Serotonin transport and storage in rabbit blood platelets—The effects of reserpine and imipramine

Serotonin transport and storage in suspensions of washed rabbit platelets were investigated by following the exchange of platelet-bound [³H]serotonin and [¹⁴C]serotonin added to the suspending medium. Assuming a three-compartment system (suspending medium, platelet cytoplasm and platelet storage organelles), the transfer rates between the different compartments were calculated from the exchange data by statistical analysis. Reserpine reduced the storage organelle serotonin content by inhibiting the transfer of serotonin from the cytoplasm into the amine storage organelles. It also reduced the fraction of serotonin in the cytoplasm transferred per unit of time into the suspending medium. Imipramine (20 μM) inhibited the uptake of serotonin across the platelet plasma membrane into the cytoplasm and reduced the fraction of cytoplasmic serotonin transferred per unit of time into the suspending medium. At this concentration it had no effect on serotonin transport across the amine storage organelle membrane in either direction. The method used allows the serotonin transfer rates across the platelet plasma membrane to be distinguished from those across the amine storage organelle membrane in intact cells, and permits these transfer rates to be estimated simultaneously. The method may be used for determining the effects of drugs that interfere with transport and storage of biogenic amines and in defining the defects in diseases with abnormal transport or storage of biogenic amines.