Korean J Physiol Pharmacol.  2012 Feb;16(1):37-42. 10.4196/kjpp.2012.16.1.37.

A Novel Pathway Underlying the Inhibitory Effects of Melatonin on Isolated Rat Urinary Bladder Contraction

• Han JH
• Chang IH
• Myung SC
• Lee MY
• Kim WY
• Lee SY
• Lee SY
• Lee SW
• Kim KD

• KMID: 2285438
• DOI: http://doi.org/10.4196/kjpp.2012.16.1.37

Abstract

The aim of the present study was to elucidate the direct effects of melatonin on bladder activity and to determine the mechanisms responsible for the detrusor activity of melatonin in the isolated rat bladder. We evaluated the effects of melatonin on the contractions induced by phenylephrine (PE), acetylcholine (ACh), bethanechol (BCh), KCl, and electrical field stimulation (EFS) in 20 detrusor smooth muscle samples from Sprague-Dawley rats. To determine the mechanisms underlying the inhibitory responses to melatonin, melatonin-pretreated muscle strips were exposed to a calcium channel antagonist (verapamil), three potassium channel blockers [tetraethyl ammonium (TEA), 4-aminopyridine (4-AP), and glibenclamide], a direct voltage-dependent calcium channel opener (Bay K 8644), and a specific calcium/calmodulin-dependent kinase II (CaMKII) inhibitor (KN-93). Melatonin pretreatment (10(-8)~10(-6) M) decreased the contractile responses induced by PE (10(-9)~10(-4) M) and Ach (10(-9)~10(-4) M) in a dose-dependent manner. Melatonin (10(-7) M) also blocked contraction induced by high KCl ([KCl]ECF; 35 mM, 70 mM, 105 mM, and 140 mM) and EFS. Melatonin (10(-7) M) potentiated the relaxation response of the strips by verapamil, but other potassium channel blockers did not change melatonin activity. Melatonin pretreatment significantly decreased contractile responses induced by Bay K 8644 (10(-11)~10(-7) M). KN-93 enhanced melatonin-induced relaxation. The present results suggest that melatonin can inhibit bladder smooth muscle contraction through a voltage-dependent, calcium-antagonistic mechanism and through the inhibition of the calmodulin/CaMKII system.

Keyword

Melatonin; Urinary bladder; Smooth muscles; Overactive bladder; Nocturia

MeSH Terms

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester
4-Aminopyridine
Acetylcholine
Animals
Benzylamines
Bethanechol
Calcium Channels
Contracts
Melatonin
Muscle, Smooth
Muscles
Nocturia
Phenylephrine
Phosphotransferases
Potassium Channel Blockers
Quaternary Ammonium Compounds
Rats
Rats, Sprague-Dawley
Relaxation
Sulfonamides
Urinary Bladder
Urinary Bladder, Overactive
Verapamil
3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester
4-Aminopyridine
Acetylcholine
Benzylamines
Bethanechol
Calcium Channels
Melatonin
Phenylephrine
Phosphotransferases
Potassium Channel Blockers
Quaternary Ammonium Compounds
Sulfonamides
Verapamil

Figure

• 

  Fig. 1 Effects of melatonin pretreatment (10-8~10-6 M) on the concentration-response curve for phenylephrine (109~10-4 M) and acetylcholine (10-9~10-4 M) in Sprague-Dawley rat detrusor smooth muscles. (A) Pretreatment with melatonin dose-dependently decreased the contractile responses induced by phenylnephrine (n=8 in each). (B) Melatonin blocked acetylcholine-induced contractions, which were stronger than phenylnephrine contractions (n=12 in each). Asterisk means p<0.05. Each point represents the mean±standard error of means (SEM); if the SEMs were not shown, the bars fall within the size of the symbols.

• 

  Fig. 2 Effects of melatonin pretreatment (10-8~10-6 M) on the concentration-response curve for bethanechol (10-9~10-4 M) and effects of 10-7 M melatonin pretreatment on the KCl-induced contractions ([KCl]ECF ; 35 mM, 70 mM, 105 mM and 140 mM) in Sprague-Dawley rat detrusor smooth muscles. (A) Melatonin blocked bethanechol-induced contractions, which were stronger than phenylnephrine contractions, but contraction inhibition effects of the melatonin were not reversed by luzindazole (a melatonin receptor antagonist) (n=12 in each). (B) The melatonin inhibited the contractions at all four conditions of high extracellular KCl concentrations (n=8 in each). Asterisk means p<0.05. Each point represents the mean±standard error of means (SEM).

• 

  Fig. 3 Effects of 10-7 M melatonin pretreatment on the frequency-response curve for electrical field stimulation (EFS, 1~40 Hz) and effects of 10-7 M melatonin pretreatment on the concentration-response curve for verapamil relaxation (10-9~10-4 M) in Sprague-Dawley rat detrussor muscles. (A) The melatonin significantly inhibited the EFS-induced contractions (n=8 in each). (B) The basal tension of each strip was adjusted to the optimal isometric tension at which contraction with phenylephrine 10-5 M was maximal. The curve was slightly but significantly inhibited by melatonin pretreatment (n=8 in each). Asterisk means p<0.05. Each point represents the mean±standard error of means (SEM) of the results.

• 

  Fig. 4 Effects of 10-7 M melatonin pretreatment on the concentration-response curve for Bay K 8644 contraction (10-11~10-7 M) in Sprague-Dawley rat detrussor muscles and in the absence or the presence of melatonin (10-7 M) alone or combination with KN-93 (a specific calcium/calmodulin-dependent kinase II inhibitor: 10-6 M), the differences of KCl (35 mM)-induced contraction were evaluated. (A) The contractile responses of Bay K 8644 were almost completely inhibited by melatonin (n=6 in each). (B) KN-93 at 10-6 M concentration enhanced the melatonin-induced inhibiting effects of the KCl-induced contraction (n=12 in each). Asterisk means p<0.05. Each point represents the mean±standard error of means (SEM) of the results.

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