Calling an event when value changes on a databound dropdown

I have a databound dropdown box that displays a list of customers, when I choose the customer, I want to call an event caled AccountLookUp that populates controls from a spoc that was called. When I select a customer, the OnTextChanged event does not fire, any ideas?
 
<asp:DropDownList ID="ddAccount" runat="server" Width="360px" style="top: 216px; left: 95px;
            position: absolute; height: 22px;"
            DataSourceID="SqlDataSource1" DataTextField="cmf"
            DataValueField="cmf" TabIndex="1" maxlength="100" OnTextChanged="AccountLookUp"></asp:DropDownList> 
 
Thank you
Edski

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