Effects of dextroamphetamine, lithium chloride, sodium valproate and carbamazepine on intraplatelet Ca2+ levels.
OBJECTIVE
To explore the possible involvement of second-messenger pathways in the pathophysiology of bipolar disorder and the mechanism of action of mood stabilizers, we investigated the effects of dextroamphetamine (a model for mania) and the most widely used mood stabilizers, lithium chloride, sodium valproate and carbamazepine, on intraplatelet levels of calcium ion ([Ca2+).


METHODS
In the first part of the study, dextroamphetamine was administered in vivo in a double-blind, placebo-controlled, crossover design. In the second part of the study, platelets from untreated subjects were incubated in vitro with dextroamphetamine, lithium chloride, sodium valproate or carbamazepine.


METHODS
Fifteen healthy men between 18 and 45 years of age.


METHODS
Basal, thrombin-induced and serotonin- (5-HT) induced intraplatelet [Ca2+] determined by means of fura-2 fluorescent intensity.


RESULTS
In vivo administration of dextroamphetamine had no effect on basal or agonist-induced intraplatelet [Ca2+]. However, in vitro basal platelet [Ca2+] was significantly higher in samples incubated with dextroamphetamine (86.8 nmol/L [standard error of the mean, SEM, 3.9], p < 0.001), lithium chloride (76.4 nmol/L [SEM 3.1], p < 0.002), sodium valproate (82.7 nmol/L [SEM 3.7], p < 0.001) and carbamazepine (84.8 nmol/L [SEM 3.3], p < 0.001) than in the controls (58.2 nmol/L [SEM 2.3]). Thrombin-induced and 5-HT-induced peak cytosolic [Ca2+] were significantly greater than control levels in samples incubated with carbamazepine (277.1 nmol/L [SEM 19.9] v. 195.8 nmol/L [SEM 12.2], p < 0.002; and 153.0 nmol/L [SEM 8.2] v. 115.4 nmol/L [SEM 5.7], p < 0.003, respectively).


CONCLUSIONS
This study does not support the involvement of intraplatelet [Ca2+] in the dextroamphetamine model of mania; however, the modulation of intraplatelet [Ca2+] by the mood stabilizers lithium chloride, sodium valproate and carbamazepine implicates intracellular [Ca2+] in the therapeutic mechanisms of these drugs and the pathophysiological basis of mania.
Ulrich
Michele L
ML
Department of Psychiatry, Walter Mackenzie Health Sciences Centre, University of Alberta, Edmonton, Alta.
Rotzinger
Susan
S
Asghar
Sheila J
SJ
Jurasz
Paul
P
Tanay
Veronique A
VA
Dunn
Susan M J
SM
Radomski
Marek
M
Greenshaw
Andy
A
Silverstone
Peter H
PH
D000293:Adolescent; D000328:Adult; D014150:Antipsychotic Agents / Q000494:pharmacology*; D001792:Blood Platelets / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects*; D002220:Carbamazepine / Q000494:pharmacology*; D003913:Dextroamphetamine / Q000494:pharmacology*; D005260:Female; D006801:Humans; D018021:Lithium Chloride / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged; D013917:Thrombin / Q000378:metabolism; D014635:Valproic Acid / Q000494:pharmacology*
D014150:Antipsychotic Agents; D015220:Calcium Channels; D002220:Carbamazepine; D014635:Valproic Acid; D013917:Thrombin; D018021:Lithium Chloride; D003913:Dextroamphetamine