Kv7 Channel Activation Inhibits Prostaglandin E2 Induced Detrusor Overactivity in Mouse Isolated Bladder

Francesca Caputo2, Peter Sidaway1, Keith Brain1. 1University of Birmingham, Birmingham, West Midlands, UK, 2University of Siena, Siena, Ital.

Production of prostanoids, specifically prostaglandin E2 (PGE2) is associated with bladder pathologies including bladder overactivity that follows spinal cord injury (Masunaga et al. 2006), and bladder outlet obstruction (Schroder et al. 2004). In vitro, PGE2 induces spontaneous contractions in the isolated mouse bladder, although the effects upon electrical field stimulation (EFS) evoked contractions remain unclear (Kobayter et al. 2012).

Bladders were isolated from male Balb/c mice, 8-12 weeks of age (procedures carried out in accordance with the European Communities Council Directives (86/609/EEC of 24/11/86). Bladders were dissected into 4 strips and placed into a modular contraction assay bath under 1g of tension, and perfused with oxygenated Krebs solution. PGE2 (50 μM) facilitated EFS-induced bladder smooth muscle contractions (10 Hz 10 pulses, 0.5 ms pulse width, 50 V stimulations) (control: 6.8±1.2 mN vs PGE2: 9.0±1.5 mN, paired t-test, P < 0.05 np = 8, n = 4). Pretreatment with flupirtine, a Kv7 channel activator, reduced the PGE2-induced augmentation of contraction; this effect was particularly evident following short impulse stimulus trains (2 impulses at 10Hz reduced from 125±24% to 67±20%; across all stimulus train durations [2, 5, 10 and 20 pulses], n = 4, p< 0.05 vs controls, two way ANOVA). Control contractions were unaffected by flupirtine alone. The effects of flupirtine were unaffected by P2X1 receptor inhibition (α,β-meATP, 10 μM), but were sensitive to muscarinic receptor inhibition (atropine 1 μM), suggesting that flupirtine is able to inhibit the effects of PGE2 via interaction with the cholinergic system.

In conclusion, flupirtine, a clinically available Kv7 channel activator, modestly inhibits the potentiating effects of PGE2 upon EFS induced bladder smooth muscle contraction, whilst leaving control contractions unaffected. These data suggest that at least some of the effects of PGE2 on EFS evoked contractions are due to closure of Kv7 channels, and that the principal interaction is with the cholinergic signalling pathway.

Kobayter S, Young JS, Brain KL. 2012. Prostaglandin E2 induces spontaneous rhythmic activity in mouse urinary bladder independently of efferent nerves. Br J Pharmacol 165:401-13.

Masunaga K, Yoshida M, Inadome A, Iwashita H, Miyamae K, Ueda S. 2006. Prostaglandin E2 release from isolated bladder strips in rats with spinal cord injury. Int J Urol 13:271-276.

Schroder A, Newgreen D, Andersson KE. 2004. Detrusor responses to prostaglandin E2 and bladder outlet obstruction in wild-type and EP1 receptor knockout mice. J Urol 172:1166-1170.