Differential effect of halothane and forskolin on platelet cytosolic Ca2+ mobilization and aggregation.
BACKGROUND
Previous works have suggested that the impairment of platelet aggregation by halothane was partly related to a stimulation of cyclic adenosine monophosphate (cAMP) production, to an inhibitory effect on Ca2+ signaling, or both. Intracellular Ca2+ measurements therefore were undertaken, first to determine the critical steps in the platelet CaZ+ signaling cascade most likely to be affected by halothane or by an increase in cAMP production, and second to establish if the effect of halothane involves aggregation-related biochemical pathways triggered by an increase in internal Ca2+.


METHODS
Human washed platelets were treated with halothane or forskolin for 5 min before application of either platelet-activating factor, thrombin, U46619, or thapsigargin. The cytosolic Ca2+ concentration ([Ca2+]i) was measured with the fluorescent Ca2+ indicator fura-2. Nephelometric measurements were also performed to assay the aggregation process.


RESULTS
Our results indicate that pretreating platelets with halothane leads to a partial impairment of the [Ca2+]i increase induced either by U46619, thrombin, or platelet-activating factor, but this had no significant effect on the [Ca2+]i response triggered by thapsigargin. In addition, our results show that halothane inhibits platelet aggregation triggered by U46619, but not by thapsigargin. Conversely, forskolin completely inhibited the [Ca2+]i response to U46619 and thapsigargin and prevented platelet aggregation induced by both agonists.


CONCLUSIONS
These results suggest that halothane and cAMP exert their effects on platelet aggregation and Ca2+ signaling through different mechanisms, and that halothane cannot impair platelet aggregation independently of phospholipase C stimulation.
Département de Physiologie, Université de Montréal, Québec, Canada.
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Corbin
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Blaise
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D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000097:blood*; D005576:Colforsin / Q000494:pharmacology*; D006221:Halothane / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D013050:Spectrometry, Fluorescence; D010738:Type C Phospholipases / Q000378:metabolism
D018685:Anesthetics, Inhalation; D010975:Platelet Aggregation Inhibitors; D005576:Colforsin; D010738:Type C Phospholipases; D002118:Calcium; D006221:Halothane