Valentino - just save the structure to handles in one callback so that the other callback has access to it. For example, if the following is the callback to choose and load the contents of a file
function pushbutton1_Callback(hObject, eventdata, handles)
handles.myData = myData;
Now in your other callback, you can access this structure directly as
function pushbutton2_Callback(hObject, eventdata, handles)
Try implementing the above and see what happens!