Carbon monoxide inhibits capacitative calcium entry in human platelets.
The cytosolic calcium concentration in human platelets is elevated by several agonists via receptor-operated mechanisms involving both Ca(2+) release from intracellular stores and Ca(2+) entry. In order to get a mechanistic insight in the effect of carbon monoxide (CO)-containing solutions, this work examines the changes in [Ca(2+)](i) induced by 100 microM adenosine 5'diphosphate (ADP), 0.1 IU/ ml thrombin, 0.5 microM thapsigargin or 0.5 microM ionomycin in human platelets. In a saline solution bubbled with CO, the increase of [Ca(2+)](i) produced by thrombin was 72+/-4% of the response evoked in the control solution (CO-free) and the response elicited by ADP was 64+/-8% of the control. When a mixture of 5% CO/95% N(2) was used, the responses were 70+/-7% of control for thrombin and 79+/-6% of control for ADP. The mobilization of stored calcium produced by thrombin in a calcium-free solution and the increase of [Ca(2+)](i) produced by subsequent introduction of 1 mM extracellular calcium were both reduced in the presence of CO (82+/-6% and 78+/-5% of control, respectively). Similar reductions in the presence of CO were found when platelets were stimulated by ADP (62+/-8% and 60+/-8% for mobilization in calcium-free media and calcium entry, respectively). Although the change in [Ca(2+)](i) induced by ionomycin in the presence of extracellular calcium was almost the same in the absence or presence of CO (97+/-5% of control), the entry induced by depletion of reservoirs with the ionophore undergoes a significant reduction in a solution bubbled with CO (84+/-5% of control). In agreement with the concept that CO has a direct inhibitory effect on capacitative calcium entry, a reduction to 47+/-6% of control was obtained when sarco/endoplasmic reticulum ATPase was blocked by thapsigargin. Diverse mechanisms could be responsible for the effect of CO on calcium entry. On the one hand, a decrease in the calcium release from intracellular stores or an increase in the rate of its back-sequestration could occur, being the reduction of capacitative calcium entry an indirect consequence of a diminished emptying of reservoirs. On the other hand, CO could have a direct inhibitory effect on the pathway that produces the calcium entry. The decrease in the Ca(2+) signal in the presence of CO evoked by receptor-independent emptying of reservoirs indicates that a direct effect of CO on capacitative calcium entry participates in the antiaggregatory properties of CO. The proposal that CO inhibits directly store-operated calcium influx widens the potential mechanisms by which heme oxygenase regulates cell functions.
Centro de Investigaciones Cardiovasculares, Catedra de Fisiologia con Biofisica, Facultad de Ciencias Médicas, Universidad Nacional de La Plata 60 y 120, 1900 La Plata, Argentina. ogende@atlas.med.unlp.edu.ar
Oscar A
OA
Gende
D000244:Adenosine Diphosphate / Q000494:pharmacology*; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002245:Carbon Dioxide / Q000494:pharmacology*; D002478:Cells, Cultured; D006801:Humans; D015759:Ionomycin / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D019284:Thapsigargin / Q000494:pharmacology*; D013917:Thrombin / Q000494:pharmacology*
D002245:Carbon Dioxide; D015759:Ionomycin; D000244:Adenosine Diphosphate; D019284:Thapsigargin; D013917:Thrombin; D002118:Calcium