Muscarinic Receptor Induced Contractions of the Detrusor are Mediated by Activation of TRPC4 Channels.
Muscarinic receptor mediated contractions of the detrusor rely on Ca2+influx through voltage-gated Ca2+channels but to our knowledge the mechanism linking stimulation of M3Rs to the activation of voltage dependent Ca2+channels has not been established. TRPC4 channels are receptor operated cation channels that couple muscarinic receptor activation to depolarization of intestinal smooth muscle cells, voltage-activated Ca2+influx and contraction. We investigated whether TRPC4 channels are involved in cholinergic mediated contractions of the detrusor.



Isometric tension recordings were made on strips of murine detrusor and intracellular Ca2+measurements were made on isolated detrusor myocytes using confocal microscopy. Transcriptional expression of TRPC and IP3R subtypes in intact detrusor strips and isolated detrusor myocytes was assessed using reverse transcriptase-polymerase chain reaction.



Cholinergic stimulation of the detrusor induced by electrical field stimulation or exogenous application of carbachol or neostigmine evoked contractions consisting of a transient plus a tonic response, which was blocked by ML204, an inhibitor of TRPC4 channels. A phasic oscillatory component was blocked by the IP3R inhibitor 2-APB. Carbachol evoked reproducible Ca2+responses in isolated detrusor myocytes, consisting of an initial Ca2+transient followed by Ca2+oscillations. ML204 inhibited the initial Ca2+transient whereas 2-APB inhibited the Ca2+oscillations. Reverse transcriptase-polymerase chain reaction experiments showed that TRPC4β, TRPC6 and IP3R1 were selectively expressed in isolated detrusor myocytes. Control experiments demonstrated that ML204 did not affect L-type Ca2+or BK current amplitude, caffeine induced Ca2+transients or KCl induced contractions of the detrusor.



Muscarinic receptor mediated contractions of the detrusor involve the activation of TRPC4β channels.
Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Ireland.
Caoimhin S
CS
Griffin
Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Ireland.
Eamonn
E
Bradley
Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Ireland.
Srikanth
S
Dudem
Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Ireland.
Mark A
MA
Hollywood
Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Ireland.
Noel G
NG
McHale
Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Ireland.
Keith D
KD
Thornbury
Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Ireland. Electronic address: gerard.sergeant@dkit.ie.
Gerard P
GP
Sergeant
D000818:Animals; D005260:Female; D008297:Male; D008810:Mice, Inbred C57BL; D009119:Muscle Contraction / Q000502:physiology*; D009130:Muscle, Smooth / Q000502:physiology*; D011976:Receptors, Muscarinic / Q000502:physiology*; D050052:TRPC Cation Channels / Q000502:physiology*; D001743:Urinary Bladder / Q000502:physiology*
D011976:Receptors, Muscarinic; D050052:TRPC Cation Channels; C489571:TRPC4 ion channel
acetylcholine; cholinergic agents; muscle contraction; transient receptor potential channels; urinary bladder