How setup macports package bash to be used from terminal.app
From man chsh
The shell field is the command interpreter the user prefers.  If the shell field
is empty, the Bourne shell, /bin/sh, is assumed.  When altering a login shell, and
not the super-user, the user may not change from a non-standard shell or to a
non-standard shell.  Non-standard is defined as a shell not found in /etc/shells.

So to change your shell to /opt/local/bin/bash run
grep -q '^/opt/local/bin/bash' /etc/shells || sudo sh -c 'echo /opt/local/bin/bash &gt;&gt; /etc/shells'
chsh -s /opt/local/bin/bash

If you use bash as your login shell (which is what chsh and the default for Terminal.app do) then if you don't have ~/.bash_profile then bash will automatically read ~/.profile (but as you are using bash you should be using ~/.bash_profile)
Terminal.app by default runs login which runs the shell set by chsh and that should be loading macports bash and then ~/.profile