Inositol tetrakisphosphate as a frequency regulator in calcium oscillations in HeLa cells

Cellular signaling mediated by inositol (1,4,5)trisphosphate (Ins(1,4,5)P-3) results in oscillatory intracellular calcium (Ca2+) release. Because the amplitude of the Ca2+ spikes is relatively invariant, the extent of the agonist-mediated effects must reside in their ability to regulate the oscillating frequency. Using electroporation techniques, we show that Ins(1,4,5)P-3, Ins(1,3,4,5)P-4, and Ins(1,3,4,6)P-4 cause a rapid intracellular Ca2+ release in resting HeLa cells and a transient increase in the frequency of ongoing Ca2+ oscillations stimulated by histamine. Two poorly metabolizable analogs of Ins(1,4,5)P-3, Ins(2,4,5)P-3, and 2,3-dideoxy-Ins(1,4,5)P-3, gave a single Ca2+ spike and failed to alter the frequency of ongoing oscillations. Complete inhibition of Ins (1,4,5)P-3 3-kinase (IP3K) by either adriamycin or its specific antibody blocked Ca2+ oscillations. Partial inhibition of IP3K causes a significant reduction in frequency. Taken together, our results indicate that Ins(1,3,4,5)P-4 is the frequency regulator in vivo, and IP3K, which phosphorylates Ins(1,4,5)P-3 to Ins(1,3,4,5)P-4, plays a major regulatory role in intracellular Ca2+ oscillations.