Are dopamine receptors present on human lymphocytes?

Abstract

Abstract The characteristics of [3H]spiperone binding to human lymphocytes have been examined. The haloperidol displaceable component of [3H]spiperone binding to human lymphocytes was not saturable, and stereoselective displacement by the isomers of butaclamol was not observed. There was no correlation between the ability of known dopamine active drugs to cause displacement of the ligand and their rank order of potency. Chloroquine, a drug with no dopaminergic action, was the most potent displacing agent examined. Fragmentation of the cells caused a marked decrease in the haloperidol displaceable component of [3H]spiperone binding, and saturable binding to the lymphocyte membrane fragments was not observed. Lysis of cells after equilibrium incubation with [3H]spiperone caused a marked reduction in the haloperidol displaceable component of ligand binding. Association of [3H]spiperone with lymphocytes was unaffected by the metabolic inhibitor iodoacetate, or by replacement of sodium ions by lithium ions in the incubation medium, suggesting that such association did not involve an active uptake process. We cannot confirm the existence of dopamine receptors on the surface of human lymphocytes. We suggest that the apparent association of [3H]spiperone with lymphocytes is due to some passive uptake process causing accumulation of the ligand within the cells.