Hi Nicole
How I would implement this would to be create a Link Reason of Subscriber and then associate the users against the item using this link reason.
When a new change is logged use a combination of the Action processor to recognise the new change being logged and then call SmartMail to grab, via a data generation activity, the list of users subscribed to the item used in the change.
You then use that array to send the emails via an email activity.
You could take this even further by adding a service offering in your service catalogue to allow users to subscribe and unsubscribe from items which can be fully automated via the ETM.
If you are unsure about how to implement the above contact your account manager or local assyst consultant who would be happy to discuss this further with you.
Regards
Steve