ns-309 and Pain

N-methyl-D-aspartate receptor (NMDAR) antagonists have been shown to reduce mechanical hypersensitivity in animal models of inflammatory pain. However, their clinical use is associated with significant dose-limiting side effects. Small-conductance Ca-activated K channels (SK) have been shown to modulate NMDAR activity in the brain. We demonstrate that in vivo activation of SK channels in the spinal cord can alleviate mechanical hypersensitivity in a rat model of inflammatory pain. Intrathecal (i.t.) administration of the SK channel activator, 6,7-dichloro-1H-indole-2,3-dione 3-oxime (NS309), attenuates complete Freund adjuvant (CFA)-induced mechanical hypersensitivity in a dose-dependent manner. Postsynaptic expression of the SK channel subunit, SK3, and apamin-sensitive SK channel-mediated currents recorded from superficial laminae are significantly reduced in the dorsal horn (DH) after CFA. Complete Freund adjuvant-induced decrease in SK-mediated currents can be reversed in vitro by bath application of NS309. In addition, immunostaining for the SK3 subunit indicates that SK3-containing channels within DH neurons can have both somatic and dendritic localization. Double immunostaining shows coexpression of SK3 and NMDAR subunit, NR1, compatible with functional interaction. Moreover, we demonstrate that i.t. coadministration of NS309 with an NMDAR antagonist reduces the dose of NMDAR antagonist, DL-2-amino-5-phosphonopentanoic acid (DL-AP5), required to produce antinociceptive effects in the CFA model. This reduction could attenuate the unwanted side effects associated with NMDAR antagonists, giving this combination potential clinical implications.

Topics: Animals; Disease Models, Animal; Freund's Adjuvant; Indoles; Inflammation; Injections, Spinal; Male; Oximes; Pain; Pain Threshold; Posterior Horn Cells; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Small-Conductance Calcium-Activated Potassium Channels; Spinal Cord; Treatment Outcome

Small-conductance Ca(2+)-activated potassium (SK) channels constitute a family of ion channels that are regulated by the cytosolic Ca(2+) concentration. Increases in the intracellular Ca(2+) concentration ([Ca(2+)](i)) result in opening of the channels, which in turn will lead to changes in the membrane potential. As the name implies, the channels are of small conductance, but even so, they are known to play a crucial role in several physiological processes, such as modulation of neurotransmitter and hormone secretion, as well as memory and learning (e.g.,see Curr Med Chem 14:1437-1457, 2007). Owing to the central role of SK channels, they have attracted much attention as potential drug targets, both with respect to identification of activators and blockers of SK channel activity for indications such as, e.g., epilepsy, pain, and urinary incontinence (see Curr Med Chem 14:1437-1457, 2007; Curr Pharm Des 12:397-406, 2006). Thus, great efforts have been put into the development of robust high-throughput assays for detection and characterization of modulators of SK channel activity. In the present chapter, we describe two fluorescence-based Tl(+)influx assays for detection of positive and negative SK channel modulators.

Topics: Benzofurans; Cell Culture Techniques; Cell Line; Epilepsy; Ethers, Cyclic; Humans; Indoles; Ion Channel Gating; Kidney; Membrane Potentials; Oximes; Pain; Small-Conductance Calcium-Activated Potassium Channels; Thallium; Urinary Incontinence