J Basic Clin Physiol Pharmacol 2017; 28(4): 371–375 Saravanakumar Snekalatha* and Praghalathan Kanthakumar a Ascorbic acid does not modulate potassium currents in cultured human lymphocytes DOI 10.1515/jbcpp-2016-0182 Received December 1, 2016; accepted January 13, 2017; previously published online March 17, 2017 Abstract Background: Ascorbic acid (AA) is known to modulate lymphocyte function, but the mechanism of action is not clearly understood. As voltage-gated potassium cur- rents play an important role in lymphocyte function, the effect of AA on voltage-gated potassium currents was studied. Methods: Peripheral blood mononuclear cells were cul- tured in the presence of increasing concentrations of AA (0, 0.125, 0.25, 0.5, and 1 mM). Potassium currents in resting lymphocytes were studied by whole cell patch clamp technique using a depolarizing protocol. Lympho- cyte function was assessed by measuring interleukin-2 (IL-2) secretion after mitogenic stimulation by ELISA. Results: The mean current density of potassium currents recorded from cells cultured for 48 h in the presence of 0.125 mM AA was not significantly different from that of cells cultured in the absence of AA. There was about 50% inhibition of IL-2 secretion in cell cultures with 0.125 mM AA when compared to controls without AA. At higher concentrations of AA, the IL-2 secretion decreased further. Conclusions: The results of the study indicate that the inhibition of lymphocyte function by AA in vitro may not be due to inhibition of potassium currents in the concen- tration tested. Keywords: culture; interleukin-2; patch clamp; potassium channels. Introduction Vitamin C [ascorbic acid (AA)] is known to have beneficial effects on health including anticarcinogenic effect and immune-enhancing activity. Many clinical trials have investigated the effect of vitamin C and its effectiveness in preventing infections like common cold. While some of the studies did show a positive effect of vitamin C in prevent- ing and treating infections, others did not show a similar effect. Similarly, studies done to demonstrate the effect of AA on T lymphocyte function are not conclusive. Vitamin C supplementation was found to have positive effects on lymphocyte function [1], but studies in which vitamin C was added to in vitro cell cultures report a decrease in T cell function. Addition of vitamin C to T cell cultures in high concentrations decreased viability and decreased the production of cytokines in response to stimulation by PMA/ionomycin [2]. The mechanism of action of AA in immune cells is not clear. AA was found to alter the expression of many proteins in T cells in a time- and dose-dependent manner. The expression of phosphatidyl inositol transfer protein was found to increase, while the expression of potassium channels decreased in a time-dependent manner [3]. In another study, supplementation of vitamin C for 5 weeks caused an increase in the phosphatidyl inositol transfer protein expression but did not produce any change in the apoptosis of peripheral blood mononuclear cells and plasma potassium levels [4]. Modulation of expression of ion channels is one of the mechanisms by which an immunomodulant could exert its effect. Immunosuppressant dexamethasone decreased the expression of Kv1.3 channels, while lipopolysaccha- ride increased the channel expression in macrophages cultured in the presence of these drugs for 24 h [5]. Treat- ment of Jurkat T lymphocytes with dexamethasone for 2 h caused significant decrease in voltage-gated potassium currents and calcium entry in these cells [6]. Modula- tion of channel function in immune cells by drugs could have potential therapeutic applications in the treatment of infections, autoimmune diseases, and cancer. In the present work, the effect of AA on voltage-gated potassium currents in lymphocytes was studied by adding supra- physiological concentrations of AA to these cell cultures. a Present address: Department of Physiology, Otago School of Medical Sciences, University of Otago, Dunedin, New Zealand *Corresponding author: Saravanakumar Snekalatha, Department of Physiology, ESIC Medical College and PGIMSR, K.K. Nagar, Chennai - 600078, India, Phone: 044-24748959, E-mail: sneka_r@yahoo.co.in Praghalathan Kanthakumar: Department of Physiology, Christian Medical College, Vellore, India