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Three distinct muscarinic signalling pathways for cationic channel activation in mouse gut smooth muscle cells
Author(s) -
Sakamoto Takashi,
Unno Toshihiro,
Kitazawa Takio,
Taneike Tetsuro,
Yamada Masahisa,
Wess Jürgen,
Nishimura Masakazu,
Komori Seiichi
Publication year - 2007
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2007.133165
Subject(s) - muscarinic acetylcholine receptor , carbachol , chemistry , endocrinology , medicine , wild type , microbiology and biotechnology , biophysics , mutant , receptor , biology , biochemistry , gene
Using mutant mice genetically lacking certain subtypes of muscarinic receptor, we have studied muscarinic signal pathways mediating cationic channel activation in intestinal smooth muscle cells. In cells from M 2 subtype‐knockout (M 2 ‐KO) or M 3 ‐KO mice, carbachol (100 μ m ) evoked a muscarinic cationic current (m I Cat ) as small as ∼10% of m I Cat in wild‐type (WT) cells. No appreciable current was evoked in M 2 /M 3 double‐KO cells. All mutant type cells preserved normal G‐protein–cationic channel coupling. The M 3 ‐KO and WT m I Cat each showed a U‐shaped current–voltage ( I–V ) relationship, whereas the M 2 ‐KO m I Cat displayed a linear I–V relationship. Channel analysis in outside‐out patches recognized 70‐pS and 120‐pS channels as the major muscarinic cationic channels. Active patches of M 2 ‐KO cells exhibited both 70‐pS and 120‐pS channel activity usually together, either of which consisted of brief openings (the respective mean open times O τ = 0.55 and 0.23 ms). In contrast, active M 3 ‐KO patches showed only 70‐pS channel activity, which had three open states (O τ = 0.55, 3.1 and 17.4 ms). In WT patches, besides the M 2 ‐KO and M 3 ‐KO types, another type of channel activity was also observed that consisted of 70‐pS channel openings with four open states (O τ = 0.62, 2.7, 16.9 and 121.1 ms), and patch current of this channel activity showed a U‐shaped I–V curve similar to the WT m I Cat . The present results demonstrate that intestinal myocytes are endowed with three distinct muscarinic pathways mediating cationic channel activation and that the M 2 /M 3 pathway targeting 70‐pS channels, serves as the major contributor to m I Cat generation. The delineation of this pathway is consistent with the formation of a functional unit by the M 2 ‐G o protein and the M 3 ‐PLC systems predicted to control cationic channels.