Effects of GTP gamma S on muscarinic receptor-stimulated inositol phospholipid hydrolysis in permeabilized smooth muscle from the small intestine.
1. Smooth muscle fragments from the longitudinal layer of the small intestine of the guinea-pig were permeabilized with Staphylococcus aureus alpha toxin (alpha-toxin) and used to investigate the role of G-protein activation in the regulation of muscarinic acetylcholine receptor (AChR)-stimulated inositol phospholipid hydrolysis. 2. The efficiency of alpha-toxin permeabilization was estimated by the release of [3H]-2-deoxyglucose ([3H]-2DG) after prior loading or lactate dehydrogenase (LDH) enzyme release from the smooth muscle fragments. 3. In alpha-toxin-permeabilized smooth muscle, but not in non-permeabilized muscle, GTP gamma S induced time- and concentration-dependent increases in labelled inositol phosphates. Carbachol (CCh) increased labelled inositol phosphates in both permeabilized and non-permeabilized muscle, although the increases were greater in non-permeabilized smooth muscle. The response to 100 microM CCh was severely reduced by 0.5 microM atropine. 4. In permeabilized muscle the effects of GTP gamma S or CCh on inositol phosphate levels were reduced by treatment with pertussis toxin (PTX) and completely inhibited by GDP beta S. 5. GTP gamma S caused a concentration-dependent inhibition of the CCh-induced increases in the levels of labelled inositol phosphates. Dibutyryl cyclic AMP or Sp-cAMPs (adenosine-3',5'-cyclic phosphorothiolate-Sp) reduced the effects of CCh on inositol phosphate levels. 6. The results suggest that muscarinic AChR activation induces inositol phospholipid hydrolysis via more than one G-protein in this smooth muscle and that several mechanisms may contribute to the modulation of both stimulatory and inhibitory responses observed.
Prestwich
S A
SA
Department of Pharmacology and Clinical Pharmacology, St George's Hospital Medical School, London.
Miyazaki
H
H
Bolton
T B
TB
D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D002463:Cell Membrane Permeability; D002851:Chromatography, High Pressure Liquid; D000242:Cyclic AMP / Q000378:metabolism; D003847:Deoxyglucose / Q000378:metabolism; D004347:Drug Interactions; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology*; D006168:Guinea Pigs; D006868:Hydrolysis; D007295:Inositol Phosphates / Q000378:metabolism*; D007421:Intestine, Small / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D009130:Muscle, Smooth / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000145:classification / Q000187:drug effects / Q000378:metabolism*; D010738:Type C Phospholipases / Q000494:pharmacology
D007295:Inositol Phosphates; D010743:Phospholipids; D011976:Receptors, Muscarinic; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D002217:Carbachol; D003847:Deoxyglucose; D000242:Cyclic AMP; D007770:L-Lactate Dehydrogenase; D010738:Type C Phospholipases