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 ago
nist-mediated effects must reside in their ability to regulate the oscillat
ing 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+ rel
ease in resting HeLa cells and a transient increase in the frequency of ong
oing Ca2+ oscillations stimulated by histamine. Two poorly metabolizable an
alogs 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 oscillatio
ns. Complete inhibition of Ins (1,4,5)P-3 3-kinase (IP3K) by either adriamy
cin or its specific antibody blocked Ca2+ oscillations. Partial inhibition
of IP3K causes a significant reduction in frequency. Taken together, our re
sults 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.