Am. J. Respir. Cell Mol. Biol., Vol 10, No. 3, 03 1994, 278-283.
Effect of platelet-activating factor on intracellular free calcium in cow tracheal epithelium
M Kondo, J Tamaoki, K Isono, S Takeuchi, Y Ozawa, A Chiyotani and K Konno
First Department of Medicine, Tokyo Women's Medical College, Japan.
The effect of platelet activating factor (PAF) on the intracellular
cytosolic levels of free calcium ([Ca2+]i) was studied in cultured
epithelium from cow trachea. In fura-2-loaded cells, PAF (10(-9) to 10(- 5)
M), but not lyso-PAF, increased [Ca2+]i in a concentration-dependent
manner, from 106 +/- 15 to 270 +/- 40 nM (P < 0.05). This [Ca2+]i
response consisted of a transient increase that peaked within 15 s after
addition and a subsequent sustained elevation that reached a plateau after
1 min. The potency for the sustained response was greater by approximately
1 log U than that for the transient response. Preincubation of the cells
with the PAF receptor antagonist CV6209 (10(- 6) M) inhibited the increase
in [Ca2+]i. Ca(2+)-free medium (2 mM EGTA) totally abolished the sustained
response to PAF, but it only partially inhibited the transient response.
Verapamil (10(-5) M) also largely inhibited the sustained response.
Moreover, PAF transiently increased inositol triphosphate (IP3) levels,
peaking 10 s after addition. These data suggest that (1) a PAF-induced
increase in [Ca2+]i is mediated via PAF receptors, (2) PAF causes both
transient [Ca2+]i release from intracellular stores through IP3 production
and sustained [Ca2+]i influx from extracellular solution, and (3) Ca2+
influx may be a major pathway of PAF-induced increase in [Ca2+]i in cow
tracheal epithelium.
