Two distinct Ca2+ compartments show differential sensitivity to thrombin, ADP and vasopressin in human platelets.
Recent studies propose the existence of two distinct Ca2+ compartments in human platelets based on the expression of different SERCA isoforms with distinct sensitivity to thapsigargin and 2,5-di-(tert-butyl)-1,4-hydroquinone (TBHQ). Using fura-2-loaded human platelets we have found that depletion of the TBHQ sensitive store reduces thrombin--but not ADP--or vasopressin (AVP)-induced Ca2+ release. Redistribution of cytosolic Ca2+ after thrombin stimulation resulted in overloading of the TBHQ-sensitive store. This phenomenon was not observed with ADP or AVP. We found that NAADP decreases the Ca2+ concentration into the stores in permeabilized platelets, which is prevented by depletion of the TBHQ-sensitive store. Nimodipine, an inhibitor of the NAADP receptor, reduced thrombin-induced Ca2+ release from the TBHQ-sensitive stores, without having any effect on the responses elicited by ADP or AVP. Finally, the phospholipase C inhibitor, U-73122, abolished ADP- and AVP-induced Ca2+ release, suggesting that their responses are entirely dependent on IP3 generation. In contrast, treatment with both U-73122 and nimodipine was required to abolish thrombin-induced Ca2+ release. We suggest that thrombin evokes Ca2+ release from TBHQ-sensitive and insensitive stores, which requires both NAADP and IP3, respectively, while ADP and AVP exert an IP3-dependent release of Ca2+ from the TBHQ-insensitive compartment in human platelets.
López
Jose J
JJ
Department of Physiology, University of Extremadura, Av. Universidad s/n, Cáceres 10071, Spain.
Redondo
Pedro C
PC
Salido
Ginés M
GM
Pariente
Jose A
JA
Rosado
Juan A
JA
D000244:Adenosine Diphosphate / Q000494:pharmacology*; D001792:Blood Platelets / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000502:physiology; D002451:Cell Compartmentation; D004963:Estrenes / Q000494:pharmacology; D006801:Humans; D006873:Hydroquinones / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007527:Isoenzymes; D009249:NADP / Q000031:analogs & derivatives / Q000494:pharmacology; D009553:Nimodipine / Q000494:pharmacology; D011760:Pyrrolidinones / Q000494:pharmacology; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019284:Thapsigargin / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology*; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors; D014667:Vasopressins / Q000494:pharmacology*
D002121:Calcium Channel Blockers; D004963:Estrenes; D006873:Hydroquinones; D007527:Isoenzymes; D011760:Pyrrolidinones; D014667:Vasopressins; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D009249:NADP; C024376:NAADP; D009553:Nimodipine; D000244:Adenosine Diphosphate; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; C018855:2-tert-butylhydroquinone; D010738:Type C Phospholipases; D013917:Thrombin; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D002118:Calcium