ISSN:
1573-4919
Keywords:
muscarinic receptors
;
GTP-binding proteins
;
phosphoinositides
;
adenylate cyclase
;
smooth muscle
;
caecum
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
Abstract The effects of muscarinic acetylcholine receptor stimulation on phosphoinositides breakdown and adenylate cyclase activity were examined in the circular smooth muscle of the rabbit caecum. InMyo-[3H]inositol-labeled circular smooth muscle cells, carbachol caused a concentration-dependent increase in [3H]inositol phosphates ([3H]IPs) accumulation (EC50 of 3±1 μM). The M1-selective antagonist pirenzepine (PRZ), the M2-selective AF-DX 116 (11-2[[2-[(diethyl-amino)methyl]-1-piperidinyl]acetyl]-5, 11-dihydro-6Hpyrido[2,3-b][1,4]benzodiazepin-6-one) and the M3-selective para-fluoro-hexahydrosiladifenidol (p-F-HHSiD) inhibited the carbachol-induced [3]inositol phosphates accumulation with the following order of potency: p-F-HHSiD〉PRZ〉AF-DX 116. In saponin-permeabilized circular smooth muscle cells, carbachol and GTPγ[S] elicited a concentration-dependent increase in [3H]inositol phosphates accumulation. The concentration-response curve for GTPγ[S] was shifted to the left when cells were incubated with 1 μM carbachol. The [3H]inositol phosphates accumulation elicited by simultaneous addition of 0.1 μM GTPγ[S] and 1 μM carbachol to permeabilized cells was significantly decreased (78.28±18.23% inhibition) when cells were preincubated for 5 min with 0.1 mM GDPβ[S]. In nonpermeabilized cells, pertussis toxin did not alter the carbachol-induced increase in [3H]inositol phosphates accumulation. On the other hand, the 0.1 mM carbachol-induced inhibition of forskolin-stimulated adenylate cyclase activity in circular smooth muscle homogenates was significantly reversed by atropine and AF-DX 116, whereas PRZ and p-F-HHSiD were ineffective (muscarinic antagonists were used at 1 μM final concentration). Moreover, the carbachol-induced inhibition of the cyclic AMP accumulation elicited by 10 μM isoproterenol was abolished by pertussis toxin pretreatment of isolated circular smooth muscle cells. In conclusion, our data suggest that in circular smooth muscle of rabbit caecum, the muscarinic receptor stimulation of [3H]inositol phsophates accumulation is mediated by M3 subtype receptors coupled to a pertussis toxin-insensitive G protein, whereas inhibition of adenylate cyclase activity is mediated by M2 subtype receptors coupled to a pertussis toxin-sensitive GTP-binding protein Gi.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00928367
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