Okadaic acid, a potent PP2A-type inhibitor, does not alter NHE3 gel mobility or NHE3 phosphorylation at serine 552 or 605. A: OKP cells were treated with vehicle, CA for 30 min, or okadaic acid at 10−6 M (OkA) for 30 or 60 min and then solubilized, subjected to SDS-PAGE, and immunoblotted with anti-NHE3, anti-PS552, monoclonal anti-PS605, or anti-GAPDH antibody. B: densitometric analysis of multiple similar experiments in which OKP cells were treated with vehicle, OkA, or F/I for 30 min and then solubilized, subjected to SDS-PAGE, and immunoblotted with anti-NHE3, anti-PS552, or anti-PS605 antibody. Anti-PS552 and anti-PS605 signals were normalized to total NHE3 signals for the same experiment. Data are means + SE; n = 5–6 for Ctrl, n = 5–6 for OkA, and n = 4–6 for F/I. P values were calculated using a paired t-test. *P < 0.05 compared with control.