dropdownlist autopostback when editing in datagrid

[Arthur]

I have multiple dropdownlists in edit mode of my datagrid.
list 1 effects the members of list 2
i.e.
list 1 --> department
list 2 --> department members

when a user select a new department in the dropdownlist I
want to re-populate the members list dependent on the
department selected

Normally I use the autopostback feature but I cannot get
that to work inside the datagrid

bindDepartment and BindMembers are functions used to
initiall populate the lists

below is the first dropdownlist
<edititemtemplate>
<asp:dropdownlist Width="90px" ID="Department"
CssClass="Standard-text" DataSource='<%# BindDepartment
(_timeEdit.Department) %>' DataTextField="Department"
DataValueField="Department" Runat="server" >
</asp:dropdownlist>
</edititemtemplate>

<edititemtemplate>
<asp:dropdownlist Width="90px" ID="Members"
CssClass="Standard-text" DataSource='<%# BindMembers
(_timeEdit.Department, _timeEdit.Members) %>'
DataTextField="Members" DataValueField="Members"
Runat="server" >
</asp:dropdownlist>
</edititemtemplate>

Thanks
Arthur