Acetylcholine increases the breakdown of triphosphoinositide of rabbit iris muscle prelabelled with [32P] phosphate

One of the pair was incubated at 37 degrees C for 10 min in unlabelled medium containing 10mM-2-deoxyglucose and the other was incubated in the presence of acetylcholine plus eserine. 2-Deoxyglucose, which was included in the incubation medium to minimize the biosynthesis of triphosphoinositide from ATP and diphosphoinositide, decreased the amount of labelled ATP by 71% and inhibited further 32P incorporation from ATP into triphosphoinositide by almost 30%. 3

A A Abdel-Latif; R A Akhtar; J N Hawthorne

2015

Key concepts

Scholarcy highlights

  • 1. Paired iris smooth muscles from rabbits were incubated for 30 min at 37 degrees C in an iso-osmotic salt medium containg glucose, inositol, cytidine andphosphate
  • One of the pair was incubated at 37 degrees C for 10 min in unlabelled medium containing 10mM-2-deoxyglucose and the other was incubated in the presence of acetylcholine plus eserine. 2-Deoxyglucose, which was included in the incubation medium to minimize the biosynthesis of triphosphoinositide from ATP and diphosphoinositide, decreased the amount of labelled ATP by 71% and inhibited further 32P incorporation from ATP into triphosphoinositide by almost 30%. 3
  • The triphosphoinositide effect was blocked by atropine but not by D-tubocurarine
  • Acetylcholine decreased by 28% the 32P incorporation into triphosphoinositide, presumably by stimulating its breakdown
  • This decrement in triphosphoinositide was blocked by atropine, but not by D-tubocurarine. 6
  • The presence of triphosphoinositide phosphomonoesterase, the enzyme that might be stimulated in the iris smooth muscle by the neurotransmitter, was demonstrated, and, under our methods of homogenization and assay, more than 80% of its activity was localized in the particulate fraction

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