J Vet Sci.  2010 Jun;11(2):103-106. 10.4142/jvs.2010.11.2.103.

Role of PKG-L-type calcium channels in the antinociceptive effect of intrathecal sildenafil

• Kim WM
• Yoon MH
• Cui JH

• KMID: 1110855
• DOI: http://doi.org/10.4142/jvs.2010.11.2.103

Abstract

Sildenafil increases the cyclic guanosine monophosphate (cGMP) by inhibition of a phosphodiesterase 5, thereby leading to an antinociceptive effect. The increased cGMP may exert the effect on an L-type calcium channel through the activation of protein kinase G (PKG). The purpose of this study was to examine the possible involvement of a PKG-L-type calcium channel on the effect of sildenafil at the spinal level. Catheters were inserted into the intrathecal space of male SD rats. Pain was induced by applying 50 microliter of a 5% formalin solution to the hindpaw. The sildenafil-induced effect was examined after an intrathecal pretreatment of a PKG inhibitor (KT 5823), or a L-type calcium channel activator (FPL 64176). Intrathecal sildenafil produced an antinociceptive effect during phase 1 (0~10 min interval) and phase 2 (10~60 min interval) in the formalin test. Intrathecal KT 5823 and FPL 64176 attenuated the antinociceptive effect of sildenafil during both phases. Sildenafil is effective against both acute pain and the facilitated pain state at the spinal level. In addition, the inhibition of an L-type calcium channel by activation of the PKG may contribute to the antinocieptive mechanism of sildenafil in the spinal cord.

Keyword

formalin test; L-type calcium channel; PKG; sildenafil; spinal cord

MeSH Terms

Animals
Calcium Channel Agonists/pharmacology
Calcium Channels, L-Type/*physiology
Carbazoles/pharmacology
Cyclic GMP-Dependent Protein Kinases/antagonists & inhibitors/*physiology
Dose-Response Relationship, Drug
Male
Pain/drug therapy/*physiopathology
Pain Measurement
Piperazines/*pharmacology/therapeutic use
Protein Kinase Inhibitors/pharmacology
Purines/pharmacology/therapeutic use
Pyrroles/pharmacology
Rats
Rats, Sprague-Dawley
Sulfones/*pharmacology/therapeutic use

Figure

• 

  Fig. 1 Dose response curves of intrathecal sildenafil on the flinching response during phase 1 (A) and phase 2 (B) in the formalin test. Sildenafil was administered 10 min before the formalin injection. Data are presented as the sum of flinches in each phase. Sildenafil dose-dependently suppressed the flinches during both phases. Each line represents mean ± SE of 6~8 rats. Compared with control, *p < 0.05, †p < 0.01, ‡p < 0.001.

• 

  Fig. 2 The effects of intrathecal KT 5823 (0.02 nmol/L) and FPL 64176 (0.9 nmol/L) on the antinociception effect produced by intrathecal sildenafil (45 nmol/L) during phase 1 (A) and phase 2 (B) in the formalin test. KT 5823 and FPL 64176 were administered 10 min before the delivery of sildenafil, and then the formalin test was done 10 min later. KT 5823 and FPL 64176 reversed the effect of sildenafil during both phases. Data are presented as the sum of flinches in each phase. Each bar represents mean ± SE of 5~6 rats. Compared with sildenafil, *p < 0.05, †p < 0.01.

Reference

1. Araiza-Saldaña CI, Reyes-García G, Bermúdez-Ocaña DY, Pérez-Severiano F, Granados-Soto V. Effect of diabetes on the mechanisms of intrathecal antinociception of sildenafil in rats. Eur J Pharmacol. 2005. 527:60–70.

2. Beavo JA. Cyclic nucleotide phosphodiesterases: functional implications of multiple isoforms. Physiol Rev. 1995. 75:725–748.

3. Beavo JA, Reifsnyder DH. Primary sequence of cyclic nucleotide phosphodiesterase isozymes and the design of selective inhibitors. Trends Pharmacol Sci. 1990. 11:150–155.

