Carbamoylcholine regulation of polyphosphoinositide synthesis and hydrolysis in cultured, dispersed, digitonin-permeabilized mouse pancreatic islet cells.
Continuing formation of inositol phosphates during stimulation of pancreatic beta-cells by hormones and neurotransmitters requires the continued synthesis of the polyphosphoinositides phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5 bisphosphate (PIP2) from phosphatidylinositol (PI). In the present study we have investigated how this pathway and the activity of phosphoinositide-specific phospholipase C (PI-PLC) are regulated by carbamoylcholine (CCh), Ca2+, the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA), GTP gamma S and NaF in 44-h [3H]inositol-labelled, dispersed and digitonin-permeabilized mouse pancreatic islet cells. CCh stimulated not only PI-PLC (G-protein-mediated) but also, by an as yet unknown mechanism, significantly enhanced PI 4-kinase activity, estimated as the PIP:PI ratio, by 100%, and further increased the flux from PI to PIP and PIP2, GTP gamma S and NaF mimicked the effects of CCh on PI-PLC but had no effect on the levels of PIP and PIP2, TPA raised the PIP:PI ratio by 75%. In addition TPA counteracted the CCh stimulation of PI-PLC. There was no effect of 10(-6) mol/l Ca2+ on the levels of PIP and PIP2. Experiments with quinacrine and adenosine confirmed that PI-PLC and PI 4-kinase could be regulated independently of each other. In conclusion, these data point to differential regulation of polyphosphoinositide synthesis and breakdown.
Kardasz
A M
AM
Department of Medical Biochemistry and Genetics, Panum Institute, University of Copenhagen, Denmark.
Thams
P
P
Capito
K
K
Hedeskov
C J
CJ
D019870:1-Phosphatidylinositol 4-Kinase; D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D002478:Cells, Cultured; D004072:Digitonin / Q000494:pharmacology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D007515:Islets of Langerhans / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D010539:Permeability; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D012969:Sodium Fluoride / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism
D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; C060980:phosphatidylinositol 3,4-diphosphate; C037178:phosphatidylinositol 4-phosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D002217:Carbachol; D012969:Sodium Fluoride; D017853:Phosphotransferases (Alcohol Group Acceptor); D019870:1-Phosphatidylinositol 4-Kinase; D010738:Type C Phospholipases; D004072:Digitonin; D013755:Tetradecanoylphorbol Acetate