Permissions per content items are not available out of the box in 3.x editions. We will have granular permissions in Sitefinity 4.0 which CTP is available for downloading.
You can implement granular permissions in 3.x edition by creating a web service that will be used to bind RadGrid control used in GenericContent based modules. Inside your webservice you can check the current user and apply some additional restrictions over it.
Just to let you know that this thread is used for questions related to Sitefinity 4.0. Please use appropriate thread for 3.x edition.
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