  We study the selfenergy of the $\Theta^+$ pentaquark in nuclei associated
with two types of interaction: the KN decay of the $\Theta^+$ and two meson
baryon decay channels of the $\Theta^+$. Whereas the potential related to the
first source is quite weak, the second kind of interaction produces a large and
attractive potential that could lead to the existence of $\Theta^+$ nuclear
bound states.
