M. Oike et al., AMPLITUDE-MODULATION OF CA2-CELLS( SIGNALS INDUCED BY HISTAMINE IN HUMAN ENDOTHELIAL), Biochimica et biophysica acta. Molecular cell research, 1222(2), 1994, pp. 287-291
We have addressed the problem of whether the agonist concentration sen
sed by endothelial cells is encoded by the sustained rise of the intra
cellular Ca2+ concentration ([Ca2+](i)) or by the frequency of intrace
llular Ca2+ oscillations. Single or confluent endothelial cells from u
mbilical veins were stimulated for 15 min with histamine (0.03 to 100
mu mol/l), and the concomitant changes in [Ca2+](i) were measured with
fura-2/AM. Application of histamine at concentrations above 0.1 mu mo
l/l resulted always in a fast spike of [Ca2+](i), followed by a slow d
ecline to a sustained plateau level, which depends on the presence of
extracellular Ca2+. At the same time of the development of this platea
u phase, quenching of the fura-2/AM signal occurred during agonist sti
mulation in a Ca2+-free, 1.5 mmol/l Mn2+ containing solution, indicati
ng influx of divalent cations during this time. From 48 cells in 1.5 m
mol/l [Ca2+](c) we obtained a close relation between histamine concent
ration and time integral of [Ca2+](i) taken over the 15 min recording
of the plateau [Ca2+](i). The half-maximal increase in the integral of
[Ca2+](i) was at 0.7 mu mol/l for solitary cells, 1.2 mu mol/l for cl
ustered cells and 1.2 mu mol/l for the plateau Ca2+ level. Repetitive
Ca2+ spikes or Ca2+ oscillations appeared only in 16 out of 48 cells,
but their frequency was not correlated to the agonist concentration. C
a2+ oscillations were only observed in a concentration window between
0.1 and 1 mu mol/l histamine, both in single and in clustered endothel
ial cells. Our results indicate that coding of the agonist concentrati
on in endothelial cells is not related to the frequency of Ca2+ oscill
ations, but is closely correlated with the plateau level of intracellu
lar Ca2+.