Eur J Endocrinol
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DOI: 10.1530/eje.0.1360539
European Journal of Endocrinology, Vol 136, Issue 5, 539-545
Copyright © 1997 by European Society of Endocrinology
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Carbamoylcholine regulation of polyphosphoinositide synthesis and hydrolysis in cultured, dispersed, digitonin-permeabilized mouse pancreatic islet cells

Andrew M Kardasz, Peter Thams, Kirsten Capito and Carl J Hedeskov

Continuing formation of inositol phosphates during stimulation of pancreatic β-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.

European Journal of Endocrinology 136 539–545






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