Inositol trisphosphate kinase activity in hypertrophied rat heart

In the present experiment, we demonstrated that IP3 kinase activity was increased in SHRSP heart compared to WKY heart. IP3 kinase activity in the heart was highest in the cytosolic fraction in both SHRSP and WKY. Its activity progressively increased with age in 5- to 20-week SHRSP. The activity reached about three times the level of 5-week-old SHRSP in 40-week-old SHRSP. On the other hand, in WKY it was 1.3-fold at 40 weeks compared with that at 5 weeks. We determined the effect of divalent cations on IP3 kinase activity. Ca2+ stimulated its activity in a dose-dependent manner at 10(-9) to 10(-6) M. In SHRSP it was enhanced about 2.1-fold at 10(-6) M of Ca2+, but in WKY it was 1.5-fold at 1.0(-6) M of Ca2+. Mn2+ also stimulated IP3 kinase activity in both groups of animals, while, Fe2+, Zn2+, and Cu2+ inhibited IP3 kinase activity. In our experiment IP3 kinase activity was increased in SHRSP and its activity was markedly affected by divalent cations. These data suggest that the accumulations of IP3 and IP4 after hormonal stimulation play a physiologic role, possibly by alteration of Ca2+ levels in cardiac tissue.