252:Calcium-Transporting ATPases / Q000187:drug effects* / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D007527:Isoenzymes / Q000187:drug effects / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism; D011433:Propranolol / Q000494:pharmacology*; D012430:Ruthenium Red / Q000494:pharmacology; D013095:Spermidine / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D014268:Trifluoperazine / Q000494:pharmacology*
D004791:Enzyme Inhibitors; D007476:Ionophores; D007527:Isoenzymes; D010710:Phosphates; D012430:Ruthenium Red; D014268:Trifluoperazine; D000001:Calcimycin; D015759:Ionomycin; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D011433:Propranolol; D000252:Calcium-Transporting ATPases; D002118:Calcium; D013095:Spermidine