4. Boolell M, Gepi-Attee S, Gingell JC, Allen MJ. Sildenafil, a novel effective oral therapy for male erectile dysfunction. Br J Urol. 1996. 78:257–261.

5. Bowersox SS, Gadbois T, Singh T, Pettus M, Wang YX, Luther RR. Selective N-type neuronal voltage-sensitive calcium channel blocker, SNX-111, produces spinal antinociception in rat models of acute, persistent and neuropathic pain. J Pharmacol Exp Ther. 1996. 279:1243–1249.

6. Coderre TJ, Melzack R. The role of NMDA receptor-operated calcium channels in persistent nociception after formalin-induced tissue injury. J Neurosci. 1992. 12:3671–3675.

7. de Vente J, Markerink-van Ittersum M, Vles JS. The role of phosphodiesterase isoforms 2, 5, and 9 in the regulation of NO-dependent and NO-independent cGMP production in the rat cervical spinal cord. J Chem Neuroanat. 2006. 31:275–303.

8. Fukuizumi T, Ohkubo T, Kitamura K. Spinally delivered N-, P/Q- and L-type Ca2+-channel blockers potentiate morphine analgesia in mice. Life Sci. 2003. 73:2873–2881.

9. Galeotti N, Bartolini A, Ghelardini C. Role of intracellular calcium in acute thermal pain perception. Neuropharmacology. 2004. 47:935–944.

10. Gibson A. Phosphodiesterase 5 inhibitors and nitrergic transmission-from zaprinast to sildenafil. Eur J Pharmacol. 2001. 411:1–10.

11. Hara K, Saito Y, Kirihara Y, Sakura S, Kosaka Y. Antinociceptive effects of intrathecal L-type calcium channel blockers on visceral and somatic stimuli in the rat. Anesth Analg. 1998. 87:382–387.

12. Miller RJ. Multiple calcium channels and neuronal function. Science. 1987. 235:46–52.

13. Mixcoatl-Zecuatl T, Aguirre-Bañuelos P, Granados-Soto V. Sildenafil produces antinociception and increases morphine antinociception in the formalin test. Eur J Pharmacol. 2000. 400:81–87.

14. Pyne NJ, Arshavsky V, Lochhead A. cGMP signal termination. Biochem Soc Trans. 1996. 24:1019–1022.

15. Salom JB, Castelló-Ruiz M, Burguete MC, Guzmán C, Jover-Mengual T, Torregrosa G, Jover R, Lizasoain I, Alborch E. Role of K+ and Ca2+ fluxes in the cerebroarterial vasoactive effects of sildenafil. Eur J Pharmacol. 2008. 581:138–147.

16. Sousa AM, Prado WA. The dual effect of a nitric oxide donor in nociception. Brain Res. 2001. 897:9–19.

17. Ückert S, Hedlund P, Andersson KE, Truss MC, Jonas U, Stief CG. Update on phosphodiesterase (PDE) isoenzymes as pharmacologic targets in urology: present and future. Eur Urol. 2006. 50:1194–1207.

18. Wang X, Robinson PJ. Cyclic GMP-dependent protein kinase and cellular signaling in the nervous system. J Neurochem. 1997. 68:443–456.

19. Westenbroek RE, Hoskins L, Catterall WA. Localization of Ca2+ channel subtypes on rat spinal motor neurons, interneurons, and nerve terminals. J Neurosci. 1998. 18:6319–6330.

20. Yaksh TL, Rudy TA. Chronic catheterization of the spinal subarachnoid space. Physiol Behav. 1976. 17:1031–1036.

21. Yoon MH, Kim WM, Lee HG, Kim YO, Huang LJ, An TH. Roles of opioid receptor subtypes on the antinociceptive effect of intrathecal sildenafil in the formalin test of rats. Neurosci Lett. 2008. 441:125–128.

22. Yoshimura N, Seki S, de Groat WC. Nitric oxide modulates Ca2+ channels in dorsal root ganglion neurons innervating rat urinary bladder. J Neurophysiol. 2001. 86:304–311.