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.
Gende
Oscar A
OA
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
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