Import namespace directive & imports directive

What is the difference between the directives  <%@ Import Namespace="System.Data.SQLClient" %> in design page and the Imports System.Data.SqlClient in the code behind page???
I supposed to be the same but if I imported the namespace in design page I were not able to use the class SQLConnection in the code behind page until I set IMPORTS in this page too.
To construct connection object I were forced to use

conn ...