Receptor-coupled G proteins mediate contraction and Ca++ mobilization in isolated intestinal muscle cells.
Guanosine 5'-O-(gamma-thio)triphosphate (GTP[S]), NaF and cholecystokinin-octapeptide (CCK-8) were used to examine the participation of G proteins in agonist-induced contraction of smooth muscle cells isolated separately from circular and longitudinal muscle layer of guinea pig intestine. All three agents stimulated inositol 1,4,5-triphosphate (InsP3) production and protein kinase C activity to the same extent in permeabilized (GTP[S] and CCK-8) and nonpermeabilized (NaF and CCK-8) muscle cells. InsP3 production was 9 to 13 times higher in circular muscle cells consistent with preferential hydrolysis of phosphatidylinositol 4,5-biphosphate in this cell type. InsP3 production and protein kinase C activation in permeabilized muscle cells were abolished by guanosine 5'-O-(beta-thio)diphosphate (10 microM). Maximal concentrations of GTP[S] (100 microM), CCK-8 (1 nM) and InsP3 (1 microM) elicited similar increases in [Ca++]i, net 45Ca++ efflux and contraction in permeabilized circular, but not longitudinal, muscle cells [( Ca++]i: 224 +/- 35 nM, 279 +/- 29 nM and 288 +/- 45 nM increase above basal level; 45Ca++ efflux: 35 +/- 2%, 34 +/- 3% and 37 +/- 3% decrease in cell Ca++ content; contraction: 26 +/- 2%, 24 +/- 2% and 25 +/- 2% decrease in cell length). The responses to GTP[S] and CCK-8 were abolished by guanosine 5'-O-(beta-thio)diphosphate (10 microM) and heparin (10 micrograms/ml), whereas the response to InsP3 was abolished by heparin only. Maximal concentrations of NaF and CCK-8 elicited similar increases in [Ca++]i and contraction in nonpermeabilized circular and longitudinal muscle cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Murthy
K S
KS
Department of Medicine, Medical College of Virginia, Richmond.
Grider
J R
JR
Makhlouf
G M
GM
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006168:Guinea Pigs; D006493:Heparin / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007422:Intestines / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D010716:Phosphatidylinositols / Q000378:metabolism; D011493:Protein Kinase C / Q000187:drug effects / Q000378:metabolism; D012844:Sincalide / Q000494:pharmacology; D012969:Sodium Fluoride / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology
D010716:Phosphatidylinositols; D013873:Thionucleotides; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C023427:guanosine 5'-O-(2-thiodiphosphate); D015544:Inositol 1,4,5-Trisphosphate; D012969:Sodium Fluoride; D006493:Heparin; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D012844:Sincalide; D002118:Calcium