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Signal transduction pathways of muscarinic receptor mediated activation in the newborn and adult mouse urinary bladder
Author(s) -
Ekman Mari,
Andersson KarlErik,
Arner Anders
Publication year - 2009
Publication title -
bju international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.773
H-Index - 148
eISSN - 1464-410X
pISSN - 1464-4096
DOI - 10.1111/j.1464-410x.2008.07935.x
Subject(s) - methoctramine , muscarinic acetylcholine receptor , carbachol , muscarinic acetylcholine receptor m3 , thapsigargin , endocrinology , medicine , muscarinic acetylcholine receptor m2 , chemistry , iberiotoxin , muscarinic acetylcholine receptor m1 , ryanodine receptor , receptor , biology , calcium , potassium channel
OBJECTIVE To study the role of M 2 and M 3 muscarinic receptor subtypes, sources of activator Ca 2+ , and mechanisms involved in increased force oscillations in muscarinic contractions in the bladders of newborn and adult mice, as in the adult bladder muscarinic M 3 receptors are considered to mediate the main part of bladder contraction, and this has not been established in the newborn bladder. MATERIALS AND METHODS Bladder preparations from newborn (0–2 days) and adult (10–12 weeks) mice were mounted for in vitro force registration and activated with carbachol and high‐K + solution in the presence of M 3 (4‐DAMP 30 n m ) or M 2 (methoctramine, 100 n m ) receptor antagonists. Thapsigargin (1 µ m ) or ryanodine (10 µ m ) were used to inhibit sarcoplasmic reticulum Ca 2+ release. L‐NAME (300 µ m ) and 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one (ODQ; 10 µ m ) were used to inhibit nitric oxide synthase and guanylyl cyclase, respectively. Gap‐junction function was inhibited with by 18‐β‐glycyrrhetinic acid (18‐β‐GA; 0.1–100 µ m ). Big‐conductance (BK) and small‐conductance (SK) K + channels were inhibited by apamine and charybdotoxin (0.3 µ m ), respectively. RESULTS Concentration–response relations for carbachol in the presence of 4‐DAMP and methoctramine showed that M 3 receptors are the main activating pathway also in the newborn bladder. Neither thapsigargin nor ryanodine influenced the muscarinic responses of the newborn and adult bladders. Carbachol‐induced contractions were not influenced by L‐NAME or ODQ. The 18‐β‐GA inhibited carbachol‐induced contractions in both newborn and adult tissue in a similar manner. Apamine and charybdotoxin slightly increased the amplitude of the contractile responses. CONCLUSION These results suggest that in the newborn mouse bladder, as in adult bladders, the M 3 muscarinic receptor subtype is mainly responsible for carbachol‐induced contractile responses. The main mechanism for muscarinic receptor‐induced activation is influx of Ca 2+ from the extracellular medium, and there seems to be no major contribution of Ca 2+ release from intracellular stores. The phasic contractile activity induced by carbachol in the newborn bladder is not influenced by gap junction inhibition and does not involve SK and BK channels.