Signaling pathways in the biphasic effect of ANG II on Na+/H+ exchanger in T84 cells

The effect of ANG II on pH(i), [Ca2+](i) and cell volume was investigated in T84 cells, a cell line originated from colon epithelium, using the probes BCECF-AM, Fluo 4-AM and acridine orange, respectively. The recovery rate of pHi via the Na+/H+ exchanger was examined in the first 2 min following the acidification of pHi with a NH4Cl pulse. In the control situation, the pHi recovery rate was 0.118 +/- 0.001 (n = 52) pH units/inin and ANG II (10(-12) M or 10(-9) m) increased this value (by 106% or 32%, respectively) but ANG II (10(-7) m) decreased it to 47%. The control [Ca2+](i) was 99 +/- 4 (n = 45) nM and ANG II increased this value in a dose-dependent manner. The ANG II effects on cell volume were minor and late and should not interfere in the measurements of pHi recovery and [Ca2+](i). To document the signaling pathways in the hormonal effects we used: Staurosporine (a PKC inhibitor), W13 (a calcium-dependent calmodulin antagonist), H89 (a PKA inhibitor) or Econazole (an inhibitor of cytochrome P450 epoxygenase). Our results indicate that the biphasic effect of ANG II on Na+/H+ exchanger is a cAMP-independent mechanism and is the result of. 1) stimulation of the exchanger by PKC signaling pathway activation (at 10(-12) - 10(-7) m ANG IT) and by increases of [C(a)2(+)](i) in the lower range (at 10(-12) M ANG II) and 2) inhibition of the exchanger at high [Ca2+](i) levels (at 10(-9) - 10(-7) m ANG II) through cytochrome P450 epoxygenase-dependent metabolites of the arachidonic acid signaling pathway.