Chemical and enzymatic modification of the platelet binding site for two antidepressant drugs

Inhibition of platelet serotonin uptake by cytochrome P450 inhibitors miconazole and econazole

Serotonin uptake in human platelets was inhibited by cytochrome P450 inhibitors such as miconazole and econazole but not clotrimazole. There was a correlation between inhibition of serotonin uptake and inhibition of imipramine binding, suggesting that these P450 inhibitors may inhibit serotonin uptake via direct binding to the transporter. P450 inhibitor effects on serotonin uptake did not seem to be related to the effects of these compounds on intracellular calcium mobilization. Additionally, nitric oxide pathway stimulation does not appear to be involved.

Kinase inhibitors compete with imipramine for binding and inhibition of serotonin transport

Effects of kinase inhibitors and activators on the binding of tritiated imipramine and inhibition of serotonin uptake were tested in platelets. The majority of compounds inhibited specific [3H]imipramine binding and serotonin uptake with affinities similar to those reported for their action on protein kinases themselves. Many of these compounds are derivatives with modified naphthalenesulfonamide or isoquinolinesulfonamide structures, which appear to compete directly with imipramine for binding to the serotonin transporter. This is of great importance for studies involving kinase regulation since at these concentrations, the inhibitors and activators were previously thought to interact virtually exclusively with protein kinases.

Interaction of lectins with human platelet serotonin transporter

Lectin affinity chromatography was used to demonstrate the glycoprotein nature of the serotonin (5-HT) transporter. The human platelet transporter protein was solubilized with 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), labelled with [3H]cyanoimipramine and chromatographed on lectin columns. Wheat germ, gorse seed and lentil lectin-agarose columns specifically retained 5-HT transporter. Peanut and horse gram lectins were ineffective. Concanavalin A showed high non-specific adsorption. Binding of [3H]imipramine to platelet membranes or solubilized 5-HT transporter was not affected by lectins. These data suggest that the lectin interaction with 5-HT transporter is extrinsic to the antidepressant binding site.