Identify a Repeater Item Text value when paging through a GridView

I have  GridView that I use to show a grid of book titles and related information.  I have a Repeater Control on the same page that displays an alphabet list of LinkButtons that is used to control the group of books shown.  In short when I select the "B" link button all I see is a grid of books that have titles starting with "B."

My problem comes when the number of books in an alphabetic group exceeds my GridView property PageSize="15".  When paging beyond the first page I apparently need to reacquire the Text value of the already selected LinkButton in the Repeater control so that I can place it in the database Select statement.   How does the GridView1_PageIndexChanging know what LinkButton.Text value to put into 'myAlpha' in the Select statement?

       <asp:Repeater ID="FilteringUI" runat="server"  
               onitemcommand="FilteringUI_ItemCommand" >
            <ItemTemplate>
                <asp:LinkButton runat="server"  ID="lnkFilter"  
                                Text='<%# Container.DataItem %>'
                                CommandName='<%# Container.DataItem %>' >
                      </asp:LinkButton>
            </ItemTemplate>
         </asp:Repeater>

    <asp:GridView ID="GridView1" runat="server"  
        AutoGenerateColumns="False" AllowPaging="True"  PageSize="15"
            PagerSettings-PageButtonCount="25"
             OnPageIndexChanging="GridView1_PageIndexChanging"
            PagerSettings-Mode="NumericFirstLast"  
             PagerSettings-Position="TopAndBottom"  
             >
        <Columns>
            <asp:BoundField  HeaderText="title" DataField="titlelink" />
            <asp:BoundField DataField="imagelink" />
            <asp:BoundField HeaderText="Description" DataField="desc" />
        </Columns>
    </asp:GridView>
   
   private void BindFilteringUI()
    {
        string[] filterOptions = { "1-9", "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P",  "Q", "R", "S", "T", "U", "V", "W", "Y" };
        FilteringUI.DataSource = filterOptions;
        FilteringUI.DataBind();
    }

    protected void Grid_Fill()
    {
        string selectSQL;

        selectSQL = "select title, titlelink + author as titlelink, imagelink, [desc] ";
        selectSQL += " from tblbooks ";
        selectSQL += " where left(title, 1) " + myAlpha + " order by title ";

        DataTable dt = new DataTable();
        SqlConnection con = new SqlConnection(connectionString);

        try
        {
            con.Open();
            SqlCommand cmd = new SqlCommand(selectSQL, con);
            SqlDataAdapter sqlDa = new SqlDataAdapter(cmd);
            sqlDa.Fill(dt);

            if (dt.Rows.Count > 0)
            {
                GridView1.DataSource = dt;
                GridView1.DataBind();
            }
        }
        catch (System.Data.SqlClient.SqlException ex)
        {
            string msg = "Fetch Error:";
            msg += ex.Message;
            throw new Exception(msg);
        }
        finally
        {
            con.Close();
        }
    }

    protected void FilteringUI_ItemCommand(object source, RepeaterCommandEventArgs e)
    {
        switch (e.CommandName)
        {
            case "1-9":
                myAlpha = " in ('0','1','2','3','4','5','6','7','8','9') ";
                break;
            case "A":
                myAlpha = " ='A' ";
                break;
            case "B":
                myAlpha = " ='B' ";
                break;
            case "C":
                myAlpha = " ='C' ";
                break;
          // etc. . . .
          }

}

    protected void GridView1_PageIndexChanging(object sender, EventArgs e)
    {
       //essentially the same as Grid_Fill()

            string selectSQL;
                selectSQL = "select title, titlelink + author as titlelink, imagelink, [desc] ";
                selectSQL += " from tblbooks ";
                selectSQL += " where left(title, 1) " + myAlpha + " order by title ";

            DataTable dt = new DataTable();
            SqlConnection con = new SqlConnection(connectionString);

            try
            {
                con.Open();
                SqlCommand cmd = new SqlCommand(selectSQL, con);
                SqlDataAdapter sqlDa = new SqlDataAdapter(cmd);
                sqlDa.Fill(dt);

                if (dt.Rows.Count > 0)
                {
                    GridView1.DataSource = dt;
                    GridView1.DataBind();
                }
            }
            catch (System.Data.SqlClient.SqlException ex)
            {
                string msg = "Fetch Error:";
                msg += ex.Message;
                throw new Exception(msg);
            }
            finally
            {
                con.Close();
            }
    }