Action Pane accessing to control populated inside

[Diego G]

I create an action pane base on user control, on the user control I add a
text box and a combo box. Now how I can upload the items on the Combo box
from outside of the Action Pane.
I try the following:
1) Put the combo box as public.
2) Access the action pane.
Everything that I try, not allow me to access to the combo box control.

How I can access to the controls that are under the Action Pane / user
Control.