57 Figure 2. Graphic representation of the three major learn more intracellular pathways, the cAMP system, the IP3-DAG system, and the arachidonic acid system. G0 and G5, G-protein receptors; IP3-DAG, inositol 1,4,5-triphosphate-diacylglycerol; PKC protein kinase C; PLA, phospholipase … In conclusion,
this hypothesis combines special potential factors of vulnerability in bipolar patients, such as altered Na/K ATPase Inhibitors,research,lifescience,medical and adenylyl cyclase activity (probably on a genetic basis), widi the multiplying effects of increased intracellular calcium mobilization or calcium influx into the cell. Potentially beneficial effects of anticonvulsants through interference with intracellular calcium signaling are reported at various cellular levels. A decreased Na/K ATPase activity has been described as a state marker in acutely ill bipolar patients, as it is not seen in healthy relatives.58 Besides lithium, CBZ is also capable of stimulating Na/K ATPase, measured as rubidium Inhibitors,research,lifescience,medical 86 uptake into synaptosomes59 causing a reduction in
intracellular calcium. Like lithium, CBZ also reduces the activity of protein kinase A and C by reducing cAMP-dependent Inhibitors,research,lifescience,medical protein phosphorylation. This also, in turn, reduces the gene expression of proteins responsible for neurotransmission.60 However, anticonvulsants may also affect voltage-dependent calcium channels directly. CBZ exerts strong calcium channel antagonism in vitro, synergistic
Inhibitors,research,lifescience,medical with verapamil, thus making an action on L-type calcium channels likely.61 Similar findings are also true for VPA, which seems to exert calcium-antagonistic effects through blockade of another voltage-dependent calcium channel, the T channel.62 The two new antiepileptic drugs gabapentin and Lf G also exert calcium-antagonistic effects.63-67 It has to be said, however, that in another study both CBZ and VPA, in therapeutic concentrations, appeared not to affect calcium currents in neocortical Inhibitors,research,lifescience,medical neurons in vitro.68 Thus, a special aberration Adenosine of intracellular calcium regulation, as assumed for bipolar patients, may be a prerequisite for the calcium-antagonistic action of these antiepileptic drugs in man. In addition, other actions on ionic currents that may be especially important for suppression of seizures by CBZ, VPA, and LTG include inhibition of voltage-dependent sodium channels,69, 70 and an increase in an early transient potassium outward current.71 – 73 Table I (page 29) summarizes the modes of action on the synaptic and cytoplasmic levels of some anticonvulsants commonly used as mood stabilizers. Table I. Anticonvulsants used as mood stabilizers and their proposed mode of action.