Menthol inhibits detrusor contractility independently of TRPM8 activation.
Agonists such as icilin and menthol can activate the cool temperature-sensitive ion channel TRPM8. However, biological responses to menthol may occur independently of TRPM8 activation. In the rodent urinary bladder, menthol facilitates the micturition reflex but inhibits muscarinic contractions of the detrusor smooth muscle. The site(s) of TRPM8 expression in the bladder are controversial. In this study we investigated the regulation of bladder contractility in vitro by menthol. Bladder strips from wild type and TRPM8 knockout male mice (25-30 g) were dissected free and mounted in organ baths. Isometric contractions to carbachol (1 nM-30 µM), CaCl2 (1 µM to 100 mM) and electrical field stimulation (EFS; 8, 16, 32 Hz) were measured. Strips from both groups contracted similarly in response to both carbachol and EFS. Menthol (300 µM) or nifedipine (1 µM) inhibited carbachol and EFS-induced contractions in both wild type and TRPM8 knockout bladder strips. Incubation with the sodium channel blocker tetrodotoxin (1 µM), replacement of extracellular sodium with the impermeant cation N-Methyl-D-Glucamine, incubation with a cocktail of potassium channel inhibitors (100 nM charybdotoxin, 1 µM apamin, 10 µM glibenclamide and 1 µM tetraethylammonium) or removal of the urothelium did not affect the inhibitory actions of menthol. Contraction to CaCl2 was markedly inhibited by either menthol or nifedipine. In cultured bladder smooth muscle cells, menthol or nifedipine abrogated the carbachol or KCl-induced increases in [Ca2+]i. Intravesical administration of menthol increased voiding frequency while decreasing peak voiding pressure. We conclude that menthol inhibits muscarinic bladder contractions through blockade of L-type calcium channels, independently of TRPM8 activation.
Department of Pharmacology, University of Campinas (UNICAMP), Campinas, Brazil.
Antonio Celso Saragossa
AC
Ramos-Filho
Wolfson Centre for Age-Related Diseases, King's College London, London, United Kingdom.
Ajay
A
Shah
Department of Anatomy, Cellular Biology, Physiology and Biophysics, Institute of Biology, University of Campinas (UNICAMP), Campinas, Brazil.
Taize Machado
TM
Augusto
Department of Anatomy, Cellular Biology, Physiology and Biophysics, Institute of Biology, University of Campinas (UNICAMP), Campinas, Brazil.
Guilherme Oliveira
GO
Barbosa
Department of Pharmacology, University of Campinas (UNICAMP), Campinas, Brazil.
Luiz Osorio
LO
Leiria
Department of Anatomy, Cellular Biology, Physiology and Biophysics, Institute of Biology, University of Campinas (UNICAMP), Campinas, Brazil.
Hernandes Faustino
HF
de Carvalho
Department of Pharmacology, University of Campinas (UNICAMP), Campinas, Brazil.
Edson
E
Antunes
Wolfson Centre for Age-Related Diseases, King's College London, London, United Kingdom.
Andrew Douglas
AD
Grant
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002122:Calcium Chloride / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D004558:Electric Stimulation / Q000379:methods; D066298:In Vitro Techniques; D008297:Male; D008610:Menthol / Q000008:administration & dosage* / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology; D050053:TRPM Cation Channels / Q000235:genetics / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology; D001743:Urinary Bladder / Q000502:physiology*
D002121:Calcium Channel Blockers; D050053:TRPM Cation Channels; C492297:TRPM8 protein, mouse; D008610:Menthol; D013779:Tetrodotoxin; D002217:Carbachol; D009543:Nifedipine; D002122:Calcium Chloride