Is the portal like an open door through which you can see the remote location, and things can pass freely either way? Then I would say yes.
Is the portal a swirling opaque mist through which you can step and be transported to the other side? It would make sense that you could project physical things through, including for example a fire bolt, but you wouldn't have any ability to target a spell, so anything requiring seeing the target would be out of the question.
Is the portal a magical field which transports you when you touch it? Probably you could not extend magic through it in that case. You're either on one side or the other but there's no possibility to reach physically or magically through it.
