Ja. Felix et al., PKC activation inhibits Ca2+ signaling in tracheal epithelial cells kept in simulated microgravity, J APP PHYSL, 89(2), 2000, pp. 855-864
Microgravity has been shown to alter protein kinase C (PKC) activity; there
fore, we investigated whether microgravity influences mechanically stimulat
ed Ca2+ signaling and ATP-induced Ca2+ oscillations, both of which are modu
lated by PKC. Rabbit tracheal epithelial outgrowth cultures or suspended ep
ithelial sheets were rotated in bioreactors to simulate microgravity. Mecha
nical stimulation of a single cell increased the cytosolic Ca2+ concentrati
on in 35-55 cells of both outgrowth cultures and epithelial sheets kept at
unit gravity (G) or in simulated microgravity (s mu G). In outgrowth cultur
es, 12-O-tetradecanoylphorbol-13-acetate (TPA; 80 nM), a PKC activator, res
tricted Ca2+ "waves" to about 10 cells in unit G and to significantly fewer
cells in s mu G. TPA only slightly reduced the spread of Ca2+ waves in epi
thelial sheets kept in s mu G but did not inhibit Ca2+ waves of sheets kept
in unit G. In both cell preparations from both conditions, TPA inhibited A
TP-induced Ca2+ oscillations; however, the effect was more pronounced in ce
lls kept in s mu G. These results suggest that PKC activation is more robus
t in cells subjected to s mu G.