Voltage-dependent biphasic effects of chloroquine on delayed rectifier K+-channel currents in murine thymocytes

Abstract

Lymphocytes are of rich in delayed rectifier K(+)-channels (Kv1.3) in their plasma membranes, and the channels play crucial roles in the lymphocyte activation and proliferation. Since chloroquine, a widely used anti-malarial drug, exerts immunosuppressive effects, it will affect the channel currents in lymphocytes. In the present study, employing the standard patch-clamp whole-cell recording technique, we examined the effects of chloroquine on the channels expressed in murine thymocytes. Published papers report that chloroquine will inhibit voltage-dependent K(+)-channel currents by plugging into the open-pore. We observed, indeed, that chloroquine suppressed the pulse-end currents of Kv1.3-channels at higher voltage steps. Surprisingly, however, we found that the drug enhanced the peak currents at both higher and lower voltage steps. Since chloroquine showed such biphasic effects on the thymocyte K(+)-channels, and since those effects were voltage dependent, we examined the effects of chloroquine on the activation and the inactivation of the channel currents. We noted that chloroquine shifted both the activation and the inactivation curves toward the hyperpolarizing potential, and that those shifts were more emphasized at lower voltage steps. We conclude that chloroquine facilitates both the activation and the inactivation of Kv1.3-channel currents in thymocytes, and that those effects are voltage dependent.

Salicylate Inhibits Thrombopoiesis in Rat Megakaryocytes by Changing the Membrane Micro-Architecture

“…5). As previously demonstrated in murine megakaryocytes or thymocytes [20,36], 100 nM margatoxin almost totally abolished the Kv1.3-channel currents in rat megakaryocytes (Fig. 5A).…”

“…4Ba). This represented a "C-type inactivation" pattern in kinetic studies [42], suggesting that salicylate induced a conformational collapse of the selectivity filter (inactivation gates) within a pore-forming domain of the K + -channel [20]. Since salicylate is amphiphilic [15], it tends to accumulate between the lipid bilayers of the plasma membrane after its penetration [43].…”

“…(Osaka, Japan), and margatoxin, from Peptide Institute (Osaka, Japan), were separately dissolved in the external solution at a final concentrations of 3 mM and 100 nM. We delivered the reagents to the cells by the standing hydrostatic pressure of 3 cmH 2 O from a nearby pipette as described previously [2,19,20]. Then, whole-cell membrane currents were recorded before and after 1 min exposure to the drug and after a 2 min washout.…”

Olopatadine Inhibits Exocytosis in Rat Peritoneal Mast Cells by Counteracting Membrane Surface Deformation

“…In megakaryocytes or thymus lymphocytes, microscopic changes in the cell surface area were induced by membrane invagination during thrombopoiesis [26] or by the accumulation of lipophilic drugs into the lipid bilayers [27]. In our previous studies, such microscopic changes in these cells were most precisely monitored by measurement of the whole-cell membrane capacitance (Cm) [16,28,29,30,31].…”

Benidipine Suppresses in situ Proliferation of Leukocytes and Slows the Progression of Renal Fibrosis in Rat Kidneys with Advanced Chronic Renal Failure

“…From our results, blocking the Kv1.3 channels overexpressed in leukocytes by benidipine was also useful for the treatment of renal fibrosis in advanced CRF. In addition to DHP CCBs, including benidipine and nifedipine [13], we recently demonstrated in a series of in vitro studies that antibiotics, such as clarithromycin and chloroquine, exerted inhibitory effects on Kv1.3 channel currents in lymphocytes [35,36]. The likely neuromuscular side effects of the channel inhibition include epileptic seizures or enteric twitches since it blocks the synaptic channels in both the central and enteric nervous systems [37,38].…”