Validation of a method to measure the uptake of [3H]dopamine by human platelets

Phorbol esters increase [(3)h]-dopamine uptake by human platelets

Dopamine is taken up by platelets by an energy and temperature dependent process that does not involve a known dopamine receptor. Whilst dopamine uptake by platelets has been shown to be altered in several disease states, little is known about factors controlling dopamine uptake by platelets which could cause such changes. As phorbol esters have been shown to affect dopamine functions in other tissues we examined the effect of phorbol esters on dopamine uptake by human platelets. Phorbol 12,13-dibutyrate increased [(3)H]-dopamine uptake by platelets in a dose dependent manner. Similarly, phorbol 12,13-didecanoate increased [(3)H-dopamine uptake by platelets but 4α phorbol 12,13-didecanoate, which does not affect protein kinase, did not. Staurosporin, a protein kinase inhibitor, reversed the effect of phorbol 12,13-dibutyrate. These data suggest protein kinases can modulate dopamine uptake by platelets.

[3H]dopamine uptake by platelet storage granules in schizophrenia

[3H]Dopamine (DA) uptake by platelet storage granules was determined in 26 schizophrenic male patients, paranoid type (14 acute stage; 12 in remission) and 20 age-matched, normal controls. Maximum velocity (Vmax) of DA uptake was significantly higher in acute patients, than patients in remission or controls (p less than 0.05). The apparent Michaelis constant (Km) of DA uptake in acute patients was also significantly different from chronic patients (p less than 0.05). Preincubation with reserpine (10(-4), 10(-5) M) produced a substantial diminution of DA uptake, while haloperidol (10(-4), 10(-5) M) did not affect the assay. Considering that a DA dysequilibrium in schizophrenia may be expressed not only in the brain, but also in the periphery and that an increased amount of DA accumulated in the vesicles, implies that an increased quantity of catecholamine is available for release, our findings suggest additional evidence for the role of DA overactivity in the pathophysiology of this disorder.

Dopamine uptake by platelets from subjects with schizophrenia: a correlation with the delusional state of the patient

The uptake of 3H-dopamine by platelets from patients with a number of psychiatric disorders has been compared with that by platelets from normal volunteers. Overall, 3H-dopamine uptake by platelet-rich plasma (PRP) from 25 schizophrenic subjects did not differ from 3H-dopamine uptake by PRP from 22 nonschizophrenic patients and 61 normal volunteers. In the schizophrenic group, however, there was an increased spread of results with seven values falling outside the range of results observed in the control group. Furthermore, of the patients rated, only for the schizophrenic patients was there an inverse correlation between 3H-dopamine uptake by platelets and the rating for delusions on the Scale for the Assessment of Positive Symptoms. Thus, 3H-dopamine uptake by platelet seems, in some way, to be linked to be delusional state of the patient. Further study of 3H-dopamine uptake by platelets is warranted in a larger and more diverse group of patients to determine the significance of altered dopamine uptake by platelets from some schizophrenic subjects and the correlation between platelet 3H-dopamine uptake and the delusional state of these subjects.

An assay to measure the simultaneous uptake of [3H]dopamine and [14C]serotonin by the human platelet reveals an imipramine-insensitive [3H]dopamine uptake mechanism

To determine whether a specific dopamine uptake mechanism is present on the human platelet the simultaneous uptake of [3H]dopamine and [14C]serotonin by platelets was measured. Utilising a dual radiolabel uptake technique, platelets have been shown to take up serotonin more rapidly and to a greater extent than they take up dopamine. Furthermore, at high concentrations serotonin was able to reduce dopamine uptake by platelets by 60% whereas dopamine had no effect on serotonin uptake. Similarly, imipramine and reserpine reduced (97% and 74% respectively) serotonin uptake by platelets in a dose-dependent manner, but did not affect the uptake of dopamine. Our data show that platelets take up dopamine by a mechanism independent of the imipramine-sensitive serotonin uptake mechanism. Furthermore, the increased capacity of platelets to store serotonin is because serotonin, unlike dopamine, is transported into the dense granules of the platelet.