Large conductance calcium-voltage operated potassium channels as novel regulators of inflammatory and acute nociception in rat.

Thomas Scullion, Sharron Dolan. Glasgow Caledonian University, Glasgow, UK

Large conductance calcium-voltage operated potassium (BKca) channels are a diverse ion channel family that modulate many cellular processes, mainly serving as regulators of Ca2+ entry mediated processes such as neurotransmission and exocytosis1. The pore forming α-subunit is coded for by the single gene KCNMA1, which undergoes extensive alternative splicing, imparting differential properties to the overall channel kinetics. One such splice variant, STREX (STRess axis regulated EXon), greatly enhances channel Ca2+ sensitivity thus increasing channel excitability and consequently heightening the overall cell excitability2. Aberrant changes in spinal cord BKca channel levels are now thought to contribute to the development of pathological pain3. This study investigated the effects of pharmacological modulation of spinal BKca channel activity on pain processing, and expression of spinal cord BKca channels in response to carrageenan-induced inflammation.

Spinal cord tissues were collected from normal untreated adult male Wistar rats (n=6) and rats injected intradermally into the left hindpaw with carrageenan (3%; 50 μl) or saline (50 μl) (n=6/group). Expression of BKca channel splice variants ZERO and STREX mRNA were analysed using real-time PCR analysis. Animals were anaesthetized with isoflurane (2%) carried in O2 via a nose cone and the effect(s) of intrathecally administered BKca channel agonist NS 1619 (10-20 μg) or drug-vehicle (saline/20% DMSO) on responses to noxious thermal and mechanical stimulation of the hindpaw were assessed in adult male Wistar rats (n=6/group) before and after intradermal hindpaw injection of carrageenan (3%; 50 μl). The effect of intrathecal administration of NS 1619 on acute nociception was also assessed in untreated animals (n=6/group). Data were analysed using an ANOVA with post-hoc Tukey’s test.

Real-time PCR revealed that BKca channel and both splice variants ZERO and STREX mRNA are constitutively expressed in spinal cord. STREX mRNA expression showed a significant 2.1 fold increase in spinal cord 6 hours post-carrageenan (p < 0.05 vs. control). In vivo behavioural studies showed that in normal rats NS1619 (10μg) induced short lasting analgesia (p < 0.05 vs. drug-vehicle). NS 1619 had no effect on thermal or mechanical hyperalgesia induced by carrageenan.

The results suggest that an up-regulation in STREX expression in spinal cord may contribute to plasticity-related changes in nociceptive processing in response to inflammation, by inducing heightened neuronal excitation. Furthermore these data show that NS 1619 has conditional analgesic properties shown only in the acute nociceptive scenario suggesting that central BKca channels may underlie the regulation of acute pain processing pathways. Therefore BKca channels may prove to be a novel therapeutic target in the development of future analgesics.

References

1. Chen, L., L. Tian, et al. (2005). J Biol Chem 280(39): 33599-33609.

2. Chen, S. R., Y. Q. Cai, et al. (2009). J Neurochem 110(1): 352-362.

3. Cui, J., H. Yang, et al. (2009). Cell Mol Life Sci 66(5): 852-875.