Adrenergic receptor subtypes in human peripheral blood lymphocytes.

Ricci et al1 reported that human peripheral blood lymphocytes express α1-adrenergic receptor subtypes. The authors present results of radioligand binding assays with [3H]-prazosin as the radioligand for α1-adrenergic receptors, showing that the maximal density of the binding sites is 175 fmol per 106 cells. This would mean that the actual number of receptors per cell would be exactly 100 000, which is an unusually high number of receptors. Cell lines that are known for their high expression of α1-adrenergic receptors have been reported to express 10 000 to 25 000 receptors per cell.2 3 We have to keep in mind, however, that these numbers are found on kidney or smooth muscle cells, which are much larger than the freshly isolated lymphocytes that were used in the study by Ricci. Moreover, it is known for other G-protein–coupled receptors, eg, β2-adrenergic receptors, that are expressed on lymphocytes that the actual number of receptors per cell is around 2000.4 Thus, the number reported by Ricci et al for α1-adrenergic receptors on lymphocytes is extraordinary high.