<tr>
                <td >
                    Escolha um perfil
                </td>
                <td>
                    <asp:DropDownList ID="mostraUsuarios" runat="server" >
                    </asp:DropDownList>
                    <asp:Button runat="server" Text="Carregar perfil" OnClick="carregaPerfilUsuario"/>
                </td>
            </tr>






protected void carregaPerfilUsuario(object sender, EventArgs e)
        {

            String nome = mostraUsuarios.SelectedItem.Value;    // pega valor do dropDownList

            SqlConnection conn = new SqlConnection("Data Source=sqlserver01.webint.com.br;Initial Catalog=webint;Persist Security Info=True;User ID=webint;Password=igor1990");
            SqlDataReader reader = null;
            SqlCommand cmm = new SqlCommand("select * from tb_usuarios where nome = '" +nome+"'", conn);
            try
            {
                conn.Open();
                reader = cmm.ExecuteReader();
                editar_nome.Text = reader.GetString(2);
                editar_email.Text = reader.GetString(3);
                editar_telefone.Text = reader.GetString(5);
            }
            catch (Exception ex)
            {
                // throw ex;
            }
            finally
            {
                conn.Close();
                conn.Dispose();
            }

        }