Oxidative stress reduces the muscarinic receptor function in the urinary bladder.
OBJECTIVE
Several pathophysiological conditions in the urinary bladder, for example, ischemia/reperfusion and inflammation are characterized by the formation of reactive oxygen species (ROS). The ROS are highly toxic because they can destroy proteins, DNA, and lipids. The aim of this study was to investigate the effect of oxidative stress on excitation-contraction coupling of detrusor smooth muscle.


METHODS
Smooth muscle strips were dissected from pig urinary bladder and mounted in organ baths. Oxidative stress was mimicked by the addition of Cumene hydroperoxide (CHP), a lipophilic hydroperoxide, to the organ baths. Contractile responses to electrical field stimulation (EFS: 4-32 Hz), carbachol (10(-8)-3 x 10(-5) M), potassium (65.3 mM), and ATP (1 mM) were monitored before and after the addition of CHP.


RESULTS
Responses of detrusor strips to EFS were for the greater part based on neurogenic stimulation and the release of acetylcholine. CHP diminished contractile responses to EFS and carbachol to the same extent. The pD(2) value of the carbachol concentration-response curve decreased significantly after exposure to 0.1 mM, 0.4 mM, 0.8 mM CHP. Furthermore the maximal effect obtained with carbachol was significantly reduced after 0.1 mM, 0.4 mM, and 0.8 mM CHP treatment. Contractions induced by potassium and ATP were significantly less affected by oxidative stress compared to EFS- and carbachol-induced responses of comparable amplitude.


CONCLUSIONS
The results of our study demonstrate that oxidative stress induced by CHP affects pig bladder contractility. The muscarinic receptor signaling system is severely damaged. L-type calcium channels and the contractile system are less affected and cholinergic nerves remain largely unaffected.
de Jongh
Rik
R
Department of Urology, University Hospital Maastricht, P. Debyelaan 25, 6202 AZ Maastricht, The Netherlands. RDJ@urology.azm.nl
Haenen
Guido R M M
GR
van Koeveringe
Gommert A
GA
Dambros
Miriam
M
De Mey
Jo G R
JG
van Kerrebroeck
Philip E V
PE
D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D001555:Benzene Derivatives / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005609:Free Radicals; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects; D015227:Lipid Peroxidation / Q000187:drug effects; D009119:Muscle Contraction / Q000502:physiology; D016877:Oxidants / Q000494:pharmacology; D018384:Oxidative Stress / Q000502:physiology*; D010275:Parasympathetic Nervous System / Q000502:physiology; D011189:Potassium Chloride / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000502:physiology*; D013552:Swine; D013779:Tetrodotoxin / Q000494:pharmacology; D001743:Urinary Bladder / Q000502:physiology*
D000779:Anesthetics, Local; D001555:Benzene Derivatives; D020746:Calcium Channels, L-Type; D005609:Free Radicals; D016877:Oxidants; D011976:Receptors, Muscarinic; D013779:Tetrodotoxin; D011189:Potassium Chloride; C007164:cumene hydroperoxide