Ca2+ accumulation into acidic organelles mediated by Ca2+- and vacuolar H+-ATPases in human platelets.
Most physiological agonists increase cytosolic free [Ca2+]c (cytosolic free Ca2+ concentration) to regulate a variety of cellular processes. How different stimuli evoke distinct spatiotemporal Ca2+ responses remains unclear, and the presence of separate intracellular Ca2+ stores might be of great functional relevance. Ca2+ accumulation into intracellular compartments mainly depends on the activity of Ca2+- and H+-ATPases. Platelets present two separate Ca2+ stores differentiated by the distinct sensitivity to thapsigargin and TBHQ [2,5-di-(t-butyl)-1,4-hydroquinone]. Although one store has long been identified as the dense tubular system, the nature of the TBHQ-sensitive store remains uncertain. Treatment of platelets with GPN (glycylphenylalanine-2-naphthylamide) impaired Ca2+ release by TBHQ and reduced that evoked by thrombin. In contrast, GPN did not modify Ca2+ mobilization stimulated by ADP or AVP ([arginine]vasopressin). Treatment with nigericin, a proton carrier, and bafilomycin A1, an inhibitor of the vacuolar H+-ATPase, to dissipate the proton gradient into acidic organelles induces a transient increase in [Ca2+]c that was abolished by previous treatment with the SERCA (sarcoplasmic/endoplasmic-reticulum Ca2+-ATPase) 3 inhibitor TBHQ. Depleted acidic stores after nigericin or bafilomycin A1 were refilled by SERCA 3. Thrombin, but not ADP or AVP, reduces the rise in [Ca2+]c evoked by nigericin and bafilomycin A1. Our results indicate that the TBHQ-sensitive store in human platelets is an acidic organelle whose Ca2+ accumulation is regulated by both Ca2+- and vacuolar H+-ATPases.
López
José J
JJ
Department of Physiology, University of Extremadura, 10071 Cáceres, Spain.
Camello-Almaraz
Cristina
C
Pariente
José A
JA
Salido
Ginés M
GM
Rosado
Juan A
JA
D000244:Adenosine Diphosphate / Q000502:physiology; D001127:Arginine Vasopressin / Q000494:pharmacology; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002478:Cells, Cultured; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006873:Hydroquinones / Q000494:pharmacology; D018942:Macrolides / Q000494:pharmacology; D015388:Organelles / Q000737:chemistry / Q000502:physiology; D013917:Thrombin / Q000494:pharmacology; D025262:Vacuolar Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D006873:Hydroquinones; D018942:Macrolides; D001127:Arginine Vasopressin; D000244:Adenosine Diphosphate; C040929:bafilomycin A1; C018855:2-tert-butylhydroquinone; D013917:Thrombin; D025262:Vacuolar Proton-Translocating ATPases; D000252:Calcium-Transporting ATPases; D002118:Calcium