Muscarinic receptor-activated cationic channels in murine ileal myocytes.
OBJECTIVE
There is little information about the excitatory cholinergic mechanisms of mouse small intestine although this model is important for gene knock-out studies.


METHODS
Using patch-clamp techniques, voltage-dependent and pharmacological properties of carbachol- or intracellular GTPgammaS-activated cationic channels in mouse ileal myocytes were investigated.


RESULTS
Three types of cation channels were identified in outside-out patches (17, 70 and 140 pS). The voltage-dependent behaviour of the 70 pS channel, which was also the most abundantly expressed channel (approximately 0.35 micro(-2)) was most consistent with the properties of the whole-cell muscarinic current (half-maximal activation at -72.3+/-9.3 mV, slope of -9.1+/-7.4 mV and mean open probability of 0.16+/-0.01 at -40 mV; at near maximal activation by 50 microM carbachol). Both channel conductance and open probability depended on the permeant cation in the order: Cs+ (70 pS) >Rb+ (66pS) >Na+ (47 pS) >Li+ (30 pS). External application of divalent cations, quinine, SK&F 96365 or La3+ strongly inhibited the whole-cell current. At the single channel level the nature of the inhibitory effects appeared to be very different. Either reduction of the open probability (quinine and to some extent SK&F 96365 and La3+) or of unitary current amplitude (Ca2+, Mg2+, SK&F 96365, La3+) was observed implying significant differences in the dissociation rates of the blockers.


CONCLUSIONS
The muscarinic cation current of murine small intestine is very similar to that in guinea-pig myocytes and murine genetic manipulation should yield important information about muscarinic receptor transduction mechanisms.
Dresviannikov
A V
AV
Department of Nerve-Muscle Physiology, Laboratory of Molecular Pharmacology of Cellular Receptors and Ion Channels, Bogomoletz Institute of Physiology, Kiev, Ukraine.
Bolton
T B
TB
Zholos
A V
AV
D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology; D005260:Female; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000502:physiology; D007082:Ileum / Q000166:cytology / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000502:physiology*; D050051:Transient Receptor Potential Channels / Q000235:genetics / Q000378:metabolism*
D018679:Cholinergic Agonists; D011976:Receptors, Muscarinic; D050051:Transient Receptor Potential Channels; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D002217:Carbachol