Effects of polyamines and calcium and sodium ions on smooth muscle cytoskeleton-associated phosphatidylinositol (4)-phosphate 5-kinase
✍ Scribed by H. Chen; C. B. Baron; T. Griffiths II; P. Greeley; R. F. Coburn
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 310 KB
- Volume
- 177
- Category
- Article
- ISSN
- 0021-9541
No coin nor oath required. For personal study only.
✦ Synopsis
phosphatidylinositol (4)-phosphate 5-kinase plays a critical role in the regulation of membrane concentrations of phosphatidylinositol (4,5)-bisphosphate and formation of inositol (1,4,5)-trisphosphate. In unstimulated porcine trachealis smooth muscle, 70% of total cellular phosphatidylinositol (4)-phosphate 5-kinase activity was associated with cytoskeletal proteins and only trace activity was detectable in isolated sarcolemma. Using two different preparations, we studied cytoskeleton-associated phosphatidylinositol (4)-phosphate 5-kinase under conditions that attempted to mimic the ionic and thermal cytoplasmic environment of living cells. The cytoskeletonassociated enzyme, studied using phosphatidylinositol (4)-phosphate substrate concentrations that produced phosphatidylinositol 4,5-bisphosphate at about 10% of the maximal rate, was sensitive to free [Mg 2/ ], had an absolute requirement for phosphatidylserine, phosphatidic acid, or phosphatidylinositol, and included type I isoforms. At 0.5 mM free [Mg 2/ ], physiological spermine concentrations, 0.2-0.4 mM, increased phosphatidylinositol (4)-phosphate 5-kinase activity two to four times compared to controls run without spermine. The EC 50 for spermine-evoked increases in activity was 0.17 { 0.02 mM. Spermine-evoked enzyme activity was a function of both free [Mg 2/ ] and substrate concentration. Cytoskeleton-associated phosphatidylinositol (4)-phosphate 5-kinase was inhibited by free [Ca 2/ ] over a physiological range for cytoplasm 0 10 08 to 10 05 M, an effect independent of the presence of calmodulin. Na / over the range 20 to 50 mM also inhibited this enzyme activated by 5 mM Mg 2/ but had no effect on spermine-activated enzyme. Na / , Ca 2/ , and spermine appear to be physiological modulators of smooth muscle cytoskeletonbound phosphatidylinositol (4)-phosphate 5-kinase.