I have 2 columns in a list, Text for people to see and the key. How do I extract the KEY's value to pass to a new page? Below is what I'm trying'

private void MmButton1_Click(object sender, System.EventArgs e)
{
string ptPage = MmDropDownList2.BindingSourceValueMember.ToString() ;
string strURL = String.Concat("ptos.aspx?ptoapp=", ptPage );
Response.Redirect(strURL);
}

In my address line I see :
http://localhost/mmJumpStart/ptos.aspx?ptoapp=pi_applpg

The pi_applpg is the column, not it's coresponding value.

TIA

__Stephen