Boron-Doped Diamond Microelectrodes Reveal Reduced Serotonin Uptake Rates in Lymphocytes from Adult Rhesus Monkeys Carrying the Short Allele of the 5-HTTLPR

Abstract

Uptake resolved by high-speed chronoamperometry on a second-by-second basis has revealed important differences in brain serotonin transporter function associated with genetic variability. Here, we use chronoamperometry to investigate variations in serotonin transport in primary lymphocytes associated with the rhesus serotonin transporter gene-linked polymorphism (rh5-HTTLPR), a promoter polymorphism whose orthologs occur only in higher order primates including humans. Serotonin clearance by lymphocytes is Na+-dependent and inhibited by the serotonin-selective reuptake inhibitor paroxetine (Paxil®), indicative of active uptake by serotonin transporters. Moreover, reductions in serotonin uptake rates are evident in lymphocytes from monkeys with one or two copies of the short ‘s’ allele of the rh5-HTTLPR (s/s<s/l<l/l). These findings illustrate that rh5-HTTLPR-related alterations in serotonin uptake are present during adulthood in peripheral blood cells natively expressing serotonin transporters. Moreover, they suggest that lymphocytes can be used as peripheral biomarkers for investigating genetic or pharmacologic alterations in serotonin transporter function. Use of boron-doped diamond microelectrodes for measuring serotonin uptake, in contrast to carbon fiber microelectrodes used previously in the brain, enabled these high-sensitivity and high-resolution measurements. Boron-doped diamond microelectrodes show excellent signal-to-noise and signal-to-background ratios due mainly to low background currents and are highly resistant to fouling when exposed to lymphocytes or high concentrations of serotonin.

Serotonin Uptake Is Largely Mediated by Platelets versus Lymphocytes in Peripheral Blood Cells

“…Others and we have previously reported that lymphocytes and lymphoblastoid cell lines express functional SERT. 23,24,41,21,51 However, the chronoamperometry and flow cytometry results presented here are not in strong agreement with prior findings. It is possible that lymphocytes express SERT but that, in nonactivated or nonmalignant cells, surface SERT localization is absent or present only in very low amounts.…”

“…Serotonin transporter regulation and function have been studied using radiometric assay, voltammetry, or fluorescence microscopy in synaptosomes, 16−18 platelets, 19,20 peripheral blood cells (PBCs), 21,22 lymphoblasts, 23−25 brain slices, 1 and the intact brains of experimental animals. [26][27][28]2 Although SERT function can be effectively measured by all of these methods, ambiguity arises when samples containing multiple cell types, such as PBCs, are investigated due to the difficulty in assigning uptake to individual cell types.…”

“…Serotonin transporters are reported to be expressed in primary B-lymphocytes, 41 T-lymphocytes, 41 and mixed lymphocyte populations. 44,41,45,46,21 However, others have failed to detect (or have detected only small amounts of) SERT in B-lymphocytes 33,34 and T-lymphocytes. 30 Human lymphoblastoid cell lines, which are Epstein−Barr virusimmortalized B-lymphocytes, are also thought to express functional SERT and have been used to study human SERT gene variants.…”

Molecular Functionalization of Graphite Surfaces: Basal Plane versus Step Edge Electrochemical Activity

“…[1][2][3][4] Glassy carbon (GC), boron doped diamond and graphite have long received attention for electroanalytical and electrocatalytic measurements, [5][6][7][8][9][10][11] and, more recently, carbon nanotubes and graphene have generated considerable interest. [12][13][14][15][16][17] However, despite well-defined bulk properties and structure, carbon materials can possess rather complex surface chemistry that may substantially impact the resulting electrochemistry.…”

The Use of Conducting Diamond in Electrochemistry

“…A variety of insulating films have been employed, such as glass, epoxy, polyimide, nail polish, polypropylene tubing, and electrophoretic paint, however, to date the problem has still not been reliably solved. Such electrodes are currently finding use for in vivo [57] and in vitro neurotransmitter, antioxidant, and pH measurements associated with a range of different medical research areas, such as irritable bowel syndrome [58], cancer [59], stomach disorders [60], and genetic variability [61].…”