add history point to gridview results for browser back button

I have a Combobox and GridView on the Content page. I do bind the GridView on Combobox SelectedIndex Changed event using AJAX. I would like to create an HistoryPoint for this Combobox selected value and GridView results when the back button is clicked. I am not sure how to get this functionality done. I have seen GridView with Paging in the forums. Could you please suggest?  I have this code so far.
<asp:ScriptManagerProxy ID="ProxyScriptManager" runat="server" OnNavigate="OnNavigateHistory" />
 private static String key = "s";
 protected void ComboBox1_SelectedIndexChanged(object o, Web.UI.ComboBoxSelectedIndexChangedEventArgs e)  {
          GridView.DataSource = myDataTable           GridView1.DataBind();           ScriptManager.GetCurre ...