[Gtk-sharp-list] how can I get value in CellRendererCombo with multicolumn Model?

[Dr. McArrow]

I have a CellRendererCombo in a treeview.
how can I retrive a value from a column different than the one defined by  
TextColumn?
My ListStore holds two values: an id from a database and a string.
TextColumn points to the string (column 0), but I want to know the id (col  
1).


ListStore ls_dept = new ListStore(typeof(string),typeof(string));
ls_dept.AppendValue("sssss","1");
ls_dept.AppendValue("zzzzz","2")

...

CellRendererCombo crc = new CellRendererCombo();
crc.Editable = true;
crc.Model = ls_dept;
crc.TextColumn = 0;
crc.Edited += (OnEdited);
...

private void OnEdited(object o, EventArgs a)
{
in this place i need to know the value of column 1.
how can I do this?
}


-- 
Dr.McArrow