  Giant oxygen isotope effects observed in colossal magnetoresistance
manganites are investigated by employing the combined model of the double
exchange and interacting lattice polaron mechanism. We have shown that the
isotope effects on $ T_C$ in the metallic phase and $ T_{CO}$ in the charge
ordered phase of manganites can be explained well in terms of the double
exchange and polaron narrowing factors with reasonable physical parameters.